rfc9499xml2.original.xml   rfc9499.xml 
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<?rfc toc="yes"?> <rfc xmlns:xi="http://www.w3.org/2001/XInclude" docName="draft-ietf-dnsop-rfc849
<?rfc tocdepth="4"?> 9bis-10" number="9499" ipr="trust200902" submissionType="IETF" category="bcp" co
<?rfc sortrefs="yes"?> nsensus="true" obsoletes="8499" updates="2308" xml:lang="en" tocInclude="true" t
<?rfc symrefs="yes"?> ocDepth="4" sortRefs="false" symRefs="true" version="3">
<?rfc compact="yes"?>
<?rfc subcompact="no"?>
<rfc docName="draft-ietf-dnsop-rfc8499bis-10"
ipr="trust200902" category="bcp" obsoletes="8499" updates="2308" consensu
s="yes">
<front>
<title abbrev="DNS Terminology">DNS Terminology</title>
<author initials="P." surname="Hoffman" fullname="Paul Hoffman">
<organization>ICANN</organization>
<address>
<email>paul.hoffman@icann.org</email>
</address>
</author>
<author initials="K." surname="Fujiwara" fullname="Kazunori Fujiwara">
<organization abbrev="JPRS">Japan Registry Services Co., Ltd.</organization>
<address>
<email>fujiwara@jprs.co.jp</email>
</address>
</author>
<date/>
<area>Internet</area>
<keyword>vocabulary, domain name system</keyword>
<abstract>
<t>The Domain Name System (DNS) is defined in literally dozens of <front>
<title abbrev="DNS Terminology">DNS Terminology</title>
<seriesInfo name="RFC" value="9499"/>
<seriesInfo name="BCP" value="219"/>
<author initials="P." surname="Hoffman" fullname="Paul Hoffman">
<organization>ICANN</organization>
<address>
<email>paul.hoffman@icann.org</email>
</address>
</author>
<author initials="K." surname="Fujiwara" fullname="Kazunori Fujiwara">
<organization abbrev="JPRS">Japan Registry Services Co., Ltd.</organizatio
n>
<address>
<email>fujiwara@jprs.co.jp</email>
</address>
</author>
<date year="2024" month="March"/>
<area>ops</area>
<workgroup>dnsop</workgroup>
<keyword>vocabulary</keyword>
<keyword>domain name system</keyword>
<abstract>
<t>The Domain Name System (DNS) is defined in literally dozens of
different RFCs. The terminology used by implementers and developers of different RFCs. The terminology used by implementers and developers of
DNS protocols, and by operators of DNS systems, has changed DNS protocols, and by operators of DNS systems, has changed
in the decades since the DNS was first defined. This document gives in the decades since the DNS was first defined. This document gives
current definitions for many of the terms used in the DNS in a single current definitions for many of the terms used in the DNS in a single
document.</t> document.</t>
<t>This document updates RFC 2308 by clarifying the definitions of "forwar
<t>This document updates RFC 2308 by clarifying the definitions of "forwarder" a der" and "QNAME".
nd "QNAME".
It obsoletes RFC 8499 by adding multiple terms and clarifications. It obsoletes RFC 8499 by adding multiple terms and clarifications.
Comprehensive lists of changed and new definitions can be found in Appendices A and B.</t> Comprehensive lists of changed and new definitions can be found in Appendices A and B.</t>
</abstract>
</abstract> </front>
<middle>
</front> <section anchor="introduction" numbered="true" toc="default">
<name>Introduction</name>
<middle> <t>The Domain Name System (DNS) is a simple query-response protocol
whose messages in both directions have the same format. (<xref target="names" f
<section anchor="introduction" title="Introduction"> ormat="default"/> gives a definition of "global DNS", which is often
<t>The Domain Name System (DNS) is a simple query-response protocol
whose messages in both directions have the same format. (<xref
target="names"/> gives a definition of "global DNS", which is often
what people mean when they say "the DNS".) The protocol and message what people mean when they say "the DNS".) The protocol and message
format are defined in <xref target="RFC1034"/> and <xref format are defined in <xref target="RFC1034" format="default"/> and <xref target
target="RFC1035"/>. These RFCs defined some terms, and later documents ="RFC1035" format="default"/>. These RFCs defined some terms, and later document
defined others. Some of the terms from <xref target="RFC1034"/> and s
<xref target="RFC1035"/> have somewhat different meanings now than defined others. Some of the terms from <xref target="RFC1034" format="default"/>
and
<xref target="RFC1035" format="default"/> have somewhat different meanings now t
han
they did in 1987.</t> they did in 1987.</t>
<t>This document contains a collection of a wide variety of DNS-related te
<t>This document contains a collection of a wide variety of DNS-related terms, rms,
organized loosely by topic. Some of them have been precisely defined in earlier organized loosely by topic. Some of them have been precisely defined in earlier
RFCs, some have been loosely defined in earlier RFCs, and some are not defined RFCs, some have been loosely defined in earlier RFCs, and some are not defined
in an earlier RFC at all.</t> in an earlier RFC at all.</t>
<t>Other organizations sometimes define DNS-related terms in their own way
<t>Other organizations sometimes define DNS-related terms their own way. .
For example, the WHATWG defines "domain" at For example, the WHATWG defines "domain" at <eref brackets="angle" target="https
&lt;https://url.spec.whatwg.org/&gt;. ://url.spec.whatwg.org/"/>.
The Root Server System Advisory Committee (RSSAC) has a good The Root Server System Advisory Committee (RSSAC) has a good
lexicon <xref target="RSSAC026"/>. lexicon <xref target="RSSAC026" format="default"/>.
</t> </t>
<t>Most of the definitions listed here represent the consensus definition
<t>Most of the definitions listed here represent the consensus definition of the of the DNS
DNS
community -- both protocol developers and operators. Some of the definitions community -- both protocol developers and operators. Some of the definitions
differ from earlier RFCs, and those differences are noted. differ from earlier RFCs, and those differences are noted.
In this document, where the consensus definition is the same as the one in In this document, where the consensus definition is the same as the one in
an RFC, that RFC is quoted. Where the consensus definition has changed somewhat, an RFC, that RFC is quoted. Where the consensus definition has changed somewhat,
the RFC is mentioned but the new stand-alone definition is given. the RFC is mentioned but the new stand-alone definition is given.
See <xref target="updates-list"/> for a list of the definitions See <xref target="updates-list" format="default"/> for a list of the definitions
that this document updates.</t> that this document updates.</t>
<t>It is important to note that,
<t>It is important to note that,
during the development of this document, it became clear that some DNS-related t erms during the development of this document, it became clear that some DNS-related t erms
are interpreted quite differently by different DNS experts. Further, some terms are interpreted quite differently by different DNS experts. Further, some terms
that are defined in early DNS RFCs now have definitions that are generally agree d to, but that are defined in early DNS RFCs now have definitions that are generally agree d to, but
that are different from the original definitions. that are different from the original definitions.
This document is a small revision to <xref target="RFC8499"/>; that document was This document is a small revision to <xref target="RFC8499" format="default"/>;
a substantial revision to <xref target="RFC7719"/>.</t> that document was
a substantial revision to <xref target="RFC7719" format="default"/>.</t>
<t>Note that there is no single consistent definition of "the DNS". It can be co <t>Note that there is no single consistent definition of "the DNS". It can
nsidered to be some be considered to be some
combination of the following: a commonly used naming scheme for objects on the I nternet; a distributed database representing combination of the following: a commonly used naming scheme for objects on the I nternet; a distributed database representing
the names and certain properties of these objects; an architecture providing dis tributed the names and certain properties of these objects; an architecture providing dis tributed
maintenance, resilience, and loose coherency for this database; and a simple que ry-response protocol maintenance, resilience, and loose coherency for this database; and a simple que ry-response protocol
(as mentioned below) implementing this architecture. <xref target="names"/> defi nes (as mentioned below) implementing this architecture. <xref target="names" format ="default"/> defines
"global DNS" and "private DNS" as a way to deal with these differing definitions .</t> "global DNS" and "private DNS" as a way to deal with these differing definitions .</t>
<t>Capitalization in DNS terms is often inconsistent among RFCs and
<t>Capitalization in DNS terms is often inconsistent among RFCs and
various DNS practitioners. The capitalization used in this document is a best various DNS practitioners. The capitalization used in this document is a best
guess at current practices, and is not meant to indicate that other guess at current practices, and is not meant to indicate that other
capitalization styles are wrong or archaic. capitalization styles are wrong or archaic.
In some cases, multiple styles of capitalization are used for the same term due to quoting In some cases, multiple styles of capitalization are used for the same term due to quoting
from different RFCs.</t> from different RFCs.</t>
<t>In this document, the words "byte" and "octet" are used interchangeably
<t>In this document, the words "byte" and "octet" are used interchangably. .
They both appear here because they both appear in the earlier RFCs that defined They appear here because they both appear in the earlier RFCs that defined terms
terms in the DNS.</t> in the DNS.</t>
<t>Readers should note that the terms in this document are grouped by topi
<t>Readers should note that the terms in this document are grouped by topic. c.
Someone who is not already familiar with the DNS probably cannot Someone who is not already familiar with the DNS probably cannot
learn about the DNS from scratch by reading this document from front to back. learn about the DNS from scratch by reading this document from front to back.
Instead, skipping around may be the only way to get enough context to Instead, skipping around may be the only way to get enough context to
understand some of the definitions. This document has an index that might be use ful for understand some of the definitions. This document has an index that might be use ful for
readers who are attempting to learn the DNS by reading this document.</t> readers who are attempting to learn the DNS by reading this document.</t>
</section>
</section> <section anchor="names" numbered="true" toc="default">
<name>Names</name>
<section anchor="names" title="Names"> <dl newline="false" spacing="normal">
<t><list style="hanging"> <dt>Naming system:</dt>
<dd>
<t hangText='Naming system:'> <t><iref item="Naming system" subitem="" primary="false"/>
<iref item='Naming system'/>
A naming system associates names with data. Naming systems have many significant facets A naming system associates names with data. Naming systems have many significant facets
that help differentiate them from each other. Some commonly identified facets in clude: that help differentiate them from each other. Some commonly identified facets in clude:
<list style="symbols"> </t>
<t>Composition of names</t> <ul spacing="normal">
<t>Format of names</t> <li>Composition of names</li>
<t>Administration of names</t> <li>Format of names</li>
<t>Types of data that can be associated with names</t> <li>Administration of names</li>
<t>Types of metadata for names</t> <li>Types of data that can be associated with names</li>
<t>Protocol for getting data from a name</t> <li>Types of metadata for names</li>
<t>Context for resolving a name</t> <li>Protocol for getting data from a name</li>
</list></t> <li>Context for resolving a name</li>
</ul>
<t>Note that this list is a small subset of facets that people have identified o </dd>
ver time <dt/>
<dd>Note that this list is a small subset of facets that people have ide
ntified over time
for naming systems, and the IETF has yet to agree on a good set of facets that c an be used for naming systems, and the IETF has yet to agree on a good set of facets that c an be used
to compare naming systems. For example, other facets might include "protocol to update to compare naming systems. For example, other facets might include "protocol to update
data in a name", "privacy of names", and "privacy of data associated with names" , but data in a name", "privacy of names", and "privacy of data associated with names" , but
those are not as well defined as the ones listed above. The list here is chosen because it those are not as well defined as the ones listed above. The list here is chosen because it
helps describe the DNS and naming systems similar to the DNS.</t> helps describe the DNS and naming systems similar to the DNS.</dd>
<dt>Domain name:</dt>
<t hangText='Domain name:'> <dd>
<iref item='Domain name'/> <iref item="Domain name" subitem="" primary="false"/>
An ordered list of one or more labels.</t> An ordered list of one or more labels.</dd>
<dt/>
<t>Note that this is a definition independent of the DNS RFCs (<xref target="RFC <dd>Note that this is a definition independent of the DNS RFCs (<xref ta
1034"/> and <xref target="RFC1035"/>), and the definition here rget="RFC1034" format="default"/> and <xref target="RFC1035" format="default"/>)
also applies to systems other than the DNS. <xref target="RFC1034"/> defines the , and the definition here
"domain also applies to systems other than the DNS. <xref target="RFC1034" format="defau
lt"/> defines the "domain
name space" using mathematical trees and their nodes in graph theory, and that d efinition name space" using mathematical trees and their nodes in graph theory, and that d efinition
has the same practical result as the definition here. Any path of a directed acy clic graph has the same practical result as the definition here. Any path of a directed acy clic graph
can be represented by a domain name consisting of the labels of its nodes, order ed by can be represented by a domain name consisting of the labels of its nodes, order ed by
decreasing distance from the root(s) (which is the normal convention within the DNS, decreasing distance from the root(s) (which is the normal convention within the DNS,
including this document). A domain name whose last label identifies a root of th e graph is including this document). A domain name whose last label identifies a root of th e graph is
fully qualified; other domain names whose labels form a strict prefix of a fully fully qualified; other domain names whose labels form a strict prefix of a fully
-qualified qualified
domain name are relative to its first omitted node.</t> domain name are relative to its first omitted node.</dd>
<dt/>
<t>Also note that different IETF and non-IETF documents have used the term "doma <dd>Also note that different IETF and non-IETF documents have used the t
in name" erm "domain name"
in many different ways. It is common for earlier documents to use "domain name" to mean in many different ways. It is common for earlier documents to use "domain name" to mean
"names that match the syntax in <xref target="RFC1035"/>", but possibly with add itional "names that match the syntax in <xref target="RFC1035" format="default"/>", but possibly with additional
rules such as "and are, or will be, resolvable in the global DNS" or "but only u sing the rules such as "and are, or will be, resolvable in the global DNS" or "but only u sing the
presentation format".</t> presentation format".</dd>
<dt>Label:</dt>
<t hangText='Label:'> <dd>
<iref item='Label'/> <iref item="Label" subitem="" primary="false"/>
An ordered list of zero or more octets that makes up a portion of a domain name. An ordered list of zero or more octets that makes up a portion of a domain name.
Using graph theory, a label identifies one node in a portion of the graph of all possible Using graph theory, a label identifies one node in a portion of the graph of all possible
domain names.</t> domain names.</dd>
<dt>Global DNS:</dt>
<t hangText='Global DNS:'> <dd>
<iref item='Global DNS'/> <iref item="Global DNS" subitem="" primary="false"/>
Using the short set of facets listed in "Naming system", the global DNS can be d efined as Using the short set of facets listed in "Naming system", the global DNS can be d efined as
follows. Most of the rules here come from <xref target="RFC1034"/> and <xref follows. Most of the rules here come from <xref target="RFC1034" format="default
target="RFC1035"/>, although the term "global DNS" has not been defined before n "/> and <xref target="RFC1035" format="default"/>, although the term "global DNS
ow.</t> " has not been defined before now.</dd>
<dt/><dd>
<t>Composition of names: A name in the global DNS has one or more <dl newline="false">
<dt>
Composition of names:</dt><dd>A name in the global DNS has one or more
labels. The length of each label is between 0 and 63 octets labels. The length of each label is between 0 and 63 octets
inclusive. In a fully-qualified domain name, the last label inclusive. In a fully qualified domain name, the last label
in the ordered list is 0 octets long; it is the only label whose in the ordered list is 0 octets long; it is the only label whose
length may be 0 octets, and it is called the "root" or "root label". length may be 0 octets, and it is called the "root" or "root label".
A domain name in the global DNS has a maximum total length of 255 A domain name in the global DNS has a maximum total length of 255
octets in the wire format; the root represents one octet for this octets in the wire format; the root represents one octet for this
calculation. calculation.
(Multicast DNS <xref target="RFC6762"/> allows names up to 255 bytes plus a term inating zero byte (Multicast DNS <xref target="RFC6762" format="default"/> allows names up to 255 bytes plus a terminating zero byte
based on a different interpretation of RFC 1035 and what is included in the 255 octets.) based on a different interpretation of RFC 1035 and what is included in the 255 octets.)
</t> </dd>
<dt>Format of names:</dt><dd>Names in the global DNS are domain names.
<t>Format of names: Names in the global DNS are domain names. There are three fo There are three formats:
rmats: wire format, presentation format, and common display.</dd><dt/><dd>
wire format, presentation format, and common display. <dl spacing="normal">
<list style="empty"> <dt>Wire format:</dt><dd>The basic wire format for names in the
<t>The basic wire format for names in the global DNS is a list of labels ordered global DNS is a list of labels ordered by decreasing distance from
by the root, with the root label last. Each label is preceded by a
decreasing distance from the root, with the root label last. Each label is prece length octet. <xref target="RFC1035" format="default"/> also
ded by a defines a compression scheme that modifies this format.</dd>
length octet. <xref target="RFC1035"/> also defines a compression scheme that mo <dt>Presentation format:</dt><dd>The presentation format for names
difies in the global DNS is a list of labels ordered by decreasing
this format.</t> distance from the root, encoded as ASCII, with a "." character
between each label. In presentation format, a fully qualified
<t>The presentation format for names in the global DNS is a list of labels order domain name includes the root label and the associated separator
ed by dot. For example, in presentation format, a fully qualified domain
decreasing distance from the root, encoded as ASCII, with a "." character betwee name with two non-root labels is always shown as "example.tld."
n each instead of "example.tld". <xref target="RFC1035"
label. In presentation format, a fully-qualified domain name includes the root l format="default"/> defines a method for showing octets that do not
abel and display in ASCII.</dd>
the associated separator dot. For example, in presentation format, a fully-quali <dt>Common display format:</dt><dd>The common display format is
fied used in applications and free text. It is the same as the
domain name with two non-root labels is always shown as "example.tld." instead o presentation format, but showing the root label and the "." before
f it is optional and is rarely done. For example, in common display
"example.tld". <xref target="RFC1035"/> defines a method for showing octets that format, a fully qualified domain name with two non-root labels is
do not usually shown as "example.tld" instead of "example.tld.". Names in
display in ASCII.</t> the common display format are normally written such that the
directionality of the writing system presents labels by decreasing
<t>The common display format is used in applications and free text. It is the sa distance from the root (so, in both English and the C programming
me as the language, the root or Top-Level Domain (TLD) label in the ordered
presentation format, but showing the root label and the "." before it is optiona list is rightmost; but in Arabic, it may be leftmost, depending on
l and is local conventions).</dd>
rarely done. For example, in common display format, a fully-qualified domain nam </dl>
e with two </dd>
non-root labels is usually shown as "example.tld" instead of "example.tld.". Nam <dt>Administration of names:</dt><dd>Administration is specified by dele
es in the gation (see the
common display format are normally written such that the directionality of the w definition of "delegation" in <xref target="zones" format="default"/>). Policie
riting s for administration of
system presents labels by decreasing distance from the root (so, in both English
and the C programming language the
root or Top-Level Domain (TLD) label in the ordered list is rightmost; but in Ar
abic, it may be leftmost,
depending on local conventions).</t></list></t>
<t>Administration of names: Administration is specified by delegation (see the
definition of "delegation" in <xref target="zones"/>). Policies for administrat
ion of
the root zone in the global DNS are determined by the names operational communit y, which the root zone in the global DNS are determined by the names operational communit y, which
convenes itself in the Internet Corporation for Assigned Names and Numbers (ICAN N). The convenes itself in the Internet Corporation for Assigned Names and Numbers (ICAN N). The
names operational community selects the IANA Functions Operator for the global D NS root names operational community selects the IANA Functions Operator for the global D NS root
zone. zone.
The name servers that serve the root zone are provided by independent The name servers that serve the root zone are provided by independent
root operators. Other zones in the global DNS have their own policies for root operators. Other zones in the global DNS have their own policies for
administration.</t> administration.</dd>
<dt>Types of data that can be associated with names:</dt><dd>A name can
<t>Types of data that can be associated with names: A name can have zero or more have zero or more
resource records associated with it. There are numerous types of resource record s with resource records associated with it. There are numerous types of resource record s with
unique data structures defined in many different RFCs and in the IANA registry a unique data structures defined in many different RFCs and in the IANA registry a
t <xref t <xref target="IANA_Resource_Registry" format="default"/>.</dd>
target="IANA_Resource_Registry"/>.</t> <dt>Types of metadata for names:</dt><dd>Any name that is published in t
he DNS appears as a set
<t>Types of metadata for names: Any name that is published in the DNS appears as of resource records (see the definition of "RRset" in <xref target="rrs" format=
a set "default"/>). Some names
of resource records (see the definition of "RRset" in <xref target="rrs"/>). So
me names
do not, themselves, have data associated with them in the DNS, but they "appear" in the DNS do not, themselves, have data associated with them in the DNS, but they "appear" in the DNS
anyway because they form part of a longer name that does have data associated wi th it (see anyway because they form part of a longer name that does have data associated wi th it (see
the definition of "empty non-terminals" in <xref target="zones"/>).</t> the definition of "empty non-terminals" in <xref target="zones" format="default"
/>).</dd>
<t>Protocol for getting data from a name: The protocol described in <xref <dt>Protocol for getting data from a name:</dt><dd>The protocol describe
target="RFC1035"/>.</t> d in <xref target="RFC1035" format="default"/>.</dd>
<dt>Context for resolving a name:</dt><dd>The global DNS root zone distr
<t>Context for resolving a name: The global DNS root zone distributed by Public ibuted by Public Technical Identifiers (PTI).</dd>
Technical Identifiers (PTI).</t> </dl></dd>
<dt>Private DNS:</dt>
<t hangText='Private DNS:'> <dd>
<iref item='Private DNS'/> <iref item="Private DNS" subitem="" primary="false"/>
Names that use the protocol described in <xref target="RFC1035"/> but that do no Names that use the protocol described in <xref target="RFC1035" format="default"
t rely on /> but do not rely on
the global DNS root zone or names that are otherwise not generally available on the the global DNS root zone or names that are otherwise not generally available on the
Internet but are using the protocol described in <xref target="RFC1035"/>. A sy stem can Internet but are using the protocol described in <xref target="RFC1035" format=" default"/>. A system can
use both the global DNS and one or more private DNS systems; for example, see "S plit DNS" use both the global DNS and one or more private DNS systems; for example, see "S plit DNS"
in <xref target="dns-servers-and-clients"/>.</t> in <xref target="dns-servers-and-clients" format="default"/>.</dd>
<dt/>
<t>Note that domain names that do not appear in the DNS, and that are intended n <dd>Note that domain names that do not appear in the DNS and that are in
ever to be tended never to be
looked up using the DNS protocol, are not part of the global DNS or a private DN looked up using the DNS protocol are not part of the global DNS or a private DNS
S even , even
though they are domain names.</t> though they are domain names.</dd>
<dt>Multicast DNS (mDNS):</dt>
<t hangText='Multicast DNS (mDNS):'> <dd>
<iref item='Multicast DNS'/> <iref item="Multicast DNS" subitem="" primary="false"/>
<iref item='mDNS'/> <iref item="mDNS" subitem="" primary="false"/>
<!--Begin DNE text -->
"Multicast DNS (mDNS) provides the ability to perform DNS-like operations on the local link in the "Multicast DNS (mDNS) provides the ability to perform DNS-like operations on the local link in the
absence of any conventional Unicast DNS server. In addition, Multicast DNS desi gnates a portion of absence of any conventional Unicast DNS server. In addition, Multicast DNS desi gnates a portion of
the DNS namespace to be free for local use, without the need to pay any annual f ee, and without the the DNS namespace to be free for local use, without the need to pay any annual f ee, and without the
need to set up delegations or otherwise configure a conventional DNS server to a nswer for those need to set up delegations or otherwise configure a conventional DNS server to a nswer for those
names." (Quoted from <xref target="RFC6762"/>, Abstract) names." (Quoted from <xref target="RFC6762" format="default"/>, Abstract)
<!--End DNE text -->
Although it uses a compatible wire format, mDNS is, strictly speaking, a differe nt protocol than DNS. Although it uses a compatible wire format, mDNS is, strictly speaking, a differe nt protocol than DNS.
Also, where the above quote says "a portion of the DNS namespace", it would be c learer to say "a Also, where the above quote says "a portion of the DNS namespace", it would be c learer to say "a
portion of the domain name space". The names in mDNS are not intended to be loo ked up in the portion of the domain name space". The names in mDNS are not intended to be loo ked up in the
DNS.</t> DNS.</dd>
<dt>Locally served DNS zone:</dt>
<t hangText='Locally served DNS zone:'> <dd>
<iref item='Locally served DNS zone'/> <iref item="Locally served DNS zone" subitem="" primary="false"/>
A locally served DNS zone is a special case of private DNS. A locally served DNS zone is a special case of private DNS.
Names are resolved using the DNS protocol in a local context. Names are resolved using the DNS protocol in a local context.
<xref target="RFC6303"/> defines subdomains of IN-ADDR.ARPA <xref target="RFC6303" format="default"/> defines subdomains of IN-ADDR.ARPA
that are locally served zones. that are locally served zones.
Resolution of names through locally served zones may result in ambiguous results . Resolution of names through locally served zones may result in ambiguous results .
