Diff: rfc9077.original.xml

	rfc9077.original.xml	rfc9077.xml

	<?xml version="1.0" encoding="utf-8"?>	<?xml version="1.0" encoding="UTF-8"?>
	<!-- name="GENERATOR" content="github.com/mmarkdown/mmark Mmark Markdown Process	<!DOCTYPE rfc SYSTEM "rfc2629-xhtml.ent">
	or - mmark.miek.nl" -->
	<rfc version="3" ipr="trust200902" docName="draft-ietf-dnsop-nsec-ttl-05" submis
	sionType="IETF" category="std" xml:lang="en" xmlns:xi="http://www.w3.org/2001/XI
	nclude" updates="4034, 4035, 5155, 8198" consensus="true">


	<front>	<rfc version="3" ipr="trust200902" docName="draft-ietf-dnsop-nsec-ttl-05" numbe
	<title abbrev="nsec-ttl">NSEC and NSEC3 TTLs and NSEC Aggressive Use</title><ser	r="9077" submissionType="IETF" category="std" consensus="true" xml:lang="en" xml
	iesInfo value="draft-ietf-dnsop-nsec-ttl-05" stream="IETF" status="standard" nam	ns:xi="http://www.w3.org/2001/XInclude" updates="4034, 4035, 5155, 8198" symRefs
	e="Internet-Draft"></seriesInfo>	="true" sortRefs="true" tocInclude="true">
	<author initials="P." surname="van Dijk" fullname="Peter van Dijk"><organization
	>PowerDNS</organization><address><postal><street></street>
	<city>Den Haag</city>
	<country>Netherlands</country>
	</postal><email>peter.van.dijk@powerdns.com</email>
	</address></author>
	<date/>
	<area>General</area>
	<workgroup>dnsop</workgroup>
	<keyword>Internet-Draft</keyword>


	<abstract>	<front>
	<t>Due to a combination of unfortunate wording in earlier documents, aggressive
	use of NSEC and NSEC3 records may deny the existence of names far beyond the int
	ended lifetime of a denial.
	This document changes the definition of the NSEC and NSEC3 TTL (Time To Live) to
	correct that situation.
	This document updates RFC 4034, RFC 4035, RFC 5155, and RFC 8198.</t>
	</abstract>


	</front>	<title abbrev="NSEC TTL">NSEC and NSEC3: TTLs and Aggressive Use</title>


	<middle>	<seriesInfo name="RFC" value="9077"/>


	<