For example, the same name may resolve to different results in different locally served DNS For example, the same name may resolve to different results in different locally served DNS
zone contexts. The context for a locally served DNS zone may be explicit, such as those that are listed in zone contexts. The context for a locally served DNS zone may be explicit, such as those that are listed in
<xref target="RFC6303"/> and <xref target="RFC7793"/>, or implicit, such as thos <xref target="RFC6303" format="default"/> and <xref target="RFC7793" format="def
e defined by local DNS administration and not known to the ault"/>, or implicit, such as those defined by local DNS administration and not
resolution client.</t> known to the
resolution client.</dd>
<t hangText='Fully-Qualified Domain Name (FQDN):'> <dt>Fully Qualified Domain Name (FQDN):</dt>
<iref item='Fully-qualified domain name (FQDN)'/> <dd>
<iref item="Fully Qualified Domain Name (FQDN)" subitem="" primary="fa
lse"/>
This is often just a clear way This is often just a clear way
of saying the same thing as "domain name of a node", as outlined of saying the same thing as "domain name of a node", as outlined
above. However, the term is ambiguous. Strictly speaking, a fully-qualified above. However, the term is ambiguous. Strictly speaking, a fully qualified
domain name would include every label, including the zero-length label domain name would include every label, including the zero-length label
of the root: such a name would be written "www.example.net." of the root; such a name would be written "www.example.net."
(note the terminating dot). But, because every name eventually shares (note the terminating dot). But, because every name eventually shares
the common root, names are often written relative to the root the common root, names are often written relative to the root
(such as "www.example.net") and are still called "fully qualified". (such as "www.example.net") and are still called "fully qualified".
This term first appeared in <xref target="RFC0819"/>. In this document, names This term first appeared in <xref target="RFC0819" format="default"/>. In this d
are often written relative to the root.</t> ocument, names
<t>The need for the term "fully-qualified domain name" comes from the existence are often written relative to the root.</dd>
<dt/>
<dd>The need for the term "fully qualified domain name" comes from the e
xistence
of partially qualified domain names, which are names where one or more of partially qualified domain names, which are names where one or more
of the last labels in the ordered list are omitted (for example, of the last labels in the ordered list are omitted (for example,
a domain name of "www" relative to "example.net" identifies "www.example.net"). a domain name of "www" relative to "example.net" identifies "www.example.net").
Such relative names are understood only by context.</t> Such relative names are understood only by context.</dd>
<dt>Host name:</dt>
<t hangText='Host name:'> <dd>
<iref item='Host name'/> <iref item="Host name" subitem="" primary="false"/>
This term and its equivalent, "hostname", have been This term and its equivalent, "hostname", have been
widely used but are not defined in <xref target="RFC1034"/>, <xref target="RFC10 widely used but are not defined in <xref target="RFC1034" format="default"/>, <x
35"/>, ref target="RFC1035" format="default"/>,
<xref target="RFC1123"/>, or <xref target="RFC2181"/>. The <xref target="RFC1123" format="default"/>, or <xref target="RFC2181" format="def
ault"/>. The
DNS was originally deployed into the Host Tables environment as DNS was originally deployed into the Host Tables environment as
outlined in <xref target="RFC0952"/>, and it is likely that the term followed outlined in <xref target="RFC0952" format="default"/>, and it is likely that the term followed
informally from the definition there. informally from the definition there.
Over time, the definition seems Over time, the definition seems
to have shifted. "Host name" is often meant to be a domain name that follows to have shifted. "Host name" is often meant to be a domain name that follows
the rules in Section 3.5 of <xref target="RFC1034"/>, which is also called the " preferred name the rules in <xref target="RFC1034" sectionFormat="of" section="3.5"/>, which is also called the "preferred name
syntax". (In that syntax, every character in each label is a letter, syntax". (In that syntax, every character in each label is a letter,
a digit, or a hyphen). Note that any label in a domain name can contain any octe t a digit, or a hyphen). Note that any label in a domain name can contain any octe t
value; hostnames are generally considered to be domain names where value; hostnames are generally considered to be domain names where
every label follows the rules in the "preferred name syntax", with the every label follows the rules in the "preferred name syntax", with the
amendment that labels can start with ASCII digits (this amendment amendment that labels can start with ASCII digits (this amendment
comes from Section 2.1 of <xref target="RFC1123"/>). comes from <xref target="RFC1123" sectionFormat="of" section="2.1"/>).
</t> </dd>
<t>People also sometimes use the term "hostname" to refer to just the first <dt/>
<dd>People also sometimes use the term "hostname" to refer to just the f
irst
label of an FQDN, such as "printer" in "printer.admin.example.com". label of an FQDN, such as "printer" in "printer.admin.example.com".
(Sometimes this is formalized in configuration in operating systems.) (Sometimes this is formalized in configuration in operating systems.)
In addition, people sometimes use this term to In addition, people sometimes use this term to
describe any name that refers to a machine, and those might include describe any name that refers to a machine, and those might include
labels that do not conform to the "preferred name syntax".</t> labels that do not conform to the "preferred name syntax".</dd>
<dt>Top-Level Domain (TLD):</dt>
<t hangText='Top-Level Domain (TLD):'> <dd>
<iref item='TLD'/> <iref item="TLD" subitem="" primary="false"/>
A Top-Level Domain is a zone that is one layer below the A Top-Level Domain is a zone that is one layer below the
root, such as "com" or "jp". There is nothing special, from the point root, such as "com" or "jp". There is nothing special, from the point
of view of the DNS, about TLDs. Most of them are also of view of the DNS, about TLDs. Most of them are also
delegation-centric zones (defined in <xref target="zones"/>), and there are sign ificant policy issues delegation-centric zones (defined in <xref target="zones" format="default"/>), a nd there are significant policy issues
around their operation. around their operation.
TLDs are often divided into sub-groups such as Country Code Top-Level Domains TLDs are often divided into sub-groups such as Country Code Top-Level Domains
(ccTLDs), Generic Top-Level Domains (gTLDs), and others; the (ccTLDs), Generic Top-Level Domains (gTLDs), and others; the
division is a matter of policy and beyond the scope of this document.</t> division is a matter of policy and beyond the scope of this document.</dd>
<dt>Internationalized Domain Name (IDN):</dt>
<t hangText='Internationalized Domain Name (IDN):'> <dd>
<iref item='Internationalized Domain Name'/> <iref item="Internationalized Domain Name" subitem="" primary="false"/
<iref item='IDN'/> >
<iref item="IDN" subitem="" primary="false"/>
The Internationalized Domain Names for Applications (IDNA) protocol is The Internationalized Domain Names for Applications (IDNA) protocol is
the standard mechanism for handling domain names with non-ASCII the standard mechanism for handling domain names with non-ASCII
characters in applications in the DNS. The current standard at the characters in applications in the DNS. The current standard at the
time of this writing, normally called "IDNA2008", is defined in <xref time of this writing, normally called "IDNA2008", is defined in <xref target="RF
target="RFC5890"/>, <xref target="RFC5891"/>, <xref C5890" format="default"/>, <xref target="RFC5891" format="default"/>, <xref targ
target="RFC5892"/>, <xref target="RFC5893"/>, and <xref et="RFC5892" format="default"/>, <xref target="RFC5893" format="default"/>, and
target="RFC5894"/>. These documents define many IDN-specific terms <xref target="RFC5894" format="default"/>. These documents define many IDN-spec
such as "LDH label", "A-label", and "U-label". <xref ific terms
target="RFC6365"/> defines more terms that relate to such as "LDH label", "A-label", and "U-label". <xref target="RFC6365" format="d
internationalization (some of which relate to IDNs); <xref efault"/> defines more terms that relate to
target="RFC6055"/> has a much more extensive discussion of IDNs, internationalization (some of which relate to IDNs); <xref target="RFC6055" form
including some new terminology.</t> at="default"/> has a much more extensive discussion of IDNs,
including some new terminology.</dd>
<t hangText='Subdomain:'> <dt>Subdomain:</dt>
<iref item='Subdomain'/> <dd>
<iref item="Subdomain" subitem="" primary="false"/>
<!--Begin DNE text -->
"A domain is a subdomain of another domain if it is contained within that domain . This relationship can be tested by "A domain is a subdomain of another domain if it is contained within that domain . This relationship can be tested by
seeing if the subdomain's name ends with the containing domain's name." (Quoted seeing if the subdomain's name ends with the containing domain's name." (Quoted
from <xref target="RFC1034"/>, Section 3.1) from <xref target="RFC1034" sectionFormat="comma" section="3.1"/>)
<!--End DNE text -->
For For
example, in the host name "nnn.mmm.example.com", both "mmm.example.com" and "nnn .mmm.example.com" are subdomains of "example.com". example, in the host name "nnn.mmm.example.com", both "mmm.example.com" and "nnn .mmm.example.com" are subdomains of "example.com".
Note that the comparisons here are done on whole labels; that is, Note that the comparisons here are done on whole labels; that is,
"ooo.example.com" is not a subdomain of "oo.example.com".</t> "ooo.example.com" is not a subdomain of "oo.example.com".</dd>
<dt>Alias:</dt>
<t hangText='Alias:'> <dd>
<iref item='Alias'/> <iref item="Alias" subitem="" primary="false"/>
The owner of a CNAME resource record, or a subdomain of the owner of a The owner of a CNAME resource record, or a subdomain of the owner of a
DNAME resource record (DNAME records are defined in <xref target="RFC6672"/>). S DNAME resource record (DNAME records are defined in <xref target="RFC6672" forma
ee also "canonical name".</t> t="default"/>). See also "canonical name".</dd>
<dt>Canonical name:</dt>
<t hangText='Canonical name:'> <dd>
<iref item='Canonical name'/> <iref item="Canonical name" subitem="" primary="false"/>
A CNAME resource record A CNAME resource record
<!--Begin DNE text -->
"identifies its owner name as an "identifies its owner name as an
alias, and specifies the corresponding canonical name in the RDATA alias, and specifies the corresponding canonical name in the RDATA
section of the RR." (Quoted from <xref target="RFC1034"/>, Section 3.6.2) section of the RR." (Quoted from <xref target="RFC1034" sectionFormat="comma" se
<!--END DNE text --> ction="3.6.2"/>)
This usage of the word "canonical" is related to the mathematical This usage of the word "canonical" is related to the mathematical
concept of "canonical form".</t> concept of "canonical form".</dd>
<dt>CNAME:</dt>
<t hangText='CNAME:'> <dd>
<iref item='CNAME'/> <iref item="CNAME" subitem="" primary="false"/>
<!--Begin DNE-->
"It has been traditional to refer to the [owner] of a CNAME record as 'a "It has been traditional to refer to the [owner] of a CNAME record as 'a
CNAME'. This is unfortunate, as 'CNAME' is an abbreviation of CNAME'. This is unfortunate, as 'CNAME' is an abbreviation of
'canonical name', and the [owner] of a CNAME record is most certainly 'canonical name', and the [owner] of a CNAME record is most certainly
not a canonical name." not a canonical name."
<!--End DNE text -->
(Quoted from <xref target="RFC2181"/>, Section 10.1.1. The quoted
text has been changed from "label" to "owner".)</t></list></t>
</section>
<section anchor="dns-response-codes" title="DNS Response Codes">
<t>Some of the response codes (RCODEs) that are defined in <xref target="RFC1035 (Quoted from <xref target="RFC2181" sectionFormat="comma" section="10.1.1"/>. Th
"/> have acquired their own e quoted
text has been changed from "label" to "owner".)</dd>
</dl>
</section>
<section anchor="dns-response-codes" numbered="true" toc="default">
<name>DNS Response Codes</name>
<t>Some of the response codes (RCODEs) that are defined in <xref target="R
FC1035" format="default"/> have acquired their own
shorthand names. All of the RCODEs are listed at shorthand names. All of the RCODEs are listed at
<xref target="IANA_Resource_Registry"/>, although <xref target="IANA_Resource_Registry" format="default"/>, although
that list uses mixed-case capitalization, while most documents use all caps. that list uses mixed-case capitalization, while most documents use all caps.
Some of the common names for values defined in <xref target="RFC1035"/> are desc ribed in this section. Some of the common names for values defined in <xref target="RFC1035" format="de fault"/> are described in this section.
This section also includes an additional RCODE and a general definition. This section also includes an additional RCODE and a general definition.
The official list of all RCODEs is in the IANA registry.</t> The official list of all RCODEs is in the IANA registry.</t>
<dl newline="false" spacing="normal">
<t><list style="hanging"> <dt>NOERROR:</dt>
<dd>
<t hangText='NOERROR:'> <iref item="NOERROR" subitem="" primary="false"/>
<iref item='NOERROR'/> This RCODE appears as "No error condition" in <xref target="RFC1035" sectionFor
This RCODE appears as "No error condition" in Section 4.1.1 of <xref target="RFC mat="of" section="4.1.1"/>.</dd>
1035"/>.</t> <dt>FORMERR:</dt>
<dd>
<t hangText='FORMERR:'> <iref item="FORMERR" subitem="" primary="false"/>
<iref item='FORMERR'/> This RCODE appears as "Format error - The name server was unable to interpret th
This RCODE appears as "Format error - The name server was unable to interpret th e query" in <xref target="RFC1035" sectionFormat="of" section="4.1.1"/>.</dd>
e query" in Section 4.1.1 of <xref target="RFC1035"/>.</t> <dt>SERVFAIL:</dt>
<dd>
<t hangText='SERVFAIL:'> <iref item="SERVFAIL" subitem="" primary="false"/>
<iref item='SERVFAIL'/>
This RCODE appears as "Server failure - The name server was unable to process th is query due to a problem with the name This RCODE appears as "Server failure - The name server was unable to process th is query due to a problem with the name
server" in Section 4.1.1 of <xref target="RFC1035"/>.</t> server" in <xref target="RFC1035" sectionFormat="of" section="4.1.1"/>.</dd>
<dt>NXDOMAIN:</dt>
<t hangText='NXDOMAIN:'> <dd>
<iref item='NXDOMAIN'/> <iref item="NXDOMAIN" subitem="" primary="false"/>
This RCODE appears as "Name Error [...] this code signifies that the domain name This RCODE appears as "Name Error [...] this code signifies that the domain name
referenced in the query does not exist." in Section 4.1.1 of <xref target="RFC10 referenced in the query does not exist." in <xref target="RFC1035" sectionFormat
35"/>. ="of" section="4.1.1"/>.
<xref target="RFC2308"/> established NXDOMAIN as a synonym for Name Error.</t> <xref target="RFC2308"/> established NXDOMAIN as a synonym for Name Error.</dd>
<dt>NOTIMP:</dt>
<t hangText='NOTIMP:'> <dd>
<iref item='NOTIMP'/> <iref item="NOTIMP" subitem="" primary="false"/>
This RCODE appears as "Not Implemented - The name server does not support the re This RCODE appears as "Not Implemented - The name server does not support the re
quested kind of query" in Section 4.1.1 of <xref target="RFC1035"/>.</t> quested kind of query" in <xref target="RFC1035" sectionFormat="of" section="4.1
.1"/>.</dd>
<t hangText='REFUSED:'> <dt>REFUSED:</dt>
<iref item='REFUSED'/> <dd>
<iref item="REFUSED" subitem="" primary="false"/>
This RCODE appears as "Refused - The name server refuses to perform the specifie d operation for policy reasons. For This RCODE appears as "Refused - The name server refuses to perform the specifie d operation for policy reasons. For
example, a name server may not wish to provide the information to the particular requester, or a example, a name server may not wish to provide the information to the particular requester, or a
name server may not wish to perform a particular operation (e.g., zone transfer) for particular name server may not wish to perform a particular operation (e.g., zone transfer) for particular
data." in Section 4.1.1 of <xref target="RFC1035"/>.</t> data." in <xref target="RFC1035" sectionFormat="of" section="4.1.1"/>.</dd>
<dt>NODATA:</dt>
<t hangText='NODATA:'> <dd>
<iref item='NODATA'/> <iref item="NODATA" subitem="" primary="false"/>
"A pseudo RCODE which indicates that the name is valid, for "A pseudo RCODE which indicates that the name is valid, for
the given class, but [there] are no records of the given type. A NODATA the given class, but [there] are no records of the given type. A NODATA
response has to be inferred from the answer." (Quoted from <xref target="RFC2308 "/>, Section 1) response has to be inferred from the answer." (Quoted from <xref target="RFC2308 " sectionFormat="comma" section="1"/>)
"NODATA is indicated by an answer with the RCODE set to NOERROR and no "NODATA is indicated by an answer with the RCODE set to NOERROR and no
relevant answers in the Answer section. The authority section will relevant answers in the Answer section. The Authority section will
contain an SOA record, or there will be no NS records there." (Quoted from <xref contain an SOA record, or there will be no NS records there." (Quoted from <xref
target="RFC2308"/>, Section 2.2) target="RFC2308" sectionFormat="comma" section="2.2"/>)
Note that referrals have a similar format to NODATA replies; <xref target="RFC23 Note that referrals have a similar format to NODATA replies; <xref target="RFC23
08"/> 08" format="default"/>
explains how to distinguish them.</t> explains how to distinguish them.</dd>
<dt/>
<t>The term "NXRRSET" is sometimes used as a synonym for NODATA. However, this i <dd>The term "NXRRSET" is sometimes used as a synonym for NODATA. Howeve
s a mistake, given r, this is a mistake, given
that NXRRSET is a specific error code defined in <xref target="RFC2136"/>.</t> that NXRRSET is a specific error code defined in <xref target="RFC2136" format="
default"/>.</dd>
<t hangText='Negative response:'> <dt>Negative response:</dt>
<iref item='Negative response'/> <dd>
<iref item="Negative response" subitem="" primary="false"/>
A response that indicates that a particular RRset does not exist A response that indicates that a particular RRset does not exist
or whose RCODE indicates that the nameserver cannot answer. or whose RCODE indicates that the nameserver cannot answer.
Sections 2 and 7 of <xref target="RFC2308"/> describe the types of negative resp Sections <xref target="RFC2308" sectionFormat="bare" section="2"/> and <xref tar
onses in detail.</t> get="RFC2308" sectionFormat="bare" section="7"/> of <xref target="RFC2308"/> de
scribe the types of negative responses in detail.</dd>
</list></t> </dl>
</section>
</section> <section anchor="dns-transactions" numbered="true" toc="default">
<name>DNS Transactions</name>
<section anchor="dns-transactions" title="DNS Transactions"> <t>The header of a DNS message is its first 12 octets. Many of the fields
and flags in
<t>The header of a DNS message is its first 12 octets. Many of the fields and fl the diagrams in Sections <xref target="RFC1035" sectionFormat="bare" section="4.
ags in 1.1"/> through <xref target="RFC1035" sectionFormat="bare" section="4.1.3"/> of
the diagrams in Sections 4.1.1 through 4.1.3 of <xref target="RFC1035"/> are ref <xref target="RFC1035"/> are referred to by their names
erred to by their names
in each diagram. in each diagram.
For example, the response codes are called "RCODEs", For example, the response codes are called "RCODEs",
the data for a record is called the "RDATA", and the the data for a record is called the "RDATA", and the
authoritative answer bit is often called "the AA flag" or "the AA bit".</t> authoritative answer bit is often called "the AA flag" or "the AA bit".</t>
<dl newline="false" spacing="normal">
<dt>Class:</dt>
<dd>
<iref item="Class" subitem="" primary="false"/>
A class "identifies a protocol family or instance of a protocol". (Quoted from
<xref target="RFC1034" sectionFormat="comma" section="3.6"/>)
<t><list style="hanging">
<t hangText='Class:'>
<iref item='Class'/>
A class "identifies a protocol family or instance of a protocol". (Quoted from
<xref
target="RFC1034"/>, Section 3.6)
<!--Begin DNE text -->
"The DNS tags all data with a class as well as the type, so that we can allow pa rallel use "The DNS tags all data with a class as well as the type, so that we can allow pa rallel use
of different formats for data of type address." (Quoted from <xref target="RFC1 of different formats for data of type address." (Quoted from <xref target="RFC1
034"/>, Section 2.2) 034" sectionFormat="comma" section="2.2"/>)
<!--End DNE text -->
In practice, the class for nearly every query is "IN" (the Internet). In practice, the class for nearly every query is "IN" (the Internet).
There are some queries for "CH" (the Chaos class), but they are usually for the purposes of There are some queries for "CH" (the Chaos class), but they are usually for the purposes of
information about the server itself rather than for a different type of address. information about the server itself rather than for a different type of address.
</t> </dd>
<dt>QNAME:</dt>
<t hangText='QNAME:'> <dd>
<iref item='QNAME'/> <iref item="QNAME" subitem="" primary="false"/>
The most commonly used rough definition is that the QNAME is a field in the Ques tion section of a The most commonly used rough definition is that the QNAME is a field in the Ques tion section of a
query. query.
<!--Begin DNE -->
"A standard query specifies a target domain name (QNAME), query type (QTYPE), an d query "A standard query specifies a target domain name (QNAME), query type (QTYPE), an d query
class (QCLASS) and asks for RRs which match." (Quoted from <xref target="RFC103 class (QCLASS) and asks for RRs which match." (Quoted from <xref target="RFC103
4"/>, Section 4" sectionFormat="comma" section="3.7.1"/>)
3.7.1) Strictly speaking, the definition comes from <xref target="RFC1035" sectionForma
<!--END DNE --> t="comma" section="4.1.2"/>, where the QNAME is defined in respect of the Questi
Strictly speaking, the definition comes from <xref target="RFC1035"/>, on
Section 4.1.2, where the QNAME is defined in respect of the Question section.
section. This definition appears to be applied consistently: the This definition appears to be applied consistently, as the discussion
discussion of inverse queries in Section 6.4.1 refers to the "owner name of inverse queries in <xref target="RFC1035" sectionFormat="of" section="6.4.1"/
of the query RR and its TTL", because inverse queries populate the > refers to the "owner name of
Answer section and leave the Question section empty. (Inverse queries the query RR and its TTL" because inverse queries populate the Answer section
are deprecated in <xref target="RFC3425"/>; thus, relevant and leave the Question section empty. (Inverse queries
are deprecated in <xref target="RFC3425" format="default"/>; thus, relevant
definitions do not appear in this document.) definitions do not appear in this document.)
</t> </dd>
<dt/>
<t> <dd>
However, <xref target="RFC2308"/> has an alternate definition that However, <xref target="RFC2308" format="default"/> has an alternate definition t
hat
puts the QNAME in the answer (or series of answers) instead of the puts the QNAME in the answer (or series of answers) instead of the
query. It defines QNAME as query. It defines QNAME as
<!--Begin DNE -->
"...the name in the query section of an "...the name in the query section of an
answer, or where this resolves to a CNAME, or CNAME chain, the data answer, or where this resolves to a CNAME, or CNAME chain, the data
field of the last CNAME. The last CNAME in this sense is that which field of the last CNAME. The last CNAME in this sense is that which
contains a value which does not resolve to another CNAME." contains a value which does not resolve to another CNAME."
<!--END DNE -->
This definition has a certain internal logic, because of the way CNAME This definition has a certain internal logic, because of the way CNAME
substitution works and the definition of CNAME. If a name server does substitution works and the definition of CNAME. If a name server does
not find an RRset that matches a query, but does find the same name in not find an RRset that matches a query, but does find the same name in
the same class with a CNAME record, then the name server "includes the the same class with a CNAME record, then the name server "includes the
CNAME record in the response and restarts the query at the domain name CNAME record in the response and restarts the query at the domain name
specified in the data field of the CNAME record." (Quoted from <xref specified in the data field of the CNAME record." (Quoted from <xref target="RFC
target="RFC1034"/>, Section 3.6.2) This is made explicit in the 1034" sectionFormat="comma" section="3.6.2"/>) This is made explicit in the
resolution algorithm outlined in Section 4.3.2 of <xref resolution algorithm outlined in <xref target="RFC1034" sectionFormat="of" secti
target="RFC1034"/>, which says to "change QNAME to the canonical name on="4.3.2"/>, which says to "change QNAME to the canonical name
in the CNAME RR, and go back to step 1" in the case of a CNAME RR. in the CNAME RR, and go back to step 1" in the case of a CNAME RR.
Since a CNAME record explicitly declares that the owner name is Since a CNAME record explicitly declares that the owner name is
canonically named what is in the RDATA, then there is a way to view canonically named what is in the RDATA, then there is a way to view
the new name (i.e., the name that was in the RDATA of the CNAME RR) as the new name (i.e., the name that was in the RDATA of the CNAME RR) as
also being the QNAME. also being the QNAME.
</t> </dd>
<dt/>
<t> <dd>
However, this creates confusion because the response to a However, this creates confusion because the response to a
query that results in CNAME processing contains in the echoed Question query that results in CNAME processing contains in the echoed Question
section one QNAME (the name in the original query) and a second QNAME section one QNAME (the name in the original query) and a second QNAME
that is in the data field of the last CNAME. The confusion comes from that is in the data field of the last CNAME. The confusion comes from
the iterative/recursive mode of resolution, which finally returns an the iterative/recursive mode of resolution, which finally returns an
answer that need not actually have the same owner name as the QNAME answer that need not actually have the same owner name as the QNAME
contained in the original query. contained in the original query.
</t> </dd>
<dt/>
<t> <dd>
<t>
To address this potential confusion, it is helpful to distinguish To address this potential confusion, it is helpful to distinguish
between three meanings: between three meanings:
<list style="symbols">
<t>
QNAME (original): The name actually sent in the Question section in the original
query, which is
always echoed in the (final) reply in the Question section when the QR bit is se
t to 1.
</t> </t>
<t> <dl>
QNAME (effective): A name actually resolved, which is either the name originally <dt>QNAME (original):</dt><dd>The name actually sent in the Question section in
queried the original query, which is
always echoed in the (final) reply in the Question section when the QR bit is se
t to 1.
</dd>
<dt>QNAME (effective):</dt><dd>A name actually resolved, which is either the nam
e originally queried
or a name received in a CNAME chain response. or a name received in a CNAME chain response.
</t> </dd>
<t>
QNAME (final): The name actually resolved, which is either the name actually que
ried or else
the last name in a CNAME chain response.
</t>
</list></t>
<t>Note that, because the definition in <xref target="RFC2308"/> is <dt>QNAME (final):</dt><dd>The name actually resolved, which is either the name
actually for a different concept than what was in <xref actually queried or else
target="RFC1034"/>, it would have been better if <xref the last name in a CNAME chain response.
target="RFC2308"/> had used a different name for that concept. In </dd>
</dl>
</dd>
<dt/>
<dd>Note that, because the definition in <xref target="RFC2308" format="
default"/> is
actually for a different concept than what was in <xref target="RFC1034" format=
"default"/>, it would have been better if <xref target="RFC2308" format="default
"/> had used a different name for that concept. In
general use today, QNAME almost always means what is defined above as general use today, QNAME almost always means what is defined above as
"QNAME (original)".</t> "QNAME (original)".</dd>
<dt>Referrals:</dt>
<t hangText='Referrals:'> <dd>
<iref item='Referrals'/> <iref item="Referrals" subitem="" primary="false"/>
A type of response in which a server, signaling that it is not A type of response in which a server, signaling that it is not
(completely) authoritative for an answer, provides the querying (completely) authoritative for an answer, provides the querying
resolver with an alternative place to send its query. Referrals can resolver with an alternative place to send its query. Referrals can
be partial.</t> be partial.</dd>
<dt/>
<t>A referral arises when a server is not performing recursive service <dd>A referral arises when a server is not performing recursive service
while answering a query. It appears in step 3(b) of the algorithm in while answering a query. It appears in step 3(b) of the algorithm in
<xref target="RFC1034" />, Section 4.3.2.</t> <xref target="RFC1034" sectionFormat="comma" section="4.3.2"/>.</dd>
<dt/>
<t>There are two types of referral response. The first is a downward <dd>There are two types of referral response. The first is a downward
referral (sometimes described as "delegation response"), where the referral (sometimes described as "delegation response"), where the
server is authoritative for some portion of the QNAME. The authority server is authoritative for some portion of the QNAME. The Authority
section RRset's RDATA contains the name servers specified at the section RRset's RDATA contains the name servers specified at the
referred-to zone cut. In normal DNS operation, this kind of response referred-to zone cut. In normal DNS operation, this kind of response
is required in order to find names beneath a delegation. The bare is required in order to find names beneath a delegation. The bare
use of "referral" means this kind of referral, and many people believe use of "referral" means this kind of referral, and many people believe
that this is the only legitimate kind of referral in the DNS.</t> that this is the only legitimate kind of referral in the DNS.</dd>
<dt/>
<t>The second is an upward referral (sometimes described as "root <dd>The second is an upward referral (sometimes described as "root
referral"), where the server is not authoritative for any portion of referral"), where the server is not authoritative for any portion of
the QNAME. When this happens, the referred-to zone in the authority the QNAME. When this happens, the referred-to zone in the Authority
section is usually the root zone ("."). In normal DNS operation, this section is usually the root zone ("."). In normal DNS operation, this
kind of response is not required for resolution or for correctly kind of response is not required for resolution or for correctly
answering any query. There is no requirement that any server send answering any query. There is no requirement that any server send
upward referrals. Some people regard upward referrals as a sign of a upward referrals. Some people regard upward referrals as a sign of a
misconfiguration or error. Upward referrals always need some sort of misconfiguration or error. Upward referrals always need some sort of
qualifier (such as "upward" or "root") and are never identified simply by qualifier (such as "upward" or "root") and are never identified simply by
the word "referral".</t> the word "referral".</dd>
<dt/>
<t>A response that has only a referral contains an empty answer <dd>A response that has only a referral contains an empty Answer
section. It contains the NS RRset for the referred-to zone in the section. It contains the NS RRset for the referred-to zone in the
Authority section. It may contain RRs that provide addresses in the Authority section. It may contain RRs that provide addresses in the
additional section. The AA bit is clear.</t> Additional section. The AA bit is clear.</dd>
<dt/>
<t>In the case where the query matches an alias, and the server is not <dd>In the case where the query matches an alias, and the server is not
authoritative for the target of the alias but is authoritative for authoritative for the target of the alias but is authoritative for
some name above the target of the alias, the resolution algorithm will some name above the target of the alias, the resolution algorithm will
produce a response that contains both the authoritative answer for the produce a response that contains both the authoritative answer for the
alias and a referral. Such a partial answer and referral alias and a referral. Such a partial answer and referral
response has data in the Answer section. It has the NS RRset for the response has data in the Answer section. It has the NS RRset for the
referred-to zone in the Authority section. It may contain RRs that referred-to zone in the Authority section. It may contain RRs that
provide addresses in the additional section. The AA bit is set, provide addresses in the Additional section. The AA bit is set
because the first name in the Answer section matches the QNAME and the because the first name in the Answer section matches the QNAME and the
server is authoritative for that answer (see <xref target="RFC1035"/>, server is authoritative for that answer (see <xref target="RFC1035" sectionForma
Section 4.1.1).</t> t="comma" section="4.1.1"/>).</dd>
</dl>
</list></t> </section>
</section> <section anchor="rrs" numbered="true" toc="default">
<name>Resource Records</name>
<section anchor="rrs" title="Resource Records"> <dl newline="false" spacing="normal">
<t><list style="hanging"> <dt>RR:</dt>
<dd>
<t hangText='RR:'> <iref item="RR" subitem="" primary="false"/>
<iref item='RR'/> An acronym for resource record. (See <xref target="RFC1034" sectionFormat="comm
An acronym for resource record. (See <xref target="RFC1034"/>, Section 3.6.)</t a" section="3.6"/>.)</dd>
> <dt>RRset:</dt>
<dd>
<t hangText='RRset:'> <iref item="RRset" subitem="" primary="false"/>
<iref item='RRset'/>
A set of resource records "with the same label, class and type, but with differe nt A set of resource records "with the same label, class and type, but with differe nt
data" (according to <xref target="RFC2181"/>, Section 5). Also written as "RRSe t" in some documents. As a clarification, data" (according to <xref target="RFC2181" sectionFormat="comma" section="5"/>). Also written as "RRSet" in some documents. As a clarification,
"same label" in this definition means "same owner name". "same label" in this definition means "same owner name".
In addition, <xref target="RFC2181"/> states that "the TTLs of all RRs in an RRS In addition, <xref target="RFC2181" format="default"/> states that "the TTLs of
et must be the same". all RRs in an RRSet must be the same".
</t> </dd>
<dt/>
<dd>
<t>Note that RRSIG resource records do not match this definition.
<xref target="RFC4035" format="default"/> says:</t></dd>
<t>Note that RRSIG resource records do not match this definition. <dt/><dd>
<xref target="RFC4035"/> says: <dl><dt/><dd>
<list style="empty"><t> "An RRset <bcp14>MAY</bcp14> have multiple RRSIG RRs associated with it. Note th
<!--Begin DNE --> at
An RRset MAY have multiple RRSIG RRs associated with it. Note that
as RRSIG RRs are closely tied to the RRsets whose signatures they as RRSIG RRs are closely tied to the RRsets whose signatures they
contain, RRSIG RRs, unlike all other DNS RR types, do not form contain, RRSIG RRs, unlike all other DNS RR types, do not form
RRsets. In particular, the TTL values among RRSIG RRs with a common RRsets. In particular, the TTL values among RRSIG RRs with a common
owner name do not follow the RRset rules described in <xref target="RFC2181"/>.< owner name do not follow the RRset rules described in <xref target="RFC2181" for
/t></list> mat="default"/>."</dd>
<!--End DNE --> </dl>
<t>
</t> </t>
</dd>
<t hangText='Master file:'> <dt>Master file:</dt>
<iref item='Master file'/> <dd>
<iref item="Master file" subitem="" primary="false"/>
<!--Begin DNE -->
"Master files are text files that contain RRs in text form. Since the contents of a zone "Master files are text files that contain RRs in text form. Since the contents of a zone
can be expressed in the form of a list of RRs a master file is most often used t o define a can be expressed in the form of a list of RRs a master file is most often used t o define a
zone, though it can be used to list a cache's contents." (Quoted from <xref tar zone, though it can be used to list a cache's contents." (Quoted from <xref tar
get="RFC1035"/>, get="RFC1035" sectionFormat="comma" section="5"/>)
Section 5) Master files are sometimes called "zone files".</dd>
<dt>Presentation format:</dt>
<!--End DNE --> <dd>
Master files are sometimes called "zone files".</t> <iref item="Presentation format" subitem="" primary="false"/>
<t hangText='Presentation format:'>
<iref item='Presentation format'/>
The text format used in master files. This format is shown but not formally defi ned in The text format used in master files. This format is shown but not formally defi ned in
<xref target="RFC1034"/> or <xref target="RFC1035"/>. The term "presentation for <xref target="RFC1034" format="default"/> or <xref target="RFC1035" format="defa
mat" ult"/>. The term "presentation format"
first appears in <xref target="RFC4034"/>.</t> first appears in <xref target="RFC4034" format="default"/>.</dd>
<dt>EDNS:</dt>
<t hangText='EDNS:'> <dd>
<iref item='EDNS'/> <iref item="EDNS" subitem="" primary="false"/>
The extension mechanisms for DNS, defined in <xref The extension mechanisms for DNS, defined in <xref target="RFC6891" format="defa
target="RFC6891"/>. Sometimes called "EDNS0" or "EDNS(0)" ult"/>. Sometimes called "EDNS0" or "EDNS(0)"
to indicate the version number. EDNS allows DNS clients and servers to specify m to indicate the version number.
essage EDNS allows DNS clients and servers to specify message
sizes larger than the original 512 octet limit, to expand the response code spac sizes larger than the original 512-octet limit, to expand the response code spac
e and e, and
to carry additional options that affect the handling of a DNS query.</t> to carry additional options that affect the handling of a DNS query.</dd>
<dt>OPT:</dt>
<t hangText='OPT:'> <dd>
<iref item='OPT'/> <iref item="OPT" subitem="" primary="false"/>
A pseudo-RR (sometimes called a "meta-RR") that is used only to contain A pseudo-RR (sometimes called a "meta-RR") that is used only to contain
control information pertaining to the question-and-answer sequence of a specific control information pertaining to the question-and-answer sequence of a specific
transaction. (Definition paraphrased from <xref target="RFC6891"/>, Section 6.1. transaction. (Definition paraphrased from <xref target="RFC6891" sectionFormat="
1.) comma" section="6.1.1"/>.) It is used by EDNS.</dd>
It is used by EDNS.</t> <dt>Owner:</dt>
<dd>
<t hangText='Owner:'> <iref item="Owner" subitem="" primary="false"/>
<iref item='Owner'/> "The domain name where the RR is found." (Quoted from <xref target="RFC1034" se
"The domain name where the RR is found." (Quoted from <xref target="RFC1034"/>, ctionFormat="comma" section="3.6"/>) Often appears in the term "owner name".</d
Section 3.6) Often appears in the term "owner name".</t> d>
<dt>SOA field names:</dt>
<t hangText='SOA field names:'> <dd>
<iref item='SOA field names'/> <iref item="SOA field names" subitem="" primary="false"/>
<iref item='SOA'/> <iref item="SOA" subitem="" primary="false"/>
DNS documents, including the definitions here, often refer to the fields in the DNS documents, including the definitions here, often refer to the fields in the
RDATA of an SOA resource record by field name. RDATA of an SOA resource record by field name.
"SOA" stands for "start of a zone of authority". "SOA" stands for "start of a zone of authority".
Those fields are defined in Section 3.3.13 of <xref target="RFC1035"/>. Those fields are defined in <xref target="RFC1035" sectionFormat="of" section="3 .3.13"/>.
The names (in the order they appear in the SOA RDATA) are MNAME, RNAME, SERIAL, REFRESH, RETRY, The names (in the order they appear in the SOA RDATA) are MNAME, RNAME, SERIAL, REFRESH, RETRY,
EXPIRE, and MINIMUM. EXPIRE, and MINIMUM.
Note that the meaning of the MINIMUM field is updated in Section 4 of <xref targ et="RFC2308"/>; the new definition Note that the meaning of the MINIMUM field is updated in <xref target="RFC2308" sectionFormat="of" section="4"/>; the new definition
is that the MINIMUM field is only "the TTL to be used for negative responses". is that the MINIMUM field is only "the TTL to be used for negative responses".
This document tends to use field names instead of terms that describe the fields This document tends to use field names instead of terms that describe the fields
.</t> .</dd>
<dt>TTL:</dt>
<t hangText='TTL:'> <dd>
<iref item='TTL'/> <iref item="TTL" subitem="" primary="false"/>
The maximum "time to live" of a resource record. The maximum "time to live" of a resource record.
<!--Begin DNE -->
"A TTL value is an unsigned "A TTL value is an unsigned
number, with a minimum value of 0, and a maximum value of 2147483647. That is, a number, with a minimum value of 0, and a maximum value of 2147483647. That is, a
maximum of 2^31 - 1. When transmitted, this value shall be encoded in the less maximum of 2^31 - 1. When transmitted, this value shall be encoded in the less
significant 31 bits of the 32 bit TTL field, with the most significant, or sign, significant 31 bits of the 32 bit TTL field, with the most significant, or sign,
bit set to zero." (Quoted from <xref target="RFC2181"/>, Section 8) bit set to zero." (Quoted from <xref target="RFC2181" sectionFormat="comma" sec
<!--End DNE --> tion="8"/>)
(Note that <xref target="RFC1035"/> Note that <xref target="RFC1035" format="default"/>
erroneously stated that this is a signed integer; that was fixed by <xref target erroneously stated that this is a signed integer; that was fixed by <xref target
="RFC2181"/>.)</t> ="RFC2181" format="default"/>.</dd>
<dt/>
<t>The TTL "specifies the time interval that the resource record may be cached <dd>The TTL "specifies the time interval that the resource record may be
cached
before the source of the information should again be consulted." (Quoted from before the source of the information should again be consulted." (Quoted from
<xref target="RFC1035"/>, Section 3.2.1) Section 4.1.3 of the same document sta tes: "the time interval (in seconds) that the resource <xref target="RFC1035" sectionFormat="comma" section="3.2.1"/>) <xref target="RF C1035" sectionFormat="of" section="4.1.3"/> states "the time interval (in second s) that the resource
record may be cached before it should be discarded". Despite being defined for a resource record, the TTL of every record may be cached before it should be discarded". Despite being defined for a resource record, the TTL of every
resource record in an RRset is required to be the same (<xref target="RFC2181"/> resource record in an RRset is required to be the same (<xref target="RFC2181" s
, Section 5.2).</t> ectionFormat="comma" section="5.2"/>).</dd>
<dt/>
<t>The reason that the TTL is the maximum time to live is that a cache operator <dd>The reason that the TTL is the maximum time to live is that a cache
might decide to shorten the time to live for operational purposes, such as if operator
might decide to shorten the time to live for operational purposes, for example,
if
there is a policy to disallow TTL values over a certain number. there is a policy to disallow TTL values over a certain number.
Some servers are known to ignore the TTL on some RRsets (such as when the author itative data Some servers are known to ignore the TTL on some RRsets (such as when the author itative data
has a very short TTL) even though this is against the advice in RFC 1035. has a very short TTL) even though this is against the advice in <xref target="RF C1035"/>.
An RRset can be flushed from the cache before the end of the TTL interval, An RRset can be flushed from the cache before the end of the TTL interval,
at which point, the value of the TTL becomes unknown because the RRset at which point, the value of the TTL becomes unknown because the RRset
with which it was associated no longer exists.</t> with which it was associated no longer exists.</dd>
<dt/>
<t>There is also the concept of a "default TTL" for a zone, which can be a confi <dd>There is also the concept of a "default TTL" for a zone, which can b
guration e a configuration
parameter in the server software. This is often expressed by a default for the parameter in the server software. This is often expressed by a default for the
entire server, and a default for a zone using the $TTL directive entire server, and a default for a zone using the $TTL directive
in a zone file. The $TTL directive was added to the master file in a zone file. The $TTL directive was added to the master file
format by <xref target="RFC2308"/>.</t> format by <xref target="RFC2308" format="default"/>.</dd>
<dt>Class independent:</dt>
<t hangText='Class independent:'> <dd>
<iref item='Class independent'/> <iref item="Class independent" subitem="" primary="false"/>
A resource record type whose syntax and semantics are the same for every DNS A resource record type whose syntax and semantics are the same for every DNS
class. A resource record type that is not class independent has different meanin class.
gs depending on the A resource record type that is not class independent has different meanings, dep
DNS class of the record, or the meaning is undefined for some class. ending on the
DNS class of the record or if the meaning is undefined for some classes.
Most resource record types are defined for class 1 (IN, the Internet), Most resource record types are defined for class 1 (IN, the Internet),
but many are undefined for other classes.</t> but many are undefined for other classes.</dd>
<dt>Address records:</dt>
<t hangText='Address records:'> <dd>
<iref item='Address records'/> <iref item="Address records" subitem="" primary="false"/>
Records whose type is A or AAAA. Records whose type is either A or AAAA.
<xref target="RFC2181"/> informally defines these as "(A, AAAA, etc)". <xref target="RFC2181" format="default"/> informally defines these as "(A, AAAA,
Note that new types of address records could be defined in the future.</t> etc)".
Note that new types of address records could be defined in the future.</dd>
</list></t> </dl>
</section> </section>
<section anchor="dns-servers-and-clients" numbered="true" toc="default">
<section anchor="dns-servers-and-clients" title="DNS Servers and Clients"> <name>DNS Servers and Clients</name>
<t>This section defines the terms used for the systems that act as DNS
<t>This section defines the terms used for the systems that act as DNS
clients, DNS servers, or both. In past RFCs, DNS servers are clients, DNS servers, or both. In past RFCs, DNS servers are
sometimes called "name servers", "nameservers", or just sometimes called "name servers", "nameservers", or just
"servers". There is no formal definition of "DNS server", but RFCs "servers". There is no formal definition of "DNS server", but RFCs
generally assume that it is an Internet server that listens for generally assume that it is an Internet server that listens for
queries and sends responses using the DNS protocol defined in <xref queries and sends responses using the DNS protocol defined in <xref target="RFC1
target="RFC1035"/> and its successors.</t> 035" format="default"/> and its successors.</t>
<t>It is important to note that the terms "DNS server" and "name
<t>It is important to note that the terms "DNS server" and "name
server" require context in order to understand the services being server" require context in order to understand the services being
provided. Both authoritative servers and recursive resolvers are often provided. Both authoritative servers and recursive resolvers are often
called "DNS servers" and "name servers" even though they serve called "DNS servers" and "name servers" even though they serve
different roles (but may be part of the same software package).</t> different roles (but may be part of the same software package).</t>
<t>For terminology specific to the global DNS root server system, see
<t>For terminology specific to the global DNS root server system, see <xref target="RSSAC026" format="default"/>. That document defines terms such as
<xref target="RSSAC026"/>. That document defines terms such as "root "root
server", "root server operator", and terms that are specific to the server", "root server operator", and terms that are specific to the
way that the root zone of the global DNS is served.</t> way that the root zone of the global DNS is served.</t>
<dl newline="false" spacing="normal">
<t><list style="hanging"> <dt>Resolver:</dt>
<dd>
<t hangText='Resolver:'> <iref item="Resolver" subitem="" primary="false"/>
<iref item='Resolver'/>
A program "that extract[s] information from name A program "that extract[s] information from name
servers in response to client requests." (Quoted from <xref target="RFC1034"/>, Section 2.4) A resolver performs servers in response to client requests." (Quoted from <xref target="RFC1034" se ctionFormat="comma" section="2.4"/>) A resolver performs
queries for a name, type, and class, and receives responses. The queries for a name, type, and class, and receives responses. The
logical function is called "resolution". In practice, the term is logical function is called "resolution". In practice, the term is
usually referring to some specific type of resolver usually referring to some specific type of resolver
(some of which are defined below), and understanding (some of which are defined below), and understanding
the use of the term depends on understanding the context.</t> the use of the term depends on understanding the context.</dd>
<dt/>
<t>A related term is "resolve", which is not formally defined in <xref target="R <dd>A related term is "resolve", which is not formally defined in <xref
FC1034"/> target="RFC1034" format="default"/>
or <xref target="RFC1035"/>. An imputed definition might be "asking a question t or <xref target="RFC1035" format="default"/>. An imputed definition might be "as
hat king a question that
consists of a domain name, class, and type, and receiving some sort of response" . consists of a domain name, class, and type, and receiving some sort of response" .
Similarly, an imputed definition of "resolution" might be "the response received Similarly, an imputed definition of "resolution" might be "the response received
from resolving".</t> from resolving".</dd>
<dt>Stub resolver:</dt>
<t hangText='Stub resolver:'> <dd>
<iref item='Stub resolver'/> <iref item="Stub resolver" subitem="" primary="false"/>
A resolver that cannot perform all resolution A resolver that cannot perform all resolution
itself. Stub resolvers generally depend on a recursive resolver to undertake the itself. Stub resolvers generally depend on a recursive resolver to undertake the
actual resolution function. Stub resolvers are discussed but never actual resolution function. Stub resolvers are discussed but never
fully defined in Section 5.3.1 of <xref target="RFC1034"/>. fully defined in <xref target="RFC1034" sectionFormat="of" section="5.3.1"/>.
They are fully defined in Section 6.1.3.1 of <xref target="RFC1123"/>.</t> They are fully defined in <xref target="RFC1123" sectionFormat="of" section="6.1
.3.1"/>.</dd>
<t hangText='Iterative mode:'> <dt>Iterative mode:</dt>
<iref item='Iterative mode'/> <dd>
<iref item="Iterative mode" subitem="" primary="false"/>
A resolution mode of a server that receives DNS A resolution mode of a server that receives DNS
queries and responds with a referral to another server. Section 2.3 of <xref ta rget="RFC1034"/> queries and responds with a referral to another server. <xref target="RFC1034" s ectionFormat="of" section="2.3"/>
describes this as "The server refers the client to describes this as "The server refers the client to
another server and lets the client pursue the query." another server and lets the client pursue the query."
A resolver that works in iterative mode is sometimes called an "iterative A resolver that works in iterative mode is sometimes called an "iterative
resolver". resolver".
See also "iterative resolution" later in this section.</t> See also "iterative resolution" later in this section.</dd>
<dt>Recursive mode:</dt>
<t hangText='Recursive mode:'> <dd>
<iref item='Recursive mode'/> <t><iref item="Recursive mode" subitem="" primary="false"/>
A resolution mode of a server that receives DNS A resolution mode of a server that receives DNS
queries and either responds to those queries from a local cache or queries and either responds to those queries from a local cache or
sends queries to other servers in order to get the final answers to sends queries to other servers in order to get the final answers to
the original queries. Section 2.3 of <xref target="RFC1034"/> describes this as "the the original queries. <xref target="RFC1034" sectionFormat="of" section="2.3"/> describes this as "the
first server pursues the query for the client at another server". first server pursues the query for the client at another server".
Section 4.3.1 of <xref target="RFC1034"/> says: "in [recursive] <xref target="RFC1034" sectionFormat="of" section="4.3.1"/> says: "in [recursive ]
mode the name server acts in the role of a resolver and mode the name server acts in the role of a resolver and
returns either an error or the answer, but never referrals." returns either an error or the answer, but never referrals."
That same section also says: That same section also says:
<list style="empty"> </t>
<!--Begin DNE --> <dl spacing="normal">
<t>The recursive mode occurs when a query with RD set arrives at a server <dt/><dd>"The recursive mode occurs when a query with RD set arrives at a serv
er
which is willing to provide recursive service; the client can verify that recurs ive mode was used by which is willing to provide recursive service; the client can verify that recurs ive mode was used by
checking that both RA and RD are set in the reply.</t></list></t> checking that both RA and RD are set in the reply."</dd>
<!--End DNE --> </dl>
</dd>
<t>A server operating in recursive mode may be thought of as having a name <dt/>
<dd>A server operating in recursive mode may be thought of as having a n
ame
server side (which is what answers the query) and a resolver side server side (which is what answers the query) and a resolver side
(which performs the resolution function). Systems operating (which performs the resolution function). Systems operating
in this mode are commonly called "recursive servers". Sometimes they in this mode are commonly called "recursive servers". Sometimes they
are called "recursive resolvers". In practice, it is not possible to know are called "recursive resolvers". In practice, it is not possible to know
in advance whether the server that one is querying will also perform in advance whether the server that one is querying will also perform
recursion; both terms can be observed in use interchangeably.</t> recursion; both terms can be observed in use interchangeably.</dd>
<dt>Recursive resolver:</dt>
<t hangText='Recursive resolver:'> <dd>
<iref item='Recursive resolver'/> <iref item="Recursive resolver" subitem="" primary="false"/>
A resolver that acts in recursive mode. A resolver that acts in recursive mode.
In general, a recursive resolver is expected to cache the answers it receives In general, a recursive resolver is expected to cache the answers it receives
(which would make it a full-service resolver), but some recursive resolvers migh (which would make it a full-service resolver), but some recursive resolvers migh
t not cache.</t> t not cache.</dd>
<dt/>
<t><xref target="RFC4697"/> tried to differentiate between a <dd>
recursive resolver and an iterative resolver.</t> <xref target="RFC4697" format="default"/> tried to differentiate betwe
en a
<t hangText='Recursive query:'> recursive resolver and an iterative resolver.</dd>
<iref item='Recursive query'/> <dt>Recursive query:</dt>
A query with the Recursion Desired (RD) bit set to 1 in the header. (See Section <dd>
4.1.1 of <xref <iref item="Recursive query" subitem="" primary="false"/>
target="RFC1035"/>.) If recursive service is available and is requested by the R A query with the Recursion Desired (RD) bit set to 1 in the header. (See <xref t
D bit in the query, arget="RFC1035" sectionFormat="of" section="4.1.1"/>.) If recursive service is a
the server uses its resolver to answer the query. (See Section 4.3.2 of <xref ta vailable and is requested by the RD bit in the query,
rget="RFC1034"/>.)</t> the server uses its resolver to answer the query. (See <xref target="RFC1034" se
ctionFormat="of" section="4.3.2"/>.)</dd>
<t hangText='Non-recursive query:'> <dt>Non-recursive query:</dt>
<iref item='Non-recursive query'/> <dd>
<iref item="Non-recursive query" subitem="" primary="false"/>
A query with the Recursion Desired (RD) bit set to 0 in the header. A server can answer A query with the Recursion Desired (RD) bit set to 0 in the header. A server can answer
non-recursive queries using only local information: the response contains either an error, the non-recursive queries using only local information: the response contains either an error, the
answer, or a referral to some other server "closer" to the answer. answer, or a referral to some other server "closer" to the answer.
(See Section 4.3.1 of <xref target="RFC1034"/>.)</t> (See <xref target="RFC1034" sectionFormat="of" section="4.3.1"/>.)</dd>
<dt>Iterative resolution:</dt>
<t hangText='Iterative resolution:'> <dd>
<iref item='Iterative resolution'/> <iref item="Iterative resolution" subitem="" primary="false"/>
A name server may be presented with a query that can only be answered by some ot her server. The two A name server may be presented with a query that can only be answered by some ot her server. The two
general approaches to dealing with this problem are "recursive", in which the fi rst server pursues general approaches to dealing with this problem are "recursive", in which the fi rst server pursues
the query on behalf of the client at another server, and "iterative", in which t he server refers the client the query on behalf of the client at another server, and "iterative", in which t he server refers the client
to another server and lets the client pursue the query there. (See Section 2.3 o to another server and lets the client pursue the query there. (See <xref target=
f <xref "RFC1034" sectionFormat="of" section="2.3"/>.)</dd>
target="RFC1034"/>.)</t> <dt/>
<dd>In iterative resolution, the client repeatedly makes non-recursive q
<t>In iterative resolution, the client repeatedly makes non-recursive queries an ueries and follows referrals
d follows referrals and/or aliases. The iterative resolution algorithm is described in <xref target=
and/or aliases. The iterative resolution algorithm is described in Section 5.3.3 "RFC1034" sectionFormat="of" section="5.3.3"/>.</dd>
of <xref <dt>Full resolver:</dt>
target="RFC1034"/>.</t> <dd>
<iref item="Full resolver" subitem="" primary="false"/>
<t hangText='Full resolver:'> This term is used in <xref target="RFC1035" format="default"/>, but it is not de
<iref item='Full resolver'/> fined there. RFC
This term is used in <xref target="RFC1035"/>, but it is not defined there. RFC
1123 defines a "full-service resolver" that may or may not be what was intended 1123 defines a "full-service resolver" that may or may not be what was intended
by "full resolver" in <xref target="RFC1035"/>. by "full resolver" in <xref target="RFC1035" format="default"/>.
This term is not properly defined in any RFC, and there is no consensus on what the term means. This term is not properly defined in any RFC, and there is no consensus on what the term means.
The use of this term without proper context is discouraged.</t> The use of this term without proper context is discouraged.</dd>
<dt>Full-service resolver:</dt>
<t hangText='Full-service resolver:'> <dd>
<iref item='Full-service resolver'/> <iref item="Full-service resolver" subitem="" primary="false"/>
Section 6.1.3.1 of <xref target="RFC1123"/> defines this term <xref target="RFC1123" sectionFormat="of" section="6.1.3.1"/> defines this term
to mean a resolver that acts in recursive mode with a cache (and meets as a resolver that acts in recursive mode with a cache (and meets
other requirements).</t> other requirements).</dd>
<dt>Priming:</dt>
<t hangText='Priming:'> <dd>
<iref item='Priming'/> <iref item="Priming" subitem="" primary="false"/>
"The act of finding the list of root servers from a "The act of finding the list of root servers from a
configuration that lists some or all of the purported IP addresses of configuration that lists some or all of the purported IP addresses of
some or all of those root servers." (Quoted from <xref target="RFC8109"/>, Secti on 2) some or all of those root servers." (Quoted from <xref target="RFC8109" sectionF ormat="comma" section="2"/>)
In order to operate in recursive mode, a resolver needs to know the address of a t least one root server. In order to operate in recursive mode, a resolver needs to know the address of a t least one root server.
Priming is most often done from a configuration setting that contains a Priming is most often done from a configuration setting that contains a
list of authoritative servers for the root zone.</t> list of authoritative servers for the root zone.</dd>
<dt>Root hints:</dt>
<t hangText='Root hints:'> <dd>
<iref item='Root hints'/>"Operators who manage a DNS recursive resolver typicall <iref item="Root hints" subitem="" primary="false"/>"Operators who man
y need to configure age a DNS recursive resolver typically need to configure
a 'root hints file'. a 'root hints file'.
This file contains the names and IP addresses of the authoritative name servers This file contains the names and IP addresses of the authoritative name servers
for the root zone, so the software can bootstrap the DNS resolution process. for the root zone, so the software can bootstrap the DNS resolution process.
For many pieces of software, this list comes built into the software." (Quoted For many pieces of software, this list comes built into the software." (Quoted
from <xref target="IANA_RootFiles"/>) from <xref target="IANA_RootFiles" format="default"/>)
This file is often used in priming.</t> This file is often used in priming.</dd>
<dt>Negative caching:</dt>
<t hangText='Negative caching:'> <dd>
<iref item='Negative caching'/> <iref item="Negative caching" subitem="" primary="false"/>
"The storage of knowledge that something does not exist, cannot "The storage of knowledge that something does not exist, cannot
or does not give an answer." (Quoted from <xref target="RFC2308"/>, Section 1)</ or does not give an answer." (Quoted from <xref target="RFC2308" sectionFormat="
t> comma" section="1"/>)</dd>
<dt>Authoritative server:</dt>
<t hangText='Authoritative server:'> <dd>
<iref item='Authoritative server'/> <iref item="Authoritative server" subitem="" primary="false"/>
<iref item='NS'/> <iref item="NS" subitem="" primary="false"/>
"A server that knows the content of a DNS zone from local knowledge, and thus ca n answer "A server that knows the content of a DNS zone from local knowledge, and thus ca n answer
queries about that zone without needing to query other servers." (Quoted from <x ref target="RFC2182"/>, Section 2) queries about that zone without needing to query other servers." (Quoted from <x ref target="RFC2182" sectionFormat="comma" section="2"/>)
An authoritative server is named in the NS ("name server") record in a zone. An authoritative server is named in the NS ("name server") record in a zone.
It is a system that responds to DNS queries with information about It is a system that responds to DNS queries with information about
zones for which it has been configured to answer with the AA flag in zones for which it has been configured to answer with the AA flag in
the response header set to 1. It is a server that has authority over the response header set to 1. It is a server that has authority over
one or more DNS zones. Note that it is possible for an authoritative one or more DNS zones. Note that it is possible for an authoritative
server to respond to a query without the parent zone delegating server to respond to a query without the parent zone delegating
authority to that server. Authoritative servers also provide authority to that server. Authoritative servers also provide
"referrals", usually to child zones delegated from them; these "referrals", usually to child zones delegated from them; these
referrals have the AA bit set to 0 and come with referral data in the referrals have the AA bit set to 0 and come with referral data in the
Authority and (if needed) the Additional sections.</t> Authority and (if needed) the Additional sections.</dd>
<dt>Authoritative-only server:</dt>
<t hangText='Authoritative-only server:'> <dd>
<iref item='Authoritative-only server'/> <iref item="Authoritative-only server" subitem="" primary="false"/>
A name server that only serves authoritative data and ignores requests for recur sion. A name server that only serves authoritative data and ignores requests for recur sion.
It will "not normally generate any queries of its own. Instead it answers non-r ecursive It will "not normally generate any queries of its own. Instead it answers non-r ecursive
queries from iterative resolvers looking for information in zones it serves." ( Quoted from <xref target="RFC4697"/>, Section 2.4) queries from iterative resolvers looking for information in zones it serves." ( Quoted from <xref target="RFC4697" sectionFormat="comma" section="2.4"/>)
In this case, "ignores requests for recursion" means "responds to requests for In this case, "ignores requests for recursion" means "responds to requests for
recursion with responses indicating that recursion was not performed".</t> recursion with responses indicating that recursion was not performed".</dd>
<dt>Zone transfer:</dt>
<t hangText='Zone transfer:'> <dd>
<iref item='Zone transfer'/> <iref item="Zone transfer" subitem="" primary="false"/>
The act of a client requesting a copy of a zone and an authoritative server The act of a client requesting a copy of a zone and an authoritative server
sending the needed information. sending the needed information.
(See <xref target="zones"/> for a description of zones.) (See <xref target="zones" format="default"/> for a description of zones.)
There are two common standard ways to do zone transfers: There are two common standard ways to do zone transfers:
the AXFR ("Authoritative Transfer") mechanism to copy the full zone (described i the AXFR ("Authoritative Transfer") mechanism to copy the full zone (described i
n <xref target="RFC5936"/>, and n <xref target="RFC5936" format="default"/>, and
the IXFR ("Incremental Transfer") mechanism to copy only parts of the zone that the IXFR ("Incremental Transfer") mechanism to copy only parts of the zone that
have changed (described in <xref target="RFC1995"/>). have changed (described in <xref target="RFC1995" format="default"/>).
Many systems use non-standard methods for zone transfer outside the DNS protocol Many systems use non-standard methods for zone transfers outside the DNS protoco
.</t> l.</dd>
<dt>Slave server:</dt>
<t hangText='Slave server:'> <dd>
<iref item='Slave server'/> <iref item="Slave server" subitem="" primary="false"/>
See "Secondary server".</t> See "Secondary server".</dd>
<dt>Secondary server:</dt>
<t hangText='Secondary server:'> <dd>
<iref item='Secondary server'/> <iref item="Secondary server" subitem="" primary="false"/>
"An authoritative server which uses zone transfer to retrieve the "An authoritative server which uses zone transfer to retrieve the
zone." (Quoted from <xref target="RFC1996"/>, Section 2.1) zone." (Quoted from <xref target="RFC1996" sectionFormat="comma" section="2.1"/>
Secondary servers are also discussed in <xref target="RFC1034"/>. )
<xref target="RFC2182"/> describes secondary servers in Secondary servers are also discussed in <xref target="RFC1034" format="default"/
more detail. Although early DNS RFCs such as <xref target="RFC1996"/> referred >.
to this as a "slave", the <xref target="RFC2182" format="default"/> describes secondary servers in
more detail. Although early DNS RFCs such as <xref target="RFC1996" format="def
ault"/> referred to this as a "slave", the
current common usage has shifted to calling it a "secondary". current common usage has shifted to calling it a "secondary".
</t> </dd>
<dt>Master server:</dt>
<t hangText='Master server:'> <dd>
<iref item='Master server'/> <iref item="Master server" subitem="" primary="false"/>
See "Primary server".</t> See "Primary server".</dd>
<dt>Primary server:</dt>
<t hangText='Primary server:'> <dd>
<iref item='Primary server'/> <iref item="Primary server" subitem="" primary="false"/>
"Any authoritative server configured to be the source of zone transfer "Any authoritative server configured to be the source of zone transfer
for one or more [secondary] servers." (Quoted from <xref target="RFC1996"/>, Sec for one or more [secondary] servers." (Quoted from <xref target="RFC1996" sectio
tion 2.1) Or, more nFormat="comma" section="2.1"/>) Or, more
specifically, <xref target="RFC2136"/> calls it "an authoritative server configu specifically, <xref target="RFC2136" format="default"/> calls it "an authoritati
red to be the source of AXFR or IXFR data ve server configured to be the source of AXFR or IXFR data
for one or more [secondary] servers". for one or more [secondary] servers".
Primary servers are also discussed in <xref target="RFC1034"/>. Primary servers are also discussed in <xref target="RFC1034" format="default"/>.
Although early DNS RFCs such as <xref target="RFC1996"/> referred to this as a " Although early DNS RFCs such as <xref target="RFC1996" format="default"/> referr
master", the current ed to this as a "master", the current
common usage has shifted to "primary".</t> common usage has shifted to "primary".</dd>
<dt>Primary master:</dt>
<t hangText='Primary master:'> <dd>
<iref item='Primary master'/> <iref item="Primary master" subitem="" primary="false"/>
"The primary master is named in the zone's SOA MNAME field and "The primary master is named in the zone's SOA MNAME field and
optionally by an NS RR." (Quoted from <xref target="RFC1996"/>, Section 2.1) optionally by an NS RR." (Quoted from <xref target="RFC1996" sectionFormat="comm
<xref target="RFC2136"/> defines "primary master" as a" section="2.1"/>)
<xref target="RFC2136" format="default"/> defines "primary master" as
"Master server at the root of the AXFR/IXFR dependency graph. "Master server at the root of the AXFR/IXFR dependency graph.
The primary master is named in the zone's SOA MNAME field and optionally by an N S RR. There is by The primary master is named in the zone's SOA MNAME field and optionally by an N S RR. There is by
definition only one primary master server per zone." definition only one primary master server per zone."
</t> </dd>
<dt/>
<t>The idea of a primary master is only used in <xref target="RFC1996"/> and <xr <dd>The idea of a primary master is only used in <xref target="RFC1996"
ef target="RFC2136"/>. format="default"/> and <xref target="RFC2136" format="default"/>.
A modern interpretation of the term "primary master" is a server that is both au thoritative for a zone A modern interpretation of the term "primary master" is a server that is both au thoritative for a zone
and that gets its updates to the zone from configuration (such as a master file) and that gets its updates to the zone from configuration (such as a master file)
or from UPDATE transactions.</t> or from UPDATE transactions.</dd>
<dt>Stealth server:</dt>
<t hangText='Stealth server:'> <dd>
<iref item='Stealth server'/> <iref item="Stealth server" subitem="" primary="false"/>
This is "like a slave server except not listed in an NS RR for This is "like a slave server except not listed in an NS RR for
the zone." (Quoted from <xref target="RFC1996"/>, Section 2.1)</t> the zone." (Quoted from <xref target="RFC1996" sectionFormat="comma" section="2.
1"/>)</dd>
<t hangText='Hidden master:'> <dt>Hidden master:</dt>
<iref item='Hidden master'/> <dd>
<iref item="Hidden master" subitem="" primary="false"/>
A stealth server that is a primary server for zone transfers. "In this arrangeme nt, the A stealth server that is a primary server for zone transfers. "In this arrangeme nt, the
master name server that processes the updates is unavailable to general hosts on the master name server that processes the updates is unavailable to general hosts on the
Internet; it is not listed in the NS RRset." (Quoted from Internet; it is not listed in the NS RRset." (Quoted from
<xref target="RFC6781"/>, Section 3.4.3) An earlier RFC, <xref target="RFC4641" <xref target="RFC6781" sectionFormat="comma" section="3.4.3"/>)
/>, said <xref target="RFC4641" format="default"/> said
that the hidden master's name "appears in the SOA RRs MNAME field", although, in that the hidden master's name "appears in the SOA RRs MNAME field"; however, the
some name does not appear at all in the global DNS in some setups. A hidden master
setups, the name does not appear at all in the global DNS. A hidden master can can also be a
also be a secondary server for the zone itself.</dd>
secondary server for the zone itself.</t> <dt>Forwarding:</dt>
<dd>
<t hangText='Forwarding:'> <iref item="Forwarding" subitem="" primary="false"/>
<iref item='Forwarding'/>
The process of one server sending a DNS query with the The process of one server sending a DNS query with the
RD bit set to 1 to another server to resolve that query. Forwarding is RD bit set to 1 to another server to resolve that query. Forwarding is
a function of a DNS resolver; it is different than simply blindly a function of a DNS resolver; it is different than simply blindly
relaying queries.</t> relaying queries.</dd>
<t><xref target="RFC5625"/> does not give a specific definition for forwarding, <dt/>
but <dd>
<xref target="RFC5625" format="default"/> does not give a specific def
inition for forwarding, but
describes in detail what features a system that forwards needs to describes in detail what features a system that forwards needs to
support. Systems that forward are sometimes called "DNS proxies", but support. Systems that forward are sometimes called "DNS proxies", but
that term has not yet been defined (even in <xref target="RFC5625"/>).</t> that term has not yet been defined (even in <xref target="RFC5625" format="defau
lt"/>).</dd>
<t hangText='Forwarder:'> <dt>Forwarder:</dt>
<iref item='Forwarder'/> <dd>
Section 1 of <xref target="RFC2308"/> describes a forwarder as "a <iref item="Forwarder" subitem="" primary="false"/>
<xref target="RFC2308" sectionFormat="of" section="1"/> describes a forwarder as
"a
nameserver used to resolve queries instead of directly using the nameserver used to resolve queries instead of directly using the
authoritative nameserver chain". <xref target="RFC2308"/> further says "The authoritative nameserver chain". <xref target="RFC2308" format="default"/> furt her says "The
forwarder typically either has better access to the internet, or forwarder typically either has better access to the internet, or
maintains a bigger cache which may be shared amongst many resolvers." maintains a bigger cache which may be shared amongst many resolvers."
That definition appears to suggest that forwarders That definition appears to suggest that forwarders
normally only query authoritative servers. In current use, however, normally only query authoritative servers. In current use, however,
forwarders often stand between stub resolvers and recursive servers. forwarders often stand between stub resolvers and recursive servers.
<xref target="RFC2308"/> is silent on whether a forwarder is iterative-only or <xref target="RFC2308" format="default"/> is silent on whether a forwarder is it
can be a full-service resolver.</t> erative-only or
can be a full-service resolver.</dd>
<t hangText='Policy-implementing resolver:'> <dt>Policy-implementing resolver:</dt>
<iref item='Policy-implementing resolver'/> <dd>
<iref item="Policy-implementing resolver" subitem="" primary="false"/>
A resolver acting in recursive mode that changes some of the answers A resolver acting in recursive mode that changes some of the answers
that it returns based on policy criteria, such as to prevent access to that it returns based on policy criteria, such as to prevent access to
malware sites or objectionable content. In general, a stub resolver has no idea malware sites or objectionable content. In general, a stub resolver has no idea
whether upstream resolvers implement such policy or, if they do, the exact whether upstream resolvers implement such policy or, if they do, the exact
policy about what changes will be made. policy about what changes will be made.
In some cases, the user of the stub resolver has selected the policy-implementin g resolver In some cases, the user of the stub resolver has selected the policy-implementin g resolver
with the explicit intention of using it to implement the policies. In other cas es, with the explicit intention of using it to implement the policies. In other cas es,
policies are imposed without the user of the stub resolver being informed.</t> policies are imposed without the user of the stub resolver being informed.</dd>
<dt>Open resolver:</dt>
<t hangText='Open resolver:'> <dd>
<iref item='Open resolver'/> <iref item="Open resolver" subitem="" primary="false"/>
A full-service resolver that accepts and processes queries from any (or nearly a ny) client. A full-service resolver that accepts and processes queries from any (or nearly a ny) client.
This is sometimes also called a "public resolver", although the term "public res olver" This is sometimes also called a "public resolver", although the term "public res olver"
is used more with open resolvers that are meant to be open, as compared to the v ast majority of open is used more with open resolvers that are meant to be open, as compared to the v ast majority of open
resolvers that are probably misconfigured to be open. resolvers that are probably misconfigured to be open.
Open resolvers are discussed in <xref target="RFC5358"/>.</t> Open resolvers are discussed in <xref target="RFC5358" format="default"/>.</dd>
<dt>Split DNS:</dt>
<t hangText='Split DNS:'> <dd>
<iref item='Split DNS'/> <iref item="Split DNS" subitem="" primary="false"/>
<iref item='Split-horizon DNS'/> <iref item="Split-horizon DNS" subitem="" primary="false"/>
The terms "split DNS" and "split-horizon DNS" have long been used in the DNS com munity without The terms "split DNS" and "split-horizon DNS" have long been used in the DNS com munity without
formal definition. In general, they refer to situations in which formal definition. In general, they refer to situations in which
DNS servers that are authoritative for a particular set of domains DNS servers that are authoritative for a particular set of domains
provide partly or completely different answers in those domains depending provide partly or completely different answers in those domains depending
on the source of the query. The effect of this is that a domain name that on the source of the query.
is notionally globally unique nevertheless has different meanings for Nevertheless, the effect of this is that a domain name that
is notionally globally unique has different meanings for
different network users. This can sometimes be the result of a "view" different network users. This can sometimes be the result of a "view"
configuration, described below.</t> configuration, as described below.</dd>
<dt/>
<t>Section 3.8 of <xref target="RFC2775"/> gives a related definition that is to <dd><xref target="RFC2775" sectionFormat="of" section="3.8"/> gives a re
o specific to be generally useful.</t> lated definition that is too specific to be generally useful.</dd>
<dt>View:</dt>
<t hangText='View:'> <dd>
<iref item='View'/> <iref item="View" subitem="" primary="false"/>
A configuration for a DNS server that allows it to provide A configuration for a DNS server that allows it to provide
different responses depending on attributes of the query, such as for "split DNS ". Typically, views differ different responses depending on attributes of the query, such as for "split DNS ". Typically, views differ
by the source IP address of a query, but can also be based on the destination IP address, by the source IP address of a query, but can also be based on the destination IP address,
the type of query (such as AXFR), whether it is recursive, and so on. the type of query (such as AXFR), whether it is recursive, and so on.
Views are often used to Views are often used to
provide more names or different addresses to queries from "inside" a protected n etwork provide more names or different addresses to queries from "inside" a protected n etwork
than to those "outside" that network. Views are not a standardized than to those "outside" that network. Views are not a standardized
part of the DNS, but they are widely implemented in server software.</t> part of the DNS, but they are widely implemented in server software.</dd>
<dt>Passive DNS:</dt>
<t hangText='Passive DNS:'> <dd>
<iref item='Passive DNS'/> <iref item="Passive DNS" subitem="" primary="false"/>
A mechanism to collect DNS data by storing DNS responses from name servers. Some of these systems A mechanism to collect DNS data by storing DNS responses from name servers. Some of these systems
also collect the DNS queries associated with the responses, although doing so ra ises some privacy also collect the DNS queries associated with the responses, although doing so ra ises some privacy
concerns. Passive DNS databases can be used to answer historical questions about DNS zones such as concerns. Passive DNS databases can be used to answer historical questions about DNS zones, such as
which values were present at a given time in the past, or when a name was spotte d first. which values were present at a given time in the past, or when a name was spotte d first.
Passive DNS databases allow searching of the stored records on keys other than Passive DNS databases allow searching of the stored records on keys other than
just the name and type, such as "find all names which have A records of a just the name and type, such as "find all names which have A records of a
particular value".</t> particular value".</dd>
<dt>Anycast:</dt>
<t hangText='Anycast:'> <dd>
<iref item='Anycast'/> <iref item="Anycast" subitem="" primary="false"/>
"The practice of making a particular service address available in multiple, disc rete, autonomous "The practice of making a particular service address available in multiple, disc rete, autonomous
locations, such that datagrams sent are routed to one of several available locat ions." locations, such that datagrams sent are routed to one of several available locat ions."
(Quoted from <xref target="RFC4786"/>, Section 2) (Quoted from <xref target="RFC4786" sectionFormat="comma" section="2"/>)
See <xref target="RFC4786"/> for more detail on Anycast and other terms that are See <xref target="RFC4786" format="default"/> for more detail on Anycast and oth
specific to its use.</t> er terms that are
specific to its use.</dd>
<t hangText='Instance:'> <dt>Instance:</dt>
<iref item='Instance'/> <dd>
<iref item="Instance" subitem="" primary="false"/>
"When anycast routing is used to allow more than one server to have the same IP "When anycast routing is used to allow more than one server to have the same IP
address, each one of those servers is commonly referred to as an 'instance'." address, each one of those servers is commonly referred to as an 'instance'."
It goes on to say: "An instance of a server, such as a root server, is often ref erred to as an 'Anycast It goes on to say: "An instance of a server, such as a root server, is often ref erred to as an 'Anycast
instance'." (Quoted from <xref target="RSSAC026" />)</t> instance'." (Quoted from <xref target="RSSAC026" format="default"/>)</dd>
<dt>Privacy-enabling DNS server:</dt>
<t hangText='Privacy-enabling DNS server:'> <dd>
<iref item='Privacy-enabling DNS server'/> <iref item="Privacy-enabling DNS server" subitem="" primary="false"/>
"A DNS server that implements "A DNS server that implements
DNS over TLS <xref target="RFC7858"/> and may optionally implement DNS over DTLS DNS over TLS <xref target="RFC7858" format="default"/> and may optionally implem
<xref target="RFC8094"/>." (Quoted from <xref target="RFC8310"/>, Section 2) ent DNS over DTLS
<xref target="RFC8094" format="default"/>." (Quoted from <xref target="RFC8310"
sectionFormat="comma" section="2"/>)
Other types of DNS servers might also be considered privacy-enabling, such as th ose Other types of DNS servers might also be considered privacy-enabling, such as th ose
running DNS-over-HTTPS <xref target="RFC8484" /> or DNS-over-QUIC <xref target=" running DNS-over-HTTPS <xref target="RFC8484" format="default"/> or DNS-over-QUI
RFC9250" />.</t> C <xref target="RFC9250" format="default"/>.</dd>
<dt>DNS-over-TLS (DoT):</dt>
<t hangText='DNS-over-TLS (DoT):'> <dd>
<iref item='DNS-over-TLS'/> <iref item="DNS-over-TLS" subitem="" primary="false"/>
<iref item='DoT'/> <iref item="DoT" subitem="" primary="false"/>
DNS over TLS as defined in <xref target="RFC7858"/> and its successors.</t> DNS over TLS as defined in <xref target="RFC7858" format="default"/> and its suc
cessors.</dd>
<t hangText='DNS-over-HTTPS (DoH):'> <dt>DNS-over-HTTPS (DoH):</dt>
<iref item='DNS-over-HTTPS'/> <dd>
<iref item='DoH'/> <iref item="DNS-over-HTTPS" subitem="" primary="false"/>
DNS over HTTPS as defined in <xref target="RFC8484" /> and its successors.</t> <iref item="DoH" subitem="" primary="false"/>
DNS over HTTPS as defined in <xref target="RFC8484" format="default"/> and its s
<t hangText='DNS-over-QUIC (DoQ):'> uccessors.</dd>
<iref item='DNS-over-QUIC'/> <dt>DNS-over-QUIC (DoQ):</dt>
<iref item='DoQ'/> <dd>
DNS over QUIC as defined in <xref target="RFC9250" /> and its successors. <iref item="DNS-over-QUIC" subitem="" primary="false"/>
<xref target="RFC9250" /> specifically defines DoQ as a general purpose transpor <iref item="DoQ" subitem="" primary="false"/>
t DNS over QUIC as defined in <xref target="RFC9250" format="default"/> and its su
for DNS that can be used in stub to recursive, recursive to authoritative or ccessors.
zone transfer scenarios.</t> <xref target="RFC9250" format="default"/> specifically defines DoQ as general-pu
rpose transport
<t hangText='Classic DNS:'> for DNS that can be used in stub to recursive, recursive to authoritative, and
<iref item='Classic DNS'/> zone transfer scenarios.</dd>
DNS over UDP or TCP as defined in <xref target="RFC1035" /> and its successors. <dt>Classic DNS:</dt>
<dd>
<iref item="Classic DNS" subitem="" primary="false"/>
DNS over UDP or DNS over TCP as defined in <xref target="RFC1035" format="defaul
t"/> and its successors.
Classic DNS applies to DNS communication between stub resolvers and recursive Classic DNS applies to DNS communication between stub resolvers and recursive
resolvers, and between recursive resolvers and authoritative servers. resolvers, and between recursive resolvers and authoritative servers.
This has sometimes been called "Do53". This has sometimes been called "Do53".
Classic DNS is not encrypted.</t> Classic DNS is not encrypted.</dd>
<dt>Recursive DoT (RDoT):</dt>
<t hangText='Recursive DoT (RDoT):'> <dd>
<iref item='Recursive DoT'/> <iref item="Recursive DoT" subitem="" primary="false"/>
<iref item='RDoT'/> <iref item="RDoT" subitem="" primary="false"/>
RDoT specifically means DNS-over-TLS for transport between a stub resolver and a RDoT specifically means DNS-over-TLS for transport between a stub resolver and a
recursive resolver, or between a recursive resolver and another recursive resolv er. recursive resolver, or between a recursive resolver and another recursive resolv er.
This term is necessary because it is expected that DNS-over-TLS will later be This term is necessary because it is expected that DNS-over-TLS will later be
defined as a transport between recursive resolvers and authoritative servers.</t defined as a transport between recursive resolvers and authoritative servers.</d
> d>
<dt>Authoritative DoT (ADoT):</dt>
<t hangText='Authoritative DoT (ADoT):'> <dd>
<iref item='ADoT'/> <iref item="ADoT" subitem="" primary="false"/>
If DNS-over-TLS is later defined as a transport between recursive resolvers and If DNS-over-TLS is later defined as a transport between recursive resolvers and
authoritative servers, ADoT specifically means DNS-over-TLS for transport authoritative servers, ADoT specifically means DNS-over-TLS for transport
between recursive resolvers and authoritative servers.</t> between recursive resolvers and authoritative servers.</dd>
<dt>XFR-over-TLS (XoT):</dt>
<t hangText='XFR-over-TLS (XoT):'> <dd>
<iref item='XoT'/> <iref item="XoT" subitem="" primary="false"/>
<iref item='AXoT'/> <iref item="AXoT" subitem="" primary="false"/>
<iref item='IXoT'/> <iref item="IXoT" subitem="" primary="false"/>
DNS zone transfer over TLS, as specified in <xref target="RFC9103"/>. DNS zone transfer over TLS, as specified in <xref target="RFC9103" format="defau
This term applies to both AXFR over TLS (AXoT) and IXFR over TLS (IXoT).</t> lt"/>.
This term applies to both AXFR over TLS (AXoT) and IXFR over TLS (IXoT).</dd>
</list></t> </dl>
</section> </section>
<section anchor="zones" numbered="true" toc="default">
<section anchor="zones" title="Zones"> <name>Zones</name>
<t>This section defines terms that are used when discussing zones that are
<t>This section defines terms that are used when discussing zones that are being being served or retrieved.</t>
served or retrieved.</t> <dl newline="false" spacing="normal">
<dt>Zone:</dt>
<t><list style="hanging"> <dd>
<iref item="Zone" subitem="" primary="false"/>
<t hangText='Zone:'>
<iref item='Zone'/>
"Authoritative information is "Authoritative information is
organized into units called ZONEs, and these zones can be organized into units called ZONEs, and these zones can be
automatically distributed to the name servers which provide automatically distributed to the name servers which provide
redundant service for the data in a zone." (Quoted from <xref target="RFC1034"/ redundant service for the data in a zone." (Quoted from <xref target="RFC1034"
>, Section 2.4)</t> sectionFormat="comma" section="2.4"/>)</dd>
<dt>Child:</dt>
<t hangText='Child:'> <dd>
<iref item='Child'/> <iref item="Child" subitem="" primary="false"/>
"The entity on record that has the delegation of the domain from the "The entity on record that has the delegation of the domain from the
Parent." (Quoted from <xref target="RFC7344"/>, Section 1.1)</t> Parent." (Quoted from <xref target="RFC7344" sectionFormat="comma" section="1.1"
/>)</dd>
<t hangText='Parent:'> <dt>Parent:</dt>
<iref item='Parent'/> <dd>
"The domain in which the Child is registered." (Quoted from <xref target="RFC73 <iref item="Parent" subitem="" primary="false"/>
44"/>, Section 1.1) Earlier, "The domain in which the Child is registered." (Quoted from <xref target="RFC73
"parent name server" was defined in <xref target="RFC0882"/> as "the name server 44" sectionFormat="comma" section="1.1"/>) Earlier,
that has authority over the place "parent name server" was defined in <xref target="RFC0882" format="default"/> as
"the name server that has authority over the place
in the domain name space that will hold the new domain". (Note in the domain name space that will hold the new domain". (Note
that <xref target="RFC0882"/> was obsoleted by <xref target="RFC1034"/> and <xre that <xref target="RFC0882" format="default"/> was obsoleted by <xref target="RF
f target="RFC1035"/>.) <xref target="RFC0819"/> also has some description of C1034" format="default"/> and <xref target="RFC1035" format="default"/>.)
the relationship between parents and children.</t>
<t hangText='Origin:'> <xref target="RFC0819" format="default"/> also has some description of
<iref item='Origin'/> the relationship between parents and children.</dd>
</t> <dt>Origin:</dt>
<t>There are two different uses for this term:<list style="format (%c)"> <dd>
<t>"The domain name that <iref item="Origin" subitem="" primary="false"/>
</dd>
<dt/>
<dd>
<t>There are two different uses for this term:</t>
<ol spacing="normal" type="(%c)"><li>"The domain name that
appears at the top of a zone (just below the cut that separates the appears at the top of a zone (just below the cut that separates the
zone from its parent)... The name of the zone is the same as the name zone from its parent)... The name of the zone is the same as the name
of the domain at the zone's origin." (Quoted from <xref target="RFC2181"/>, Sec tion 6) These days, this sense of of the domain at the zone's origin." (Quoted from <xref target="RFC2181" sectio nFormat="comma" section="6"/>) These days, this sense of
"origin" and "apex" (defined below) are often used "origin" and "apex" (defined below) are often used
interchangeably.</t> interchangeably.</li>
<t>The domain name within which a given relative domain name <li>The domain name within which a given relative domain name
appears in zone files. Generally seen in the context of "$ORIGIN", which is a appears in zone files. Generally seen in the context of "$ORIGIN", which is a
control entry defined in <xref target="RFC1035"/>, Section 5.1, as part of the m aster control entry defined in <xref target="RFC1035" sectionFormat="comma" section="5 .1"/>, as part of the master
file format. For example, if the $ORIGIN is set to "example.org.", file format. For example, if the $ORIGIN is set to "example.org.",
then a master file line for "www" is in fact an entry for then a master file line for "www" is in fact an entry for
"www.example.org.".</t></list></t> "www.example.org.".</li>
</ol>
<t hangText='Apex:'> </dd>
<iref item='Apex'/> <dt>Apex:</dt>
<dd>
<iref item="Apex" subitem="" primary="false"/>
The point in the tree at an owner of an SOA and corresponding authoritative NS R Rset. The point in the tree at an owner of an SOA and corresponding authoritative NS R Rset.
This is also called the "zone apex". This is also called the "zone apex".
<xref target="RFC4033"/> defines it as "the name at the child's side of a zone c ut". <xref target="RFC4033" format="default"/> defines it as "the name at the child's side of a zone cut".
The "apex" can usefully be thought of as a data-theoretic description of a tree structure, The "apex" can usefully be thought of as a data-theoretic description of a tree structure,
and "origin" is the name of the same concept when it is implemented in and "origin" is the name of the same concept when it is implemented in
zone files. The distinction is not always maintained in use, however, zone files. The distinction is not always maintained in use, however,
and one can find uses that conflict subtly with this definition. and one can find uses that conflict subtly with this definition.
<xref target="RFC1034"/> uses the term "top node of the zone" as a synonym of "a <xref target="RFC1034" format="default"/> uses the term "top node of the zone" a
pex", but that term is not widely used. s a synonym of "apex", but that term is not widely used.
These days, the first sense of "origin" (above) and "apex" are often used interc These days, the first sense of "origin" (above) and "apex" are often used interc
hangeably.</t> hangeably.</dd>
<dt>Zone cut:</dt>
<t hangText='Zone cut:'> <dd>
<iref item='Zone cut'/> <iref item="Zone cut" subitem="" primary="false"/>
The delimitation point between two zones where the origin The delimitation point between two zones where the origin
of one of the zones is the child of the other zone.</t> of one of the zones is the child of the other zone.</dd>
<t>"Zones are delimited by 'zone cuts'. Each zone cut separates a <dt/>
'child' zone (below the cut) from a 'parent' zone (above the cut)." (Quoted fro <dd>"Zones are delimited by 'zone cuts'. Each zone cut separates a
m <xref target="RFC2181"/>, Section 6; note that this is barely an ostensive 'child' zone (below the cut) from a 'parent' zone (above the cut)." (Quoted fro
m <xref target="RFC2181" sectionFormat="comma" section="6"/>; note that this is
barely an ostensive
definition.) definition.)
Section 4.2 of <xref target="RFC1034"/> uses "cuts" instead of "zone cut".</t> <xref target="RFC1034" sectionFormat="of" section="4.2"/> uses "cuts" instead of
"zone cut".</dd>
<t hangText='Delegation:'> <dt>Delegation:</dt>
<iref item='Delegation'/> <dd>
<iref item="Delegation" subitem="" primary="false"/>
The process by which a separate zone is created in the The process by which a separate zone is created in the
name space beneath the apex of a given domain. Delegation happens when an NS name space beneath the apex of a given domain. Delegation happens when an NS
RRset is added in the parent zone for the child origin. Delegation RRset is added in the parent zone for the child origin. Delegation
inherently happens at a zone cut. inherently happens at a zone cut.
The term is also commonly a noun: the new zone that is created by the act of del The term is also commonly a noun: the new zone that is created by the act of del
egating.</t> egating.</dd>
<dt>Authoritative data:</dt>
<t hangText='Authoritative data:'> <dd>
<iref item='Authoritative data'/> <iref item="Authoritative data" subitem="" primary="false"/>
"All of the RRs attached to all of the nodes from the top node of the zone "All of the RRs attached to all of the nodes from the top node of the zone
down to leaf nodes or nodes above cuts around the bottom edge of the zone." (Quo ted from down to leaf nodes or nodes above cuts around the bottom edge of the zone." (Quo ted from
<xref target="RFC1034"/>, Section 4.2.1) <xref target="RFC1034" sectionFormat="comma" section="4.2.1"/>)
Note that this definition might inadvertently also cause any NS records Note that this definition might inadvertently also cause any NS records
that appear in the zone to be included, even those that might not truly be autho ritative because there are that appear in the zone to be included, even those that might not truly be autho ritative, because there are
identical NS RRs below the zone cut. This reveals the ambiguity in identical NS RRs below the zone cut. This reveals the ambiguity in
the notion of authoritative data, because the parent-side NS records the notion of authoritative data, because the parent-side NS records
authoritatively indicate the delegation, even though they are not authoritatively indicate the delegation, even though they are not
themselves authoritative data.</t> themselves authoritative data.</dd>
<dt/>
<t><xref target="RFC4033"/>, Section 2, defines "Authoritative RRset", which is <dd>
related <xref target="RFC4033" sectionFormat="comma" section="2"/>, defines "A
to authoritative data but has a more precise definition.</t> uthoritative RRset", which is related
to authoritative data but has a more precise definition.</dd>
<t hangText='Lame delegation:'> <dt>Lame delegation:</dt>
<iref item='Lame delegation'/> <dd>
<iref item="Lame delegation" subitem="" primary="false"/>
<!--Begin DNE -->
"A lame delegations exists [sic] when a nameserver is delegated responsibility f or providing nameservice "A lame delegations exists [sic] when a nameserver is delegated responsibility f or providing nameservice
for a zone (via NS records) but is not performing nameservice for that zone (usu ally because it is for a zone (via NS records) but is not performing nameservice for that zone (usu ally because it is
not set up as a primary or secondary for the zone)." (Quoted from <xref target=" not set up as a primary or secondary for the zone)." (Quoted from <xref target="
RFC1912"/>, Section 2.8) RFC1912" sectionFormat="comma" section="2.8"/>)
<!--End DNE -->
Another definition is that a lame delegation Another definition is that a lame delegation
<!--Begin DNE -->
"...happens when a name server is listed in the NS records for some domain and in fact it is not a "...happens when a name server is listed in the NS records for some domain and in fact it is not a
server for that domain. Queries are thus sent to the wrong servers, who don't kn ow nothing [sic] (at least server for that domain. Queries are thus sent to the wrong servers, who don't kn ow nothing [sic] (at least
not as expected) about the queried domain. Furthermore, sometimes these hosts (i f they exist!) don't not as expected) about the queried domain. Furthermore, sometimes these hosts (i f they exist!) don't
even run name servers." (Quoted from <xref target="RFC1713"/>, Section 2.3)</t> even run name servers." (Quoted from <xref target="RFC1713" sectionFormat="comm
<!--End DNE --> a" section="2.3"/>)</dd>
<t>These early definitions do not match the current use of the term "lame delega <dt/>
tion", <dd>
but there is not consensus on what a lame delegation is. <t>These early definitions do not match the current use of the term "l
ame delegation",
but there is no consensus on what a lame delegation is.
The term is used not only for the specific case described above, The term is used not only for the specific case described above,
but for a variety of other flaws in delegations that lead to non-authoritative but for a variety of other flaws in delegations that lead to non-authoritative
answers or no answers at all, such as: answers or no answers at all, such as:
<list style="symbols">
<t>
a nameserver with an NS record for a zone that does not answer DNS queries
</t>
<t>
a nameserver with an IP address that is not reachable by the resolver
</t> </t>
<t> <ul spacing="normal">
<li>
a nameserver with an NS record for a zone that does not answer DNS queries;
</li>
<li>
a nameserver with an IP address that is not reachable by the resolver; and
</li>
<li>
a nameserver that responds to a query for a specific name with an error or a nameserver that responds to a query for a specific name with an error or
without the authoritative bit set without the authoritative bit set.
</t> </li>
</list></t> </ul>
</dd>
<t>Because the term in current usage has drifted from the original definition, a <dt/>
nd now <dd>Because the term in current usage has drifted from the original defi
is not specific or clear as to the intended meaning, it should be considered his nition, and now
toric, is not specific or clear as to the intended meaning, it should be considered his
and avoided in favor of terms that are specific and clear.</t> toric
and avoided in favor of terms that are specific and clear.</dd>
<t hangText='Glue records:'> <dt>Glue records:</dt>
<iref item='Glue records'/> <dd>
<iref item="Glue records" subitem="" primary="false"/>
<!--begin DNE -->
"...[Resource records] which are not part of the authoritative data [of the zone ], "...[Resource records] which are not part of the authoritative data [of the zone ],
and are address RRs for the [name] servers [in subzones]. These RRs are only and are address RRs for the [name] servers [in subzones]. These RRs are only
necessary if the name server's name is 'below' the cut, and are only used as par t of a necessary if the name server's name is 'below' the cut, and are only used as par t of a
referral response." Without glue "we could be faced with the situation where the NS RRs referral response." Without glue "we could be faced with the situation where the NS RRs
tell us that in order to learn a name server's address, we should contact the se rver using tell us that in order to learn a name server's address, we should contact the se rver using
the address we wish to learn." (Quoted from <xref target="RFC1034"/>, Section 4 the address we wish to learn." (Quoted from <xref target="RFC1034" sectionForma
.2.1)</t> t="comma" section="4.2.1"/>)</dd>
<!--End DNE -->
<t>A later definition is that glue <dt/>
<!--Begin DNE --> <dd>A later definition is that glue
"includes any record in a zone file that is not properly "includes any record in a zone file that is not properly
part of that zone, including nameserver records of delegated sub-zones (NS recor ds), part of that zone, including nameserver records of delegated sub-zones (NS recor ds),
address records that accompany those NS records (A, AAAA, etc), and any other st ray data address records that accompany those NS records (A, AAAA, etc), and any other st ray data
that might appear." (Quoted from <xref target="RFC2181"/>, Section 5.4.1) that might appear." (Quoted from <xref target="RFC2181" sectionFormat="comma" s
<!--End DNE --> ection="5.4.1"/>)
Although glue is sometimes used today Although glue is sometimes used today
with this wider definition in mind, the context surrounding the definition in <x ref target="RFC2181"/> with this wider definition in mind, the context surrounding the definition in <x ref target="RFC2181" format="default"/>
suggests it is intended to apply to the use of glue within the document itself a nd not suggests it is intended to apply to the use of glue within the document itself a nd not
necessarily beyond.</t> necessarily beyond.</dd>
<dt/>
<t>In an NS record, there are three types of relationships between the owner nam <dd>In an NS record, there are three types of relationships between the
e of the record owner name of the record, the name in the NS RDATA, and the zone origin: unrelat
and the name in the NS RDATA and the zone origin: unrelated, in-domain, and sibl ed, in-domain, and sibling domain.
ing domain.
The application of these three types of relationships to glue records is defined in The application of these three types of relationships to glue records is defined in
<xref target="I-D.ietf-dnsop-glue-is-not-optional"/>. <xref target="RFC9471" format="default"/>.
</t> </dd>
<dt/>
<t>An unrelated relationship is one where the NS RDATA contains a name server <dd>An unrelated relationship is one where the NS RDATA contains a name
server
that is not subordinate to the zone origin and therefore is not part of the same zone. that is not subordinate to the zone origin and therefore is not part of the same zone.
</t> </dd>
<dt/>
<t> <dd>
<iref item='In-domain'/> <iref item="In-domain" subitem="" primary="false"/>
An in-domain relationship is one where the NS RDATA contains a name server An in-domain relationship is one where the NS RDATA contains a name server
whose name is either whose name is either
subordinate to or (rarely) the same as the owner name of the NS resource records . subordinate to or (rarely) the same as the owner name of the NS resource records .
For example, a delegation for "child.example.com" might have an in-domain name For example, a delegation for "child.example.com" might have an in-domain name
server called "ns.child.example.com". server called "ns.child.example.com".
</t> </dd>
<dt/>
<t> <dd>
<iref item='Sibling domain'/> <iref item="Sibling domain" subitem="" primary="false"/>
A sibling domain relationship is one where the NS RDATA contains a name server A sibling domain relationship is one where the NS RDATA contains a name server
whose name is either subordinate to or whose name is either subordinate to or
(rarely) the same as the zone origin of the parent and not subordinate to or the same as the (rarely) the same as the zone origin of the parent and not subordinate to or the same as the
owner name of the NS resource records. owner name of the NS resource records.
For example, a delegation for "child.example.com" in "example.com" zone might ha ve For example, a delegation for "child.example.com" in "example.com" zone might ha ve
a sibling domain name server called "ns.another.example.com". a sibling domain name server called "ns.another.example.com".
</t> </dd>
<dt/>
<t>The following table shows examples of delegation types:</t> <dd>The following table shows examples of delegation types:</dd>
<dt/><dd>
<t><table anchor="delegation_types"> <table anchor="delegation_types">
<thead> <thead>
<tr> <th>Delegation</th> <th>Parent</th> <th>Name Server Name</th> <th>T <tr>
ype</th></tr> <th>Delegation</th>
</thead> <th>Parent</th>
<tbody> <th>Name Server Name</th>
<tr> <td>com</td> <td>.</td> <td>a.gtld-servers.net</td> <td>sibling dom <th>Type</th>
ain</td></tr> </tr>
<tr> <td>net</td> <td>.</td> <td>a.gtld-servers.net</td> <td>in-domain</ </thead>
td></tr> <tbody>
<tr> <td>example.org</td> <td>org</td> <td>ns.example.org</td> <td>in-do <tr>
main</td></tr> <td>com</td>
<tr> <td>example.org</td> <td>org</td> <td>ns.ietf.org</td> <td>sibling <td>.</td>
domain</td></tr> <td>a.gtld-servers.net</td>
<tr> <td>example.org</td> <td>org</td> <td>ns.example.com</td> <td>unrel <td>sibling domain</td>
ated</td></tr> </tr>
<tr> <td>example.jp</td> <td>jp</td> <td>ns.example.jp</td> <td>in-domai <tr>
n</td></tr> <td>net</td>
<tr> <td>example.jp</td> <td>jp</td> <td>ns.example.ne.jp</td> <td>sibli <td>.</td>
ng domain</td></tr> <td>a.gtld-servers.net</td>
<tr> <td>example.jp</td> <td>jp</td> <td>ns.example.com</td> <td>unrelat <td>in-domain</td>
ed</td></tr> </tr>
</tbody> <tr>
</table></t> <td>example.org</td>
<td>org</td>
<t hangText='Bailiwick:'> <td>ns.example.org</td>
<iref item='Bailiwick'/> <td>in-domain</td>
<iref item='In-bailiwick'/> </tr>
<iref item='Out-of-bailiwick'/> <tr>
<td>example.org</td>
<td>org</td>
<td>ns.ietf.org</td>
<td>sibling domain</td>
</tr>
<tr>
<td>example.org</td>
<td>org</td>
<td>ns.example.com</td>
<td>unrelated</td>
</tr>
<tr>
<td>example.jp</td>
<td>jp</td>
<td>ns.example.jp</td>
<td>in-domain</td>
</tr>
<tr>
<td>example.jp</td>
<td>jp</td>
<td>ns.example.ne.jp</td>
<td>sibling domain</td>
</tr>
<tr>
<td>example.jp</td>
<td>jp</td>
<td>ns.example.com</td>
<td>unrelated</td>
</tr>
</tbody>
</table>
</dd>
<dt>Bailiwick:</dt>
<dd>
<iref item="Bailiwick" subitem="" primary="false"/>
<iref item="In-bailiwick" subitem="" primary="false"/>
<iref item="Out-of-bailiwick" subitem="" primary="false"/>
"In-bailiwick" and "Out-of-bailiwick" are modifiers used to describe the relatio nship between "In-bailiwick" and "Out-of-bailiwick" are modifiers used to describe the relatio nship between
a zone and the name servers for that zone. a zone and the name servers for that zone.
The dictionary definition of bailiwick has been observed to cause more co nfusion than meaning for this use. The dictionary definition of bailiwick has been observed to cause more co nfusion than meaning for this use.
These terms should be considered historic in nature.</t> These terms should be considered historic in nature.</dd>
<dt>Root zone:</dt>
<t hangText='Root zone:'> <dd>
<iref item='Root zone'/> <iref item="Root zone" subitem="" primary="false"/>
The zone of a DNS-based tree whose apex is the zero-length label. The zone of a DNS-based tree whose apex is the zero-length label.
Also sometimes called "the DNS root".</t> Also sometimes called "the DNS root".</dd>
<dt>Empty non-terminals (ENTs):</dt>
<t hangText='Empty non-terminals (ENT):'> <dd>
<iref item='Empty non-terminals (ENT)'/> <iref item="Empty non-terminals (ENTs)" subitem="" primary="false"/>
"Domain names that own no resource records but have subdomains that do." "Domain names that own no resource records but have subdomains that do."
(Quoted from <xref target="RFC4592"/>, Section 2.2.2) (Quoted from <xref target="RFC4592" sectionFormat="comma" section="2.2.2"/>)
A typical example is in SRV records: in the name A typical example is in SRV records: in the name
"_sip._tcp.example.com", it is likely that "_tcp.example.com" has no RRsets, but "_sip._tcp.example.com", it is likely that "_tcp.example.com" has no RRsets, but
that "_sip._tcp.example.com" has (at least) an SRV RRset.</t> that "_sip._tcp.example.com" has (at least) an SRV RRset.</dd>
<dt>Delegation-centric zone:</dt>
<t hangText='Delegation-centric zone:'> <dd>
<iref item='Delegation-centric zone'/> <iref item="Delegation-centric zone" subitem="" primary="false"/>
A zone that consists mostly of delegations to child zones. This term is A zone that consists mostly of delegations to child zones. This term is
used in contrast to a zone that might have some delegations to child zones but a lso has many data used in contrast to a zone that might have some delegations to child zones but a lso has many data
resource records for the zone itself and/or for child zones. resource records for the zone itself and/or for child zones.
The term is used in <xref target="RFC4956"/> and <xref target="RFC5155"/>, but i The term is used in <xref target="RFC4956" format="default"/> and <xref target="
t is not defined in either document.</t> RFC5155" format="default"/>, but it is not defined in either document.</dd>
<dt>Occluded name:</dt>
<t hangText='Occluded name:'> <dd>
<iref item='Occluded name'/> <iref item="Occluded name" subitem="" primary="false"/>
<!--begin DNE -->
"The addition of a delegation point via dynamic update will render all subordina te "The addition of a delegation point via dynamic update will render all subordina te
domain names to be in a limbo, still part of the zone but not available to the l ookup process. The domain names to be in a limbo, still part of the zone but not available to the l ookup process. The
addition of a DNAME resource record has the same impact. The subordinate names are said to be addition of a DNAME resource record has the same impact. The subordinate names are said to be
'occluded'." (Quoted from <xref target="RFC5936"/>, Section 3.5)</t> 'occluded'." (Quoted from <xref target="RFC5936" sectionFormat="comma" section=
"3.5"/>)</dd>
<t hangText='Fast flux DNS:'> <dt>Fast flux DNS:</dt>
<iref item='Fast flux DNS'/> <dd>
<iref item="Fast flux DNS" subitem="" primary="false"/>
This "occurs when a domain is [found] in DNS using A records to multiple IP addr esses, This "occurs when a domain is [found] in DNS using A records to multiple IP addr esses,
each of which has a very short Time-to-Live (TTL) value associated with it. Thi s means each of which has a very short Time-to-Live (TTL) value associated with it. Thi s means
that the domain resolves to varying IP addresses over a short period of time." that the domain resolves to varying IP addresses over a short period of time."
(Quoted from <xref target="RFC6561"/>, Section 1.1.5, with a typo corrected) (Quoted from <xref target="RFC6561" sectionFormat="comma" section="1.1.5"/>, wit
In addition to having legitimate uses, fast flux DNS can used to deliver malware h a typo corrected)
. In addition to having legitimate uses, fast flux DNS can be used to deliver malw
are.
Because the addresses change so rapidly, it is difficult to Because the addresses change so rapidly, it is difficult to
ascertain all the hosts. It should be noted that the technique also works ascertain all the hosts. It should be noted that the technique also works
with AAAA records, but such use is not frequently observed on the with AAAA records, but such use is not frequently observed on the
Internet as of this writing.</t> Internet as of this writing.</dd>
<dt>Reverse DNS, reverse lookup:</dt>
<t hangText='Reverse DNS, reverse lookup:'> <dd>
<iref item='Reverse DNS, reverse lookup'/> <iref item="Reverse DNS, reverse lookup" subitem="" primary="false"/>
"The process of mapping an address to a name is "The process of mapping an address to a name is
generally known as a 'reverse lookup', and the IN-ADDR.ARPA and generally known as a 'reverse lookup', and the IN-ADDR.ARPA and
IP6.ARPA zones are said to support the 'reverse DNS'." IP6.ARPA zones are said to support the 'reverse DNS'."
(Quoted from <xref target="RFC5855"/>, Section 1) (Quoted from <xref target="RFC5855" sectionFormat="comma" section="1"/>)
</t> </dd>
<dt>Forward lookup:</dt>
<t hangText='Forward lookup:'> <dd>
<iref item='Forward lookup'/> <iref item="Forward lookup" subitem="" primary="false"/>
"Hostname-to-address translation". (Quoted from "Hostname-to-address translation". (Quoted from
<xref target="RFC3493" />, Section 6) <xref target="RFC3493" sectionFormat="comma" section="6"/>)
</t>
<t hangText='arpa: Address and Routing Parameter Area Domain:'> </dd>
<iref item='arpa: Address and Routing Parameter Area Domain'/> <dt>arpa (Address and Routing Parameter Area Domain):</dt><dd>
<iref item="Address and Routing Parameter Area Domain (arpa)" subitem=
"" primary="false"/>
"The 'arpa' domain was originally established as part of the initial "The 'arpa' domain was originally established as part of the initial
deployment of the DNS, to provide a transition mechanism from the deployment of the DNS to provide a transition mechanism from the
Host Tables that were common in the ARPANET, as well as a home for Host Tables that were common in the ARPANET, as well as a home for
the IPv4 reverse mapping domain. During 2000, the abbreviation was the IPv4 reverse mapping domain. During 2000, the abbreviation was
redesignated to 'Address and Routing Parameter Area' in the hope of redesignated to 'Address and Routing Parameter Area' in the hope of
reducing confusion with the earlier network name." reducing confusion with the earlier network name."
(Quoted from <xref target="RFC3172"/>, Section 2) (Quoted from <xref target="RFC3172" sectionFormat="comma" section="2"/>)
.arpa is an "infrastructure domain", .arpa is an "infrastructure domain",
a domain whose "role is to a domain whose "role is to
support the operating infrastructure of the Internet". support the operating infrastructure of the Internet".
(Quoted from <xref target="RFC3172"/>, Section 2) (Quoted from <xref target="RFC3172" sectionFormat="comma" section="2"/>)
See <xref target="RFC3172"/> for more history of this name. See <xref target="RFC3172" format="default"/> for more history of this name.
</t> </dd>
<dt>Service name:</dt>
<t hangText='Service name:'> <dd>
<iref item='Service name'/> <iref item="Service name" subitem="" primary="false"/>
"Service names are the unique key in the Service Name and Transport "Service names are the unique key in the Service Name and Transport
Protocol Port Number registry. This unique symbolic name for a Protocol Port Number registry. This unique symbolic name for a
service may also be used for other purposes, such as in DNS SRV service may also be used for other purposes, such as in DNS SRV
records." (Quoted from <xref target="RFC6335"/>, Section 5) records." (Quoted from <xref target="RFC6335" sectionFormat="comma" section="5"/
</t> >)
</dd>
</list></t> </dl>
</section> </section>
<section anchor="wildcards" numbered="true" toc="default">
<section anchor="wildcards" title="Wildcards"> <name>Wildcards</name>
<t><list style="hanging"> <dl newline="false" spacing="normal">
<dt>Wildcard:</dt>
<t hangText='Wildcard:'> <dd>
<iref item='Wildcard'/> <iref item="Wildcard" subitem="" primary="false"/>
<xref target="RFC1034"/> defined "wildcard", but in a way that turned out to be <xref target="RFC1034" format="default"/> defined "wildcard", but in a
way that turned out to be
confusing to implementers. confusing to implementers.
For an extended discussion of wildcards, including clearer definitions, see <xre f target="RFC4592"/>. For an extended discussion of wildcards, including clearer definitions, see <xre f target="RFC4592" format="default"/>.
Special treatment is given to RRs with owner names starting with the label "*". "Such RRs Special treatment is given to RRs with owner names starting with the label "*". "Such RRs
are called 'wildcards'. Wildcard RRs can be thought of as instructions for synth esizing RRs." are called 'wildcards'. Wildcard RRs can be thought of as instructions for synth esizing RRs."
(Quoted from <xref target="RFC1034"/>, Section 4.3.3) (Quoted from <xref target="RFC1034" sectionFormat="comma" section="4.3.3"/>)
</t> </dd>
<dt>Asterisk label:</dt>
<t hangText='Asterisk label:'> <dd>
<iref item='Asterisk label'/> <iref item="Asterisk label" subitem="" primary="false"/>
"The first octet is the normal label type and length for a 1-octet-long "The first octet is the normal label type and length for a 1-octet-long
label, and the second octet is the ASCII representation [RFC20] label, and the second octet is the ASCII representation <xref target="RFC0020"/>
for the '*' character. for the '*' character.
A descriptive name of a label equaling that value is an 'asterisk A descriptive name of a label equaling that value is an 'asterisk
label'." (Quoted from <xref target="RFC4592"/>, Section 2.1.1)</t> label'." (Quoted from <xref target="RFC4592" sectionFormat="comma" section="2.1.
1"/>)</dd>
<t hangText='Wildcard domain name:'> <dt>Wildcard domain name:</dt>
<iref item='Wildcard domain name'/> <dd>
<iref item="Wildcard domain name" subitem="" primary="false"/>
"A 'wildcard domain name' is defined by having its initial (i.e., "A 'wildcard domain name' is defined by having its initial (i.e.,
leftmost or least significant) label, in binary format: 0000 0001 0010 1010 (bin ary) = 0x01 0x2a (hexadecimal)". leftmost or least significant) label, in binary format: 0000 0001 0010 1010 (bin ary) = 0x01 0x2a (hexadecimal)".
(Quoted from <xref target="RFC4592"/>, Section 2.1.1) The second octet in this (Quoted from <xref target="RFC4592" sectionFormat="comma" section="2.1.1"/>) Th
label is the ASCII representation for the "*" character.</t> e second octet in this label is the ASCII representation for the "*" character.<
/dd>
<t hangText='Closest encloser:'> <dt>Closest encloser:</dt>
<iref item='Closest encloser'/> <dd>
<iref item="Closest encloser" subitem="" primary="false"/>
"The longest existing ancestor of a name." "The longest existing ancestor of a name."
(Quoted from <xref target="RFC5155"/>, Section 1.3) (Quoted from <xref target="RFC5155" sectionFormat="comma" section="1.3"/>)
An earlier definition is "The node in the zone's tree of existing An earlier definition is "The node in the zone's tree of existing
domain names that has the most labels matching the query name domain names that has the most labels matching the query name
(consecutively, counting from the root label downward). Each match (consecutively, counting from the root label downward). Each match
is a 'label match' and the order of the labels is the same." is a 'label match' and the order of the labels is the same."
(Quoted from <xref target="RFC4592"/>, Section 3.3.1) (Quoted from <xref target="RFC4592" sectionFormat="comma" section="3.3.1"/>)
</t> </dd>
<dt>Closest provable encloser:</dt>
<t hangText='Closest provable encloser:'> <dd>
<iref item='Closest provable encloser'/> <iref item="Closest provable encloser" subitem="" primary="false"/>
"The longest ancestor of a name that can "The longest ancestor of a name that can
be proven to exist. Note that this is only different from the be proven to exist. Note that this is only different from the
closest encloser in an Opt-Out zone." closest encloser in an Opt-Out zone."
(Quoted from <xref target="RFC5155"/>, Section 1.3) (Quoted from <xref target="RFC5155" sectionFormat="comma" section="1.3"/>)
See <xref target="dnssec-general"/> for more on "opt-out". See <xref target="dnssec-general" format="default"/> for more on "opt-out".
</t> </dd>
<dt>Next closer name:</dt>
<t hangText='Next closer name:'> <dd>
<iref item='Next closer name'/> <iref item="Next closer name" subitem="" primary="false"/>
"The name one label longer than the closest "The name one label longer than the closest
provable encloser of a name." provable encloser of a name."
(Quoted from <xref target="RFC5155"/>, Section 1.3)</t> (Quoted from <xref target="RFC5155" sectionFormat="comma" section="1.3"/>)</dd>
<dt>Source of Synthesis:</dt>
<t hangText='Source of Synthesis:'> <dd>
<iref item='Source of Synthesis'/> <t><iref item="Source of Synthesis" subitem="" primary="false"/>
"The source of synthesis is defined in the context of a query process "The source of synthesis is defined in the context of a query process
as that wildcard domain name immediately descending from the closest as that wildcard domain name immediately descending from the closest
encloser, provided that this wildcard domain name exists. encloser, provided that this wildcard domain name exists.
'Immediately descending' means that the source of synthesis has a 'Immediately descending' means that the source of synthesis has a
name of the form: name of the form:
<vspace blankLines="0"/> </t>
<t>
&lt;asterisk label&gt;.&lt;closest encloser&gt;." &lt;asterisk label&gt;.&lt;closest encloser&gt;."
<vspace blankLines="0"/> </t>
(Quoted from <xref target="RFC4592"/>, Section 3.3.1)</t> <t>
(Quoted from <xref target="RFC4592" sectionFormat="comma" section="3.3.1"/>)</t>
</list></t> </dd>
</section> </dl>
</section>
<section anchor="reg-model" title="Registration Model"> <section anchor="reg-model" numbered="true" toc="default">
<t><list style="hanging"> <name>Registration Model</name>
<dl newline="false" spacing="normal">
<t hangText='Registry:'> <dt>Registry:</dt>
<iref item='Registry'/> <dd>
<iref item="Registry" subitem="" primary="false"/>
The administrative operation of a zone that allows registration of names within that The administrative operation of a zone that allows registration of names within that
zone. People often use this term to refer only to those organizations zone. People often use this term to refer only to those organizations
that perform registration in large delegation-centric zones (such as that perform registration in large delegation-centric zones (such as
TLDs); but formally, whoever decides what data goes into a zone is the TLDs); but formally, whoever decides what data goes into a zone is the
registry for that zone. registry for that zone.
This definition of "registry" is from a DNS point of view; for some zones, the p olicies This definition of "registry" is from a DNS point of view; for some zones, the p olicies
that determine what can go in the zone are decided by zones that are superordina that determine what can go in the zone are decided by zones that are superordina
te and not the registry operator.</t> te and not the registry operator.</dd>
<dt>Registrant:</dt>
<t hangText='Registrant:'> <dd>
<iref item='Registrant'/> <iref item="Registrant" subitem="" primary="false"/>
An individual or organization on whose behalf a name in An individual or organization on whose behalf a name in
a zone is registered by the registry. In many zones, the registry and a zone is registered by the registry. In many zones, the registry and
the registrant may be the same entity, but in TLDs they often are the registrant may be the same entity, but in TLDs they often are
not.</t> not.</dd>
<dt>Registrar:</dt>
<t hangText='Registrar:'> <dd>
<iref item='Registrar'/> <iref item="Registrar" subitem="" primary="false"/>
A service provider that acts as a go-between for A service provider that acts as a go-between for
registrants and registries. Not all registrations require a registrants and registries. Not all registrations require a
registrar, though it is common to have registrars involved in registrar, though it is common to have registrars involved in
registrations in TLDs.</t> registrations in TLDs.</dd>
<dt>EPP:</dt>
<t hangText='EPP:'> <dd>
<iref item='EPP'/> <iref item="EPP" subitem="" primary="false"/>
The Extensible Provisioning Protocol (EPP), which is commonly used for communica tion The Extensible Provisioning Protocol (EPP), which is commonly used for communica tion
of registration information between registries and registrars. EPP is defined in of registration information between registries and registrars. EPP is defined in
<xref target="RFC5730"/>.</t> <xref target="RFC5730" format="default"/>.</dd>
<dt>WHOIS:</dt>
<t hangText='WHOIS:'> <dd>
<iref item='WHOIS'/> <iref item="WHOIS" subitem="" primary="false"/>
A protocol specified in <xref target="RFC3912"/>, often used for querying regist A protocol specified in <xref target="RFC3912" format="default"/>, often used fo
ry databases. r querying registry databases.
WHOIS data is frequently used to associate registration data (such as zone manag ement WHOIS data is frequently used to associate registration data (such as zone manag ement
contacts) with domain names. contacts) with domain names.
The term "WHOIS data" is often used as a synonym for the registry database, even though The term "WHOIS data" is often used as a synonym for the registry database, even though
that database may be served by different protocols, particularly RDAP. that database may be served by different protocols, particularly RDAP.
The WHOIS protocol is also used with IP address registry data.</t> The WHOIS protocol is also used with IP address registry data.</dd>
<dt>RDAP:</dt>
<t hangText='RDAP:'> <dd>
<iref item='RDAP'/> <iref item="RDAP" subitem="" primary="false"/>
The Registration Data Access Protocol, defined in The Registration Data Access Protocol, defined in
<xref target="RFC7480"/>, <xref target="RFC7481"/>, <xref target="RFC7482"/>, <x <xref target="RFC7480" format="default"/>, <xref target="RFC7481" format="defaul
ref target="RFC7483"/>, t"/>, <xref target="RFC7485"
<xref target="RFC7484"/>, and <xref target="RFC7485"/>. format="default"/>, <xref target="RFC9082" format="default"/>, <xref target="RFC
The RDAP protocol and data format are meant as a replacement for WHOIS.</t> 9083" format="default"/>, and
<xref target="RFC9224" format="default"/>.
<t hangText='DNS operator:'> The RDAP protocol and data format are meant as a replacement for WHOIS.</dd>
<iref item='DNS operator'/> <dt>DNS operator:</dt>
<dd>
<iref item="DNS operator" subitem="" primary="false"/>
An entity responsible for running DNS servers. For a zone's authoritative server s, the registrant An entity responsible for running DNS servers. For a zone's authoritative server s, the registrant
may act as their own DNS operator, their registrar may do it on their behalf, or they may use a may act as their own DNS operator, their registrar may do it on their behalf, or they may use a
third-party operator. third-party operator.
For some zones, the registry function is performed by the DNS operator plus othe r entities For some zones, the registry function is performed by the DNS operator plus othe r entities
who decide about the allowed contents of the zone.</t> who decide about the allowed contents of the zone.</dd>
<dt>Public suffix:</dt>
<t hangText='Public suffix:'> <dd>
<iref item='Public suffix'/> <iref item="Public suffix" subitem="" primary="false"/>
"A domain that is controlled by a public registry." (Quoted from <xref target="R "A domain that is controlled by a public registry." (Quoted from <xref target="R
FC6265"/>, Section 5.3) FC6265" sectionFormat="comma" section="5.3"/>) A common definition for this term
A common definition for this term is a domain under which subdomains can be regi is a domain under which subdomains can be registered by third parties and on wh
stered by third parties and on which HTTP cookies ich HTTP cookies
(which are described in detail in <xref target="RFC6265"/>) should not be set. (which are described in detail in <xref target="RFC6265" format="default"/>) sho
uld not be set.
There is no indication in a domain name whether it is a public suffix; that can only be There is no indication in a domain name whether it is a public suffix; that can only be
determined by outside means. determined by outside means.
In fact, both a domain and a subdomain of that domain can be public suffixes. In fact, both a domain and a subdomain of that domain can be public suffixes.
</t> </dd>
<dt/>
<t>There is nothing inherent in a domain name to indicate whether it is <dd>There is nothing inherent in a domain name to indicate whether it is
a public suffix. One a public suffix. One
resource for identifying public suffixes is the Public Suffix List (PSL) resource for identifying public suffixes is the Public Suffix List (PSL)
maintained by Mozilla (https://publicsuffix.org/).</t> maintained by Mozilla <eref brackets="angle" target="https://publicsuffix.org/"/
>.</dd>
<t>For example, at the time this document is published, <dt/>
<dd>For example, at the time this document is published,
the "com.au" domain is listed as a public suffix in the PSL. the "com.au" domain is listed as a public suffix in the PSL.
(Note that this example might change in the future.)</t> (Note that this example might change in the future.)</dd>
<dt/>
<t>Note that the term "public suffix" is controversial in the DNS <dd>Note that the term "public suffix" is controversial in the DNS
community for many reasons, and it may be significantly changed in the future. O ne example of the community for many reasons, and it may be significantly changed in the future. O ne example of the
difficulty of calling a domain a public suffix is that designation can change ov er time as the difficulty of calling a domain a public suffix is that designation can change ov er time as the
registration policy for the zone changes, such as was the case with the "uk" TLD registration policy for the zone changes, such as was the case with the "uk" TLD
in 2014.</t> in 2014.</dd>
<dt>Subordinate and Superordinate:</dt>
<t hangText='Subordinate and Superordinate:'> <dd>
<iref item='Subordinate'/> <iref item="Subordinate" subitem="" primary="false"/>
<iref item='Superordinate'/> <iref item="Superordinate" subitem="" primary="false"/>
These terms are introduced in <xref target="RFC5731"/> for use in the registrati These terms are introduced in <xref target="RFC5731" format="default"/> for use
on model, but not defined there. in the registration model, but not defined there.
Instead, they are given in examples. Instead, they are given in examples.
"For example, domain name 'example.com' has a superordinate relationship to host name "For example, domain name 'example.com' has a superordinate relationship to host name
ns1.example.com'... For example, host ns1.example1.com is a subordinate host of domain example1.com, ns1.example.com'... For example, host ns1.example1.com is a subordinate host of domain example1.com,
but it is a not a subordinate host of domain example2.com." but it is a not a subordinate host of domain example2.com."
(Quoted from <xref target="RFC5731"/>, Section 1.1) (Quoted from <xref target="RFC5731" sectionFormat="comma" section="1.1"/>)
These terms are strictly ways of referring to the relationship standing of two d omains These terms are strictly ways of referring to the relationship standing of two d omains
where one is a subdomain of the other.</t> where one is a subdomain of the other.</dd>
</dl>
</list></t> </section>
</section> <section anchor="dnssec-general" numbered="true" toc="default">
<name>General DNSSEC</name>
<section anchor="dnssec-general" title="General DNSSEC"> <t>Most DNSSEC terms are defined in <xref target="RFC4033" format="default
"/>,
<t>Most DNSSEC terms are defined in <xref target="RFC4033"/>, <xref target="RFC4034" format="default"/>, <xref target="RFC4035" format="defaul
<xref target="RFC4034"/>, <xref target="RFC4035"/>, and <xref target="RFC5155"/> t"/>, and <xref target="RFC5155" format="default"/>. The
. The
terms that have caused confusion in the DNS community are highlighted here.</t> terms that have caused confusion in the DNS community are highlighted here.</t>
<dl newline="false" spacing="normal">
<t><list style="hanging"> <dt>DNSSEC-aware and DNSSEC-unaware:</dt>
<dd>
<t hangText='DNSSEC-aware and DNSSEC-unaware:'> <iref item="DNSSEC-aware and DNSSEC-unaware" subitem="" primary="false
<iref item='DNSSEC-aware and DNSSEC-unaware'/> "/>
These two terms, which are used in some RFCs, have not been formally defined. These two terms, which are used in some RFCs, have not been formally defined.
However, Section 2 of <xref target="RFC4033"/> defines many types of resolvers a nd However, <xref target="RFC4033" sectionFormat="of" section="2"/> defines many ty pes of resolvers and
validators, including "non-validating security-aware stub resolver", "non-valida ting validators, including "non-validating security-aware stub resolver", "non-valida ting
stub resolver", "security-aware name server", "security-aware recursive name ser ver", stub resolver", "security-aware name server", "security-aware recursive name ser ver",
"security-aware resolver", "security-aware stub resolver", and "security-oblivio us 'anything'". "security-aware resolver", "security-aware stub resolver", and "security-oblivio us 'anything'".
(Note that the term "validating resolver", which is used in some (Note that the term "validating resolver", which is used in some
places in DNSSEC-related documents, is also not defined in those RFCs, but is de places in DNSSEC-related documents, is also not defined in those RFCs, but is de
fined below.)</t> fined below.)</dd>
<dt>Signed zone:</dt>
<t hangText='Signed zone:'> <dd>
<iref item='Signed zone'/> <iref item="Signed zone" subitem="" primary="false"/>
"A zone whose RRsets are signed and that contains "A zone whose RRsets are signed and that contains
properly constructed DNSKEY, Resource Record Signature (RRSIG), properly constructed DNSKEY, Resource Record Signature (RRSIG),
Next Secure (NSEC), and (optionally) DS records." (Quoted from Next Secure (NSEC), and (optionally) DS records." (Quoted from
<xref target="RFC4033"/>, Section 2) <xref target="RFC4033" sectionFormat="comma" section="2"/>)
It has been noted in other contexts that the zone itself is not It has been noted in other contexts that the zone itself is not
really signed, but all the relevant RRsets in the zone are signed. really signed, but all the relevant RRsets in the zone are signed.
Nevertheless, if a zone that should be signed contains any RRsets that Nevertheless, if a zone that should be signed contains any RRsets that
are not signed (or opted out), those RRsets will be treated as bogus, are not signed (or opted out), those RRsets will be treated as bogus,
so the whole zone needs to be handled in some way.</t> so the whole zone needs to be handled in some way.</dd>
<t>It should also be noted that, since the publication of <xref target="RFC6840" <dt/>
/>, NSEC records are no
<dd>It should also be noted that, since the publication of <xref target="RFC6840
" format="default"/>, NSEC records are no
longer required for signed zones: a signed zone might include NSEC3 records inst ead. longer required for signed zones: a signed zone might include NSEC3 records inst ead.
<xref target="RFC7129"/> provides additional background commentary and some cont ext for the NSEC and <xref target="RFC7129" format="default"/> provides additional background comment ary and some context for the NSEC and
NSEC3 mechanisms used by DNSSEC to provide authenticated denial-of-existence res ponses. NSEC3 mechanisms used by DNSSEC to provide authenticated denial-of-existence res ponses.
NSEC and NSEC3 are described below.</t> NSEC and NSEC3 are described below.</dd>
<dt>Online signing:</dt>
<t hangText='Online signing:'> <dd>
<iref item='online signing'/><iref item='on-line signing'/> <iref item="online signing" subitem="" primary="false"/><iref item="on
<xref target="RFC4470"/> defines "on-line signing" (note the hyphen) as -line signing" subitem="" primary="false"/>
<xref target="RFC4470" format="default"/> defines "on-line signing" (n
ote the hyphen) as
"generating and signing these records on demand", where "these" was defined "generating and signing these records on demand", where "these" was defined
as NSEC records. The current definition expands that to as NSEC records. The current definition expands that to
generating and signing RRSIG, NSEC, and NSEC3 records on demand. generating and signing RRSIG, NSEC, and NSEC3 records on demand.
</t> </dd>
<dt>Unsigned zone:</dt>
<t hangText='Unsigned zone:'> <dd>
<iref item='Unsigned zone'/> <iref item="Unsigned zone" subitem="" primary="false"/>
Section 2 of <xref target="RFC4033"/> defines this as "a zone that is not signed <xref target="RFC4033" sectionFormat="of" section="2"/> defines this as "a zone
". Section 2 of that is not signed". <xref target="RFC4035" sectionFormat="of" section="2"/> def
<xref target="RFC4035"/> defines this as a "zone that does not include these rec ines this as a "zone that does not include these records [properly constructed D
ords [properly constructed DNSKEY, NSKEY,
Resource Record Signature (RRSIG), Next Secure (NSEC), and (optionally) DS recor ds] according to the Resource Record Signature (RRSIG), Next Secure (NSEC), and (optionally) DS recor ds] according to the
rules in this section..." There is an important note at the end of Section 5.2 of <xref target="RFC4035"/> that defines an rules in this section..." There is an important note at the end of <xref target ="RFC4035" sectionFormat="of" section="5.2"/> that defines an
additional situation in which a zone is considered unsigned: additional situation in which a zone is considered unsigned:
<!--Begin DNE -->
"If the resolver does not support any of "If the resolver does not support any of
the algorithms listed in an authenticated DS RRset, then the resolver will not b e able to verify the the algorithms listed in an authenticated DS RRset, then the resolver will not b e able to verify the
authentication path to the child zone. In this case, the resolver SHOULD treat the child zone as if authentication path to the child zone. In this case, the resolver SHOULD treat the child zone as if
it were unsigned." it were unsigned."
<!--End DNE --> </dd>
</t> <dt>NSEC:</dt>
<dd>
<t hangText='NSEC:'> <iref item="NSEC" subitem="" primary="false"/>
<iref item='NSEC'/>
"The NSEC record allows a security-aware resolver to authenticate a negative rep ly for "The NSEC record allows a security-aware resolver to authenticate a negative rep ly for
either name or type non-existence with the same mechanisms used to authenticate other DNS replies." either name or type non-existence with the same mechanisms used to authenticate other DNS replies."
(Quoted from <xref target="RFC4033"/>, Section 3.2) In short, an NSEC record pro (Quoted from <xref target="RFC4033" sectionFormat="comma" section="3.2"/>) In sh
vides authenticated denial of ort, an NSEC record provides authenticated denial of
existence.</t> existence.</dd>
<dt/>
<t>"The NSEC resource record lists two separate things: the next owner name (in <dd>"The NSEC resource record lists two separate things: the next owner
the canonical name (in the canonical
ordering of the zone) that contains authoritative data or a delegation point NS RRset, and the set ordering of the zone) that contains authoritative data or a delegation point NS RRset, and the set
of RR types present at the NSEC RR's owner name." (Quoted from Section 4 of RFC of RR types present at the NSEC RR's owner name." (Quoted from <xref target="RFC
4034)</t> 4034" sectionFormat="of" section="4"/>)</dd>
<dt>NSEC3:</dt>
<t hangText='NSEC3:'> <dd>
<iref item='NSEC3'/> <iref item="NSEC3" subitem="" primary="false"/>
Like the NSEC record, the NSEC3 record also provides authenticated denial of exi stence; however, Like the NSEC record, the NSEC3 record also provides authenticated denial of exi stence; however,
NSEC3 records mitigate zone enumeration and support Opt-Out. NSEC3 records mitigate zone enumeration and support Opt-Out.
NSEC3 resource records require associated NSEC3PARAM resource records. NSEC3 resource records require associated NSEC3PARAM resource records.
NSEC3 and NSEC3PARAM resource records are defined in <xref target="RFC5155"/>.</ NSEC3 and NSEC3PARAM resource records are defined in <xref target="RFC5155" form
t> at="default"/>.</dd>
<dt/>
<t>Note that <xref target="RFC6840"/> says that <xref target="RFC5155"/> "is now <dd>Note that <xref target="RFC6840" format="default"/> says that <xref
considered part of the DNS Security Document Family target="RFC5155" format="default"/> "is now considered part of the DNS Security
as described by Section 10 of <xref target="RFC4033"/>". This means that some of Document Family
the definitions from earlier RFCs that as described by <xref target="RFC4033" sectionFormat="of" section="10"/>". This
only talk about NSEC records should probably be considered to be talking about b means that some of the definitions from earlier RFCs that
oth NSEC and NSEC3.</t> only talk about NSEC records should probably be considered to be talking about b
oth NSEC and NSEC3.</dd>
<t hangText='Opt-out:'> <dt>Opt-out:</dt>
<iref item='Opt-out'/> <dd>
<iref item="Opt-out" subitem="" primary="false"/>
"The Opt-Out Flag indicates whether this NSEC3 RR may cover unsigned delegations ." "The Opt-Out Flag indicates whether this NSEC3 RR may cover unsigned delegations ."
(Quoted from <xref target="RFC5155"/>, Section 3.1.2.1) (Quoted from <xref target="RFC5155" sectionFormat="comma" section="3.1.2.1"/>)
Opt-out tackles the high costs of securing a delegation to an insecure zone. Wh en using Opt-out tackles the high costs of securing a delegation to an insecure zone. Wh en using
Opt-Out, names that are an insecure delegation (and empty non-terminals that are only Opt-Out, names that are an insecure delegation (and empty non-terminals that are only
derived from insecure delegations) don't require an NSEC3 record or its correspo nding derived from insecure delegations) don't require an NSEC3 record or its correspo nding
RRSIG records. Opt-Out NSEC3 records are not able to prove or deny the existence of the RRSIG records. Opt-Out NSEC3 records are not able to prove or deny the existence of the
insecure delegations. (Adapted from <xref target="RFC7129"/>, Section 5.1)</t> insecure delegations. (Adapted from <xref target="RFC7129" sectionFormat="comma"
section="5.1"/>)</dd>
<t hangText='Insecure delegation:'> <dt>Insecure delegation:</dt>
<iref item='Insecure delegation'/> <dd>
<iref item="Insecure delegation" subitem="" primary="false"/>
"A signed name containing a delegation (NS RRset), but lacking a DS RRset, "A signed name containing a delegation (NS RRset), but lacking a DS RRset,
signifying a delegation to an unsigned subzone." (Quoted from <xref target="RFC4 signifying a delegation to an unsigned subzone." (Quoted from <xref target="RFC4
956"/>, Section 2)</t> 956" sectionFormat="comma" section="2"/>)</dd>
<dt>Zone enumeration:</dt>
<t hangText='Zone enumeration:'> <dd>
<iref item='Zone enumeration'/> <iref item="Zone enumeration" subitem="" primary="false"/>
"The practice of discovering the full content of a zone via successive queries." "The practice of discovering the full content of a zone via successive queries."
(Quoted from <xref target="RFC5155"/>, Section 1.3) This is also sometimes calle d "zone walking". (Quoted from <xref target="RFC5155" sectionFormat="comma" section="1.3"/>) This is also sometimes called "zone walking".
Zone enumeration is different from zone content guessing where the guesser uses a large dictionary Zone enumeration is different from zone content guessing where the guesser uses a large dictionary
of possible labels and sends successive queries for them, or matches the content s of NSEC3 records of possible labels and sends successive queries for them, or matches the content s of NSEC3 records
against such a dictionary.</t> against such a dictionary.</dd>
<dt>Validation:</dt>
<t hangText='Validation:'> <dd>
<iref item='Validation'/> <t><iref item="Validation" subitem="" primary="false"/>
Validation, in the context of DNSSEC, refers to one of the following: Validation, in the context of DNSSEC, refers to one of the following:
<list style="symbols"> </t>
<ul spacing="normal">
<t>Checking the validity of DNSSEC signatures,</t> <li>Checking the validity of DNSSEC signatures,</li>
<li>Checking the validity of DNS responses, such as those including
<t>Checking the validity of DNS responses, such as those including authenticated authenticated denial of
denial of existence, or</li>
existence, or</t> <li>Building an authentication chain from a trust anchor to a DNS re
sponse or individual
<t>Building an authentication chain from a trust anchor to a DNS response or ind DNS RRsets in a response.</li>
ividual </ul>
DNS RRsets in a response</t> </dd>
<dt/>
</list></t> <dd>The first two definitions above consider only the validity of indivi
dual DNSSEC
<t>The first two definitions above consider only the validity of individual DNSS components, such as the RRSIG validity or NSEC proof validity. The third definit
EC ion
components such as the RRSIG validity or NSEC proof validity. The third definiti
on
considers the components of the entire DNSSEC authentication chain; thus, it req uires considers the components of the entire DNSSEC authentication chain; thus, it req uires
"configured knowledge of at least one authenticated DNSKEY or DS RR" (as describ ed in "configured knowledge of at least one authenticated DNSKEY or DS RR" (as describ ed in
<xref target="RFC4035"/>, Section 5).</t> <xref target="RFC4035" sectionFormat="comma" section="5"/>).</dd>
<dt/>
<t><xref target="RFC4033"/>, Section 2, says that a "Validating Security-Aware S <dd>
tub <xref target="RFC4033" sectionFormat="comma" section="2"/>, says that
a "Validating Security-Aware Stub
Resolver... performs signature validation" and uses a trust anchor "as a startin g point Resolver... performs signature validation" and uses a trust anchor "as a startin g point
for building the authentication chain to a signed DNS response"; thus, it uses t he first for building the authentication chain to a signed DNS response"; thus, it uses t he first
and third definitions above. The process of validating an RRSIG resource record and third definitions above. The process of validating an RRSIG resource record
is described in <xref is described in <xref target="RFC4035" sectionFormat="comma" section="5.3"/>.</
target="RFC4035"/>, Section 5.3.</t> dd>
<dt/>
<t><xref target="RFC5155"/> refers to validating responses throughout the docume <dd>
nt, in the <xref target="RFC5155" format="default"/> refers to validating respons
es throughout the document in the
context of hashed authenticated denial of existence; this uses the second defini tion context of hashed authenticated denial of existence; this uses the second defini tion
above.</t> above.</dd>
<dt/>
<t> <dd>
The term "authentication" is used interchangeably with "validation", in the sens e of the The term "authentication" is used interchangeably with "validation", in the sens e of the
third definition above. third definition above.
<xref target="RFC4033"/>, Section <xref target="RFC4033" sectionFormat="comma" section="2"/>, describes the chain
2, describes the chain linking trust anchor to DNS data as the "authentication c linking trust anchor to DNS data as the "authentication chain". A
hain". A response is considered to be authentic if "all RRsets in the Answer and
response is considered to be authentic if "all RRsets in the Answer and Authorit Authority sections
y sections of the response [are considered] to be authentic" (Quoted from <xref target="RFC
of the response [are considered] to be authentic" (Quoted from <xref target="RFC 4035" format="default"/>) DNS data or
4035"/>) DNS data or responses deemed to be authentic or validated have a security status of "secure"
responses deemed to be authentic or validated have a security status of "secure" (<xref target="RFC4035" sectionFormat="comma" section="4.3"/>; <xref target="RF
(<xref C4033" sectionFormat="comma" section="5"/>). "Authenticating
target="RFC4035"/>, Section 4.3; <xref target="RFC4033"/>, Section 5). "Authent
icating
both DNS keys and data is a matter of local policy, which may extend or even ove rride the both DNS keys and data is a matter of local policy, which may extend or even ove rride the
[DNSSEC] protocol extensions..." (Quoted from <xref target="RFC4033"/>, Section [DNSSEC] protocol extensions..." (Quoted from <xref target="RFC4033" sectionForm
3.1)</t> at="comma" section="3.1"/>)</dd>
<dt/>
<t>The term "verification", when used, is usually a synonym for "validation".</t <dd>The term "verification", when used, is usually a synonym for "valida
> tion".</dd>
<dt>Validating resolver:</dt>
<t hangText='Validating resolver:'> <dd>
<iref item='Validating resolver'/> <iref item="Validating resolver" subitem="" primary="false"/>
A security-aware recursive name server, security-aware resolver, or A security-aware recursive name server, security-aware resolver, or
security-aware stub resolver that is applying at least one of the security-aware stub resolver that is applying at least one of the
definitions of validation (above), as appropriate to the resolution definitions of validation (above) as appropriate to the resolution
context. For the same reason that the generic term "resolver" is context. For the same reason that the generic term "resolver" is
sometimes ambiguous and needs to be evaluated in context (see <xref sometimes ambiguous and needs to be evaluated in context (see <xref target="dn
target="dns-servers-and-clients" />), "validating resolver" is a s-servers-and-clients" format="default"/>), "validating resolver" is a
context-sensitive term. context-sensitive term.
</t> </dd>
<dt>Key signing key (KSK):</dt>
<t hangText='Key signing key (KSK):'> <dd>
<iref item='Key signing key (KSK)'/> <iref item="Key signing key (KSK)" subitem="" primary="false"/>
DNSSEC keys that "only sign the apex DNSKEY RRset in a zone." (Quoted from DNSSEC keys that "only sign the apex DNSKEY RRset in a zone." (Quoted from
<xref target="RFC6781"/>, Section 3.1)</t> <xref target="RFC6781" sectionFormat="comma" section="3.1"/>)</dd>
<dt>Zone signing key (ZSK):</dt>
<t hangText='Zone signing key (ZSK):'> <dd>
<iref item='Zone signing key (ZSK)'/> <iref item="Zone signing key (ZSK)" subitem="" primary="false"/>
"DNSSEC keys that can be used to sign all the RRsets in a zone that "DNSSEC keys that can be used to sign all the RRsets in a zone that
require signatures, other than the apex DNSKEY RRset." (Quoted from <xref target require signatures, other than the apex DNSKEY RRset." (Quoted from <xref target
="RFC6781"/>, Section 3.1) ="RFC6781" sectionFormat="comma" section="3.1"/>)
Also note that a ZSK is sometimes used to sign the apex DNSKEY RRset.</t> Also note that a ZSK is sometimes used to sign the apex DNSKEY RRset.</dd>
<dt>Combined signing key (CSK):</dt>
<t hangText='Combined signing key (CSK):'> <dd>
<iref item='Combined signing key (CSK)'/> <iref item="Combined signing key (CSK)" subitem="" primary="false"/>
"In cases where the differentiation between the KSK and ZSK is not made, "In cases where the differentiation between the KSK and ZSK is not made,
i.e., where keys have the role of both KSK and ZSK, we talk about a Single-Type Signing i.e., where keys have the role of both KSK and ZSK, we talk about a Single-Type Signing
Scheme." (Quoted from <xref target="RFC6781"/>, Section 3.1) This is sometimes c alled a "combined Scheme." (Quoted from <xref target="RFC6781" sectionFormat="comma" section="3.1" />) This is sometimes called a "combined
signing key" or "CSK". It is operational practice, not protocol, that determine s whether a signing key" or "CSK". It is operational practice, not protocol, that determine s whether a
particular key is a ZSK, a KSK, or a CSK.</t> particular key is a ZSK, a KSK, or a CSK.</dd>
<dt>Secure Entry Point (SEP):</dt>
<t hangText='Secure Entry Point (SEP):'> <dd>
<iref item='Secure Entry Point (SEP)'/> <iref item="Secure Entry Point (SEP)" subitem="" primary="false"/>
A flag in the DNSKEY RDATA that "can be used to distinguish between A flag in the DNSKEY RDATA that "can be used to distinguish between
keys that are intended to be used as the secure entry point into the zone when b uilding keys that are intended to be used as the secure entry point into the zone when b uilding
chains of trust, i.e., they are (to be) pointed to by parental DS RRs or configu red as a chains of trust, i.e., they are (to be) pointed to by parental DS RRs or configu red as a
trust anchor.... trust anchor....
Therefore, it is suggested that the SEP flag be set on keys that are used as KSK s and not on keys Therefore, it is suggested that the SEP flag be set on keys that are used as KSK s and not on keys
that are used as ZSKs, while in those cases where a distinction between a KSK an d ZSK is not made that are used as ZSKs, while in those cases where a distinction between a KSK an d ZSK is not made
(i.e., for a Single-Type Signing Scheme), it is suggested that the SEP flag be s et on all keys." (i.e., for a Single-Type Signing Scheme), it is suggested that the SEP flag be s et on all keys."
(Quoted from <xref target="RFC6781"/>, Section 3.2.3) Note that the (Quoted from <xref target="RFC6781" sectionFormat="comma" section="3.2.3"/>) No te that the
SEP flag is only a hint, and its presence or absence may not be used to disquali fy a given SEP flag is only a hint, and its presence or absence may not be used to disquali fy a given
DNSKEY RR from use as a KSK or ZSK during validation.</t> DNSKEY RR from use as a KSK or ZSK during validation.</dd>
<dt/>
<t>The original definition of SEPs was in <xref target="RFC3757"/>. That definit <dd>The original definition of SEPs was in <xref target="RFC3757" format
ion ="default"/>. That definition
clearly indicated that the SEP was a key, not just a bit in the key. The clearly indicated that the SEP was a key, not just a bit in the key. The
abstract of <xref target="RFC3757"/> says: abstract of <xref target="RFC3757" format="default"/> says:
"With the Delegation Signer (DS) resource record (RR), the concept of "With the Delegation Signer (DS) resource record (RR), the concept of
a public key acting as a secure entry point (SEP) has been a public key acting as a secure entry point (SEP) has been
introduced. During exchanges of public keys with the parent there is introduced. During exchanges of public keys with the parent there is
a need to differentiate SEP keys from other public keys in the Domain a need to differentiate SEP keys from other public keys in the Domain
Name System KEY (DNSKEY) resource record set. A flag bit in the Name System KEY (DNSKEY) resource record set. A flag bit in the
DNSKEY RR is defined to indicate that DNSKEY is to be used as a SEP." DNSKEY RR is defined to indicate that DNSKEY is to be used as a SEP."
That definition of the SEP as a key was made obsolete by <xref target="RFC4034"/ That definition of the SEP as a key was made obsolete by <xref target="RFC4034"
>, format="default"/>,
and the definition from <xref target="RFC6781"/> is consistent with <xref target and the definition from <xref target="RFC6781" format="default"/> is consistent
="RFC4034"/>.</t> with <xref target="RFC4034" format="default"/>.</dd>
<dt>Trust anchor:</dt>
<t hangText='Trust anchor:'> <dd>
<iref item='Trust anchor'/> <iref item="Trust anchor" subitem="" primary="false"/>
"A configured DNSKEY RR or DS RR hash of a DNSKEY RR. A "A configured DNSKEY RR or DS RR hash of a DNSKEY RR. A
validating security-aware resolver uses this public key or hash as validating security-aware resolver uses this public key or hash as
a starting point for building the authentication chain to a signed a starting point for building the authentication chain to a signed
DNS response. In general, a validating resolver will have to DNS response. In general, a validating resolver will have to
obtain the initial values of its trust anchors via some secure or obtain the initial values of its trust anchors via some secure or
trusted means outside the DNS protocol." (Quoted from <xref target="RFC4033"/>, trusted means outside the DNS protocol." (Quoted from <xref target="RFC4033" sec
Section 2)</t> tionFormat="comma" section="2"/>)</dd>
<dt>DNSSEC Policy (DP):</dt>
<t hangText='DNSSEC Policy (DP):'> <dd>
<iref item='DNSSEC Policy (DP)'/> <iref item="DNSSEC Policy (DP)" subitem="" primary="false"/>
A statement that "sets forth the security requirements and A statement that "sets forth the security requirements and
standards to be implemented for a DNSSEC-signed zone." (Quoted from <xref target standards to be implemented for a DNSSEC-signed zone." (Quoted from <xref target
="RFC6841"/>, ="RFC6841" sectionFormat="comma" section="2"/>)</dd>
Section 2)</t> <dt>DNSSEC Practice Statement (DPS):</dt>
<dd>
<t hangText='DNSSEC Practice Statement (DPS):'> <iref item="DNSSEC Practice Statement (DPS)" subitem="" primary="false
<iref item='DNSSEC Practice Statement (DPS)'/>"A practices disclosure document t "/>"A practices disclosure document that may
hat may
support and be a supplemental document to the DNSSEC Policy (if such exists), support and be a supplemental document to the DNSSEC Policy (if such exists),
and it states how the management of a given zone implements procedures and and it states how the management of a given zone implements procedures and
controls at a high level." (Quoted from <xref target="RFC6841"/>, Section 2)</t> controls at a high level." (Quoted from <xref target="RFC6841" sectionFormat="co
mma" section="2"/>)</dd>
<t hangText='Hardware security module (HSM):'> <dt>Hardware security module (HSM):</dt>
<iref item='Hardware security module (HSM)'/> <dd>
<iref item="Hardware security module (HSM)" subitem="" primary="false"
/>
A specialized piece of hardware that is used to create keys for signatures and t o A specialized piece of hardware that is used to create keys for signatures and t o
sign messages without ever disclosing the private key. In DNSSEC, HSMs are often used to hold the private keys for sign messages without ever disclosing the private key. In DNSSEC, HSMs are often used to hold the private keys for
KSKs and ZSKs and to create the signatures used in RRSIG records at periodic int KSKs and ZSKs and to create the signatures used in RRSIG records at periodic int
ervals.</t> ervals.</dd>
<dt>Signing software:</dt>
<t hangText='Signing software:'> <dd>
<iref item='Signing software'/> <iref item="Signing software" subitem="" primary="false"/>
Authoritative DNS servers that support DNSSEC often contain software that Authoritative DNS servers that support DNSSEC often contain software that
facilitates the creation and maintenance of DNSSEC signatures in zones. facilitates the creation and maintenance of DNSSEC signatures in zones.
There is also stand-alone software that can be used to sign a zone regardless There is also stand-alone software that can be used to sign a zone regardless
of whether the authoritative server itself supports signing. Sometimes of whether the authoritative server itself supports signing. Sometimes
signing software can support particular HSMs as part of the signing process.</t> signing software can support particular HSMs as part of the signing process.</dd
>
</list></t> </dl>
</section> </section>
<section anchor="dnssec-states" numbered="true" toc="default">
<section anchor="dnssec-states" title="DNSSEC States"> <name>DNSSEC States</name>
<t>A validating resolver can determine that a response is in one of four s
<t>A validating resolver can determine that a response is in one of four states: tates:
secure, insecure, bogus, or indeterminate. These states are defined in secure, insecure, bogus, or indeterminate. These states are defined in
<xref target="RFC4033"/> and <xref target="RFC4035"/>, although the definitions in the two documents differ a bit. This document makes no effort to reconcile t he definitions in the two documents, and takes no <xref target="RFC4033" format="default"/> and <xref target="RFC4035" format="def ault"/>, although the definitions in the two documents differ a bit. This docum ent makes no effort to reconcile the definitions in the two documents and takes no
position as to whether they need to be reconciled.</t> position as to whether they need to be reconciled.</t>
<t><xref target="RFC4033" sectionFormat="of" section="5"/> says:</t>
<!--Begin DNE text --> <blockquote><t>A validating resolver can determine the following 4 states:</t>
<t>Section 5 of <xref target="RFC4033"/> says:</t>
<figure><artwork><![CDATA[
A validating resolver can determine the following 4 states:
Secure: The validating resolver has a trust anchor, has a chain <dl>
<dt>Secure:</dt><dd>The validating resolver has a trust anchor, has a chain
of trust, and is able to verify all the signatures in the of trust, and is able to verify all the signatures in the
response. response.</dd>
Insecure: The validating resolver has a trust anchor, a chain <dt>Insecure:</dt><dd>The validating resolver has a trust anchor, a chain
of trust, and, at some delegation point, signed proof of the of trust, and, at some delegation point, signed proof of the
non-existence of a DS record. This indicates that subsequent non-existence of a DS record. This indicates that subsequent
branches in the tree are provably insecure. A validating branches in the tree are provably insecure. A validating
resolver may have a local policy to mark parts of the domain resolver may have a local policy to mark parts of the domain
space as insecure. space as insecure.</dd>
Bogus: The validating resolver has a trust anchor and a secure <dt>Bogus:</dt><dd>The validating resolver has a trust anchor and a secure
delegation indicating that subsidiary data is signed, but delegation indicating that subsidiary data is signed, but
the response fails to validate for some reason: missing the response fails to validate for some reason: missing
signatures, expired signatures, signatures with unsupported signatures, expired signatures, signatures with unsupported
algorithms, data missing that the relevant NSEC RR says algorithms, data missing that the relevant NSEC RR says
should be present, and so forth. should be present, and so forth.</dd>
Indeterminate: There is no trust anchor that would indicate that a <dt>Indeterminate:</dt><dd>There is no trust anchor that would indicate that a
specific portion of the tree is secure. This is the default specific portion of the tree is secure. This is the default
operation mode. operation mode.</dd>
]]></artwork></figure> </dl>
</blockquote>
<t>Section 4.3 of <xref target="RFC4035"/> says:</t> <t><xref target="RFC4035" sectionFormat="of" section="4.3"/> says:</t>
<blockquote>
<figure><artwork><![CDATA[ <t>A security-aware resolver must be able to distinguish between four
A security-aware resolver must be able to distinguish between four cases:</t>
cases:
Secure: An RRset for which the resolver is able to build a chain <dl>
<dt>Secure:</dt><dd>An RRset for which the resolver is able to build a chain
of signed DNSKEY and DS RRs from a trusted security anchor to of signed DNSKEY and DS RRs from a trusted security anchor to
the RRset. In this case, the RRset should be signed and is the RRset. In this case, the RRset should be signed and is
subject to signature validation, as described above. subject to signature validation, as described above.</dd>
Insecure: An RRset for which the resolver knows that it has no <dt>Insecure:</dt><dd>An RRset for which the resolver knows that it has no
chain of signed DNSKEY and DS RRs from any trusted starting chain of signed DNSKEY and DS RRs from any trusted starting
point to the RRset. This can occur when the target RRset lies point to the RRset. This can occur when the target RRset lies
in an unsigned zone or in a descendent [sic] of an unsigned in an unsigned zone or in a descendent [sic] of an unsigned
zone. In this case, the RRset may or may not be signed, but zone. In this case, the RRset may or may not be signed, but
the resolver will not be able to verify the signature. the resolver will not be able to verify the signature.</dd>
Bogus: An RRset for which the resolver believes that it ought to <dt>Bogus:</dt><dd>An RRset for which the resolver believes that it ought to
be able to establish a chain of trust but for which it is be able to establish a chain of trust but for which it is
unable to do so, either due to signatures that for some reason unable to do so, either due to signatures that for some reason
fail to validate or due to missing data that the relevant fail to validate or due to missing data that the relevant
DNSSEC RRs indicate should be present. This case may indicate DNSSEC RRs indicate should be present. This case may indicate
an attack but may also indicate a configuration error or some an attack but may also indicate a configuration error or some
form of data corruption. form of data corruption.</dd>
Indeterminate: An RRset for which the resolver is not able to <dt>Indeterminate:</dt><dd>An RRset for which the resolver is not able to
determine whether the RRset should be signed, as the resolver determine whether the RRset should be signed, as the resolver
is not able to obtain the necessary DNSSEC RRs. This can occur is not able to obtain the necessary DNSSEC RRs. This can occur
when the security-aware resolver is not able to contact when the security-aware resolver is not able to contact
security-aware name servers for the relevant zones. security-aware name servers for the relevant zones.</dd>
]]></artwork></figure> </dl>
</blockquote>
<!--End DNE -->
</section>
<section anchor="securitycons" title="Security Considerations">
<t>These definitions do not change any security considerations for either the gl
obal DNS or the private DNS.</t>
</section>
<section anchor="ianacons" title="IANA Considerations">
<t>Any reference to RFC 8499 in the IANA registries should be replaced with a re
ference to this document.</t>
</section> </section>
<section anchor="securitycons" numbered="true" toc="default">
<name>Security Considerations</name>
<t>These definitions do not change any security considerations for either
the global DNS or private DNS.</t>
</section>
<section anchor="ianacons" numbered="true" toc="default">
<name>IANA Considerations</name>
<t>References to RFC 8499 in the IANA registries have been replaced with r
eferences to this document.</t>
</section>
</middle>
<back>
</middle> <displayreference target="RFC0020" to="RFC20"/>
<displayreference target="RFC0819" to="RFC819"/>
<back> <displayreference target="RFC0952" to="RFC952"/>
<references title='Normative References'>
<reference anchor="IANA_RootFiles" target="https://www.iana.org/domains/root/fil
es">
<front><title>Root Files</title>
<author><organization>IANA</organization></author><date/></front>
</reference>
<?rfc include="reference.RFC.0882.xml" ?>
<?rfc include="reference.RFC.1034.xml" ?>
<?rfc include="reference.RFC.1035.xml" ?>
<?rfc include="reference.RFC.1123.xml" ?>
<?rfc include="reference.RFC.1912.xml" ?>
<?rfc include="reference.RFC.1996.xml" ?>
<?rfc include="reference.RFC.2136.xml" ?>
<?rfc include="reference.RFC.2181.xml" ?>
<?rfc include="reference.RFC.2182.xml" ?>
<?rfc include="reference.RFC.2308.xml" ?>
<?rfc include="reference.RFC.4033.xml" ?>
<?rfc include="reference.RFC.4034.xml" ?>
<?rfc include="reference.RFC.4035.xml" ?>
<?rfc include="reference.RFC.4592.xml" ?>
<?rfc include="reference.RFC.5155.xml" ?>
<?rfc include="reference.RFC.5358.xml" ?>
<?rfc include="reference.RFC.5730.xml" ?>
<?rfc include="reference.RFC.5731.xml" ?>
<?rfc include="reference.RFC.5855.xml" ?>
<?rfc include="reference.RFC.5936.xml" ?>
<?rfc include="reference.RFC.6561.xml" ?>
<?rfc include="reference.RFC.6781.xml" ?>
<?rfc include="reference.RFC.6840.xml" ?>
<?rfc include="reference.RFC.6841.xml" ?>
<?rfc include="reference.RFC.6891.xml" ?>
<?rfc include="reference.RFC.7344.xml" ?>
<?rfc include="reference.RFC.7719.xml" ?>
<?rfc include="reference.RFC.8310.xml" ?>
<?rfc include="reference.RFC.8499.xml" ?>
<?rfc include="reference.RFC.9250.xml" ?>
<?rfc include="reference.I-D.ietf-dnsop-glue-is-not-optional.xml"?>
</references>
<references title='Informative References'>
<reference anchor="IANA_Resource_Registry" target="https://www.iana.org/assignme
nts/dns-parameters/">
<front><title>Resource Record (RR) TYPEs</title>
<author><organization>IANA</organization></author><date/></front>
</reference>
<?rfc include="reference.RFC.0819.xml" ?>
<?rfc include="reference.RFC.0952.xml" ?>
<?rfc include="reference.RFC.1713.xml" ?>
<?rfc include="reference.RFC.1995.xml" ?>
<?rfc include="reference.RFC.2775.xml" ?>
<?rfc include="reference.RFC.3172.xml" ?>
<?rfc include="reference.RFC.3425.xml" ?>
<?rfc include="reference.RFC.3493.xml" ?>
<?rfc include="reference.RFC.3757.xml" ?>
<?rfc include="reference.RFC.3912.xml" ?>
<?rfc include="reference.RFC.4470.xml" ?>
<?rfc include="reference.RFC.4641.xml" ?>
<?rfc include="reference.RFC.4697.xml" ?>
<?rfc include="reference.RFC.4786.xml" ?>
<?rfc include="reference.RFC.4956.xml" ?>
<?rfc include="reference.RFC.5625.xml" ?>
<?rfc include="reference.RFC.5890.xml" ?>
<?rfc include="reference.RFC.5891.xml" ?>
<?rfc include="reference.RFC.5892.xml" ?>
<?rfc include="reference.RFC.5893.xml" ?>
<?rfc include="reference.RFC.5894.xml" ?>
<?rfc include="reference.RFC.6055.xml" ?>
<?rfc include="reference.RFC.6265.xml" ?>
<?rfc include="reference.RFC.6303.xml" ?>
<?rfc include="reference.RFC.6335.xml" ?>
<?rfc include="reference.RFC.6365.xml" ?>
<?rfc include="reference.RFC.6672.xml" ?>
<?rfc include="reference.RFC.6762.xml" ?>
<?rfc include="reference.RFC.7129.xml" ?>
<?rfc include="reference.RFC.7480.xml" ?>
<?rfc include="reference.RFC.7481.xml" ?>
<?rfc include="reference.RFC.7482.xml" ?>
<?rfc include="reference.RFC.7483.xml" ?>
<?rfc include="reference.RFC.7484.xml" ?>
<?rfc include="reference.RFC.7485.xml" ?>
<?rfc include="reference.RFC.7858.xml" ?>
<?rfc include="reference.RFC.7793.xml" ?>
<?rfc include="reference.RFC.8094.xml" ?>
<?rfc include="reference.RFC.8109.xml" ?>
<?rfc include="reference.RFC.8484.xml" ?>
<?rfc include="reference.RFC.9103.xml" ?>
<reference anchor="RSSAC026" target="https://www.icann.org/en/system/files/files
/rssac-026-14mar17-en.pdf">
<front><title>RSSAC Lexicon</title>
<author><organization>Root Server System Advisory Committee (RSSAC)</organizatio
n></author><date year="2017"/></front>
</reference>
</references>
<section anchor="updates-list" title="Definitions Updated by This Document"> <references>
<name>References</name>
<references>
<name>Normative References</name>
<t>The following definitions from RFCs are updated by this document: <reference anchor="IANA_RootFiles" target="https://www.iana.org/domains/
root/files">
<front>
<title>Root Files</title>
<author>
<organization>IANA</organization>
</author>
<date/>
</front>
</reference>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.0
882.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.1
034.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.1
035.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.1
123.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.1
912.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.1
996.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2
136.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2
181.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2
182.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2
308.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.4
033.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.4
034.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.4
035.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.4
592.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5
155.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5
358.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5
730.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5
731.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5
855.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5
936.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6
561.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6
781.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6
840.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6
841.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6
891.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7
344.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7
719.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8
310.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8
499.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9
250.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9
471.xml"/>
<list style="symbols"> </references>
<references>
<name>Informative References</name>
<t>Forwarder in <xref target="RFC2308"/></t> <reference anchor="IANA_Resource_Registry" target="https://www.iana.org/
assignments/dns-parameters/">
<front>
<title>Resource Record (RR) TYPEs</title>
<author>
<organization>IANA</organization>
</author>
<date/>
</front>
</reference>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.0
020.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.0
819.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.0
952.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.1
713.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.1
995.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2
775.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.3
172.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.3
425.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.3
493.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.3
757.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.3
912.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.4
470.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.4
641.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.4
697.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.4
786.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.4
956.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5
625.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5
890.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5
891.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5
892.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5
893.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5
894.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6
055.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6
265.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6
303.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6
335.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6
365.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6
672.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6
762.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7
129.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7
480.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7
481.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9
082.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9
083.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9
224.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7
485.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7
793.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7
858.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8
094.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8
109.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8
484.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9
103.xml"/>
<t>QNAME in <xref target="RFC2308"/></t> <reference anchor="RSSAC026" target="https://www.icann.org/en/system/fil
es/files/rssac-026-14mar17-en.pdf">
<front>
<title>RSSAC0226 RSSAC Lexicon</title>
<author>
<organization>Root Server System Advisory Committee (RSSAC)</organ
ization>
</author>
<date year="2017"/>
</front>
</reference>
</references>
</references>
<section anchor="updates-list" numbered="true" toc="default">
<name>Definitions Updated by This Document</name>
<t>The following definitions from RFCs are updated by this document:
<t>Secure Entry Point (SEP) in <xref target="RFC3757"/>; </t>
<ul spacing="normal">
<li>Forwarder in <xref target="RFC2308" format="default"/></li>
<li>QNAME in <xref target="RFC2308" format="default"/></li>
<li>Secure Entry Point (SEP) in <xref target="RFC3757" format="default"/
>;
note, however, that this RFC is already obsolete note, however, that this RFC is already obsolete
(see <xref target="RFC4033"/>, <xref target="RFC4034"/>, <xref target="RFC4035"/ (see <xref target="RFC4033" format="default"/>, <xref target="RFC4034" format="d
>).</t> efault"/>, <xref target="RFC4035" format="default"/>).</li>
</ul>
</list></t> </section>
<section anchor="new-def" numbered="true" toc="default">
</section> <name>Definitions First Defined in This Document</name>
<t>The following definitions are first defined in this document:
<section anchor="new-def" title="Definitions First Defined in This Document">
<t>The following definitions are first defined in this document:
<list style="symbols">
<t>"Alias" in <xref target="names"/></t>
<t>"Apex" in <xref target="zones"/></t>
<t>"arpa" in <xref target="zones"/></t>
<t>"Authoritative DoT (ADot)" in <xref target="dns-servers-and-clients"/></t>
<t>"Bailiwick" in <xref target="zones"/></t>
<t>"Class independent" in <xref target="rrs"/></t>
<t>"Classic DNS" in <xref target="dns-servers-and-clients"/></t>
<t>"Delegation-centric zone" in <xref target="zones"/></t>
<t>"Delegation" in <xref target="zones"/></t>
<t>"DNS operator" in <xref target="reg-model"/></t>
<t>"DNSSEC-aware" in <xref target="dnssec-general"/></t>
<t>"DNSSEC-unaware" in <xref target="dnssec-general"/></t>
<t>"Forwarding" in <xref target="dns-servers-and-clients"/></t>
<t>"Full resolver" in <xref target="dns-servers-and-clients"/></t>
<t>"Fully-qualified domain name" in <xref target="names"/></t>
<t>"Global DNS" in <xref target="names"/></t>
<t>"Hardware Security Module (HSM)" in <xref target="dnssec-general"/></t>
<t>"Host name" in <xref target="names"/></t>
<t>"IDN" in <xref target="names"/></t>
<t>"In-domain" in <xref target="zones"/></t>
<t>"Iterative resolution" in <xref target="dns-servers-and-clients"/></t>
<t>"Label" in <xref target="names"/></t>
<t>"Locally served DNS zone" in <xref target="names"/></t>
<t>"Naming system" in <xref target="names"/></t>
<t>"Negative response" in <xref target="dns-response-codes"/></t>
<t>"Non-recursive query" in <xref target="dns-servers-and-clients"/></t>
<t>"Open resolver" in <xref target="dns-servers-and-clients"/></t>
<t>"Passive DNS" in <xref target="dns-servers-and-clients"/></t>
<t>"Policy-implementing resolver" in <xref target="dns-servers-and-clients"/></t
>
<t>"Presentation format" in <xref target="rrs"/></t>
<t>"Priming" in <xref target="dns-servers-and-clients"/></t>
<t>"Private DNS" in <xref target="names"/></t>
<t>"Recrusive DoT (RDot)" in <xref target="dns-servers-and-clients"/></t>
<t>"Recursive resolver" in <xref target="dns-servers-and-clients"/></t>
<t>"Referrals" in <xref target="dns-transactions"/></t>
<t>"Registrant" in <xref target="reg-model"/></t>
<t>"Registrar" in <xref target="reg-model"/></t>
<t>"Registry" in <xref target="reg-model"/></t>
<t>"Root zone" in <xref target="zones"/></t>
<t>"Secure Entry Point (SEP)" in <xref target="dnssec-general"/></t>
<t>"Sibling domain" in <xref target="zones"/></t>
<t>"Signing software" in <xref target="dnssec-general"/></t>
<t>"Split DNS" in <xref target="dns-servers-and-clients"/></t>
<t>"Stub resolver" in <xref target="dns-servers-and-clients"/></t>
<t>"Subordinate" in <xref target="wildcards"/></t>
<t>"Superordinate" in <xref target="wildcards"/></t>
<t>"TLD" in <xref target="names"/></t>
<t>"Validating resolver" in <xref target="dnssec-general"/></t>
<t>"Validation" in <xref target="dnssec-general"/></t>
<t>"View" in <xref target="dns-servers-and-clients"/></t>
<t>"Zone transfer" in <xref target="dns-servers-and-clients"/></t>
</list></t>
</section>
<section anchor="acknowledgements" title="Acknowledgements" numbered="no">
<t>RFC 8499 and its predecessor, RFC 7719, were co-authored by Andrew Sullivan. </t>
The current document, which is a small update to RFC 8499, has just two authors. <ul spacing="normal">
<li>"Alias" in <xref target="names" format="default"/></li>
<li>"Apex" in <xref target="zones" format="default"/></li>
<li>"arpa" in <xref target="zones" format="default"/></li>
<li>"Authoritative DoT (ADot)" in <xref target="dns-servers-and-clients"
format="default"/></li>
<li>"Bailiwick" in <xref target="zones" format="default"/></li>
<li>"Class independent" in <xref target="rrs" format="default"/></li>
<li>"Classic DNS" in <xref target="dns-servers-and-clients" format="defa
ult"/></li>
<li>"Delegation-centric zone" in <xref target="zones" format="default"/>
</li>
<li>"Delegation" in <xref target="zones" format="default"/></li>
<li>"DNS operator" in <xref target="reg-model" format="default"/></li>
<li>"DNSSEC-aware" in <xref target="dnssec-general" format="default"/></
li>
<li>"DNSSEC-unaware" in <xref target="dnssec-general" format="default"/>
</li>
<li>"Forwarding" in <xref target="dns-servers-and-clients" format="defau
lt"/></li>
<li>"Full resolver" in <xref target="dns-servers-and-clients" format="de
fault"/></li>
<li>"Fully Qualified Domain Name" in <xref target="names" format="defaul
t"/></li>
<li>"Global DNS" in <xref target="names" format="default"/></li>
<li>"Hardware Security Module (HSM)" in <xref target="dnssec-general" fo
rmat="default"/></li>
<li>"Host name" in <xref target="names" format="default"/></li>
<li>"IDN" in <xref target="names" format="default"/></li>
<li>"In-domain" in <xref target="zones" format="default"/></li>
<li>"Iterative resolution" in <xref target="dns-servers-and-clients" for
mat="default"/></li>
<li>"Label" in <xref target="names" format="default"/></li>
<li>"Locally served DNS zone" in <xref target="names" format="default"/>
</li>
<li>"Naming system" in <xref target="names" format="default"/></li>
<li>"Negative response" in <xref target="dns-response-codes" format="def
ault"/></li>
<li>"Non-recursive query" in <xref target="dns-servers-and-clients" form
at="default"/></li>
<li>"Open resolver" in <xref target="dns-servers-and-clients" format="de
fault"/></li>
<li>"Passive DNS" in <xref target="dns-servers-and-clients" format="defa
ult"/></li>
<li>"Policy-implementing resolver" in <xref target="dns-servers-and-clie
nts" format="default"/></li>
<li>"Presentation format" in <xref target="rrs" format="default"/></li>
<li>"Priming" in <xref target="dns-servers-and-clients" format="default"
/></li>
<li>"Private DNS" in <xref target="names" format="default"/></li>
<li>"Recursive DoT (RDot)" in <xref target="dns-servers-and-clients" for
mat="default"/></li>
<li>"Recursive resolver" in <xref target="dns-servers-and-clients" forma
t="default"/></li>
<li>"Referrals" in <xref target="dns-transactions" format="default"/></l
i>
<li>"Registrant" in <xref target="reg-model" format="default"/></li>
<li>"Registrar" in <xref target="reg-model" format="default"/></li>
<li>"Registry" in <xref target="reg-model" format="default"/></li>
<li>"Root zone" in <xref target="zones" format="default"/></li>
<li>"Secure Entry Point (SEP)" in <xref target="dnssec-general" format="
default"/></li>
<li>"Sibling domain" in <xref target="zones" format="default"/></li>
<li>"Signing software" in <xref target="dnssec-general" format="default"
/></li>
<li>"Split DNS" in <xref target="dns-servers-and-clients" format="defaul
t"/></li>
<li>"Stub resolver" in <xref target="dns-servers-and-clients" format="de
fault"/></li>
<li>"Subordinate" in <xref target="wildcards" format="default"/></li>
<li>"Superordinate" in <xref target="wildcards" format="default"/></li>
<li>"TLD" in <xref target="names" format="default"/></li>
<li>"Validating resolver" in <xref target="dnssec-general" format="defau
lt"/></li>
<li>"Validation" in <xref target="dnssec-general" format="default"/></li
>
<li>"View" in <xref target="dns-servers-and-clients" format="default"/><
/li>
<li>"Zone transfer" in <xref target="dns-servers-and-clients" format="de
fault"/></li>
</ul>
</section>
<section anchor="acknowledgements" numbered="false" toc="default">
<name>Acknowledgements</name>
<t><xref target="RFC8499"/> and its predecessor, <xref target="RFC7719"/>,
were co-authored by <contact fullname="Andrew Sullivan"/>.
The current document, which is a small update to <xref target="RFC8499"/>, has j
ust two authors.
Andrew's work on the earlier documents is greatly appreciated.</t> Andrew's work on the earlier documents is greatly appreciated.</t>
<t>Numerous people made significant contributions to <xref target="RFC8499
<t>Numerous people made significant contributions to RFC 8499 and RFC 7719. "/> and <xref target="RFC7719"/>.
Please see the acknowledgements sections in those two documents for the Please see the acknowledgements sections in those two documents for the
extensive list of contributors.</t> extensive list of contributors.</t>
<t>Even though the current document is a small revision, many people in th
<t>Even though the current document is a small revision, many people in the e
DNSOP Working Group have contributed to it, and their work is greatly appreciate d.</t> DNSOP Working Group have contributed to it, and their work is greatly appreciate d.</t>
</section>
</section> </back>
</back>
</rfc> </rfc>
 End of changes. 316 change blocks. 
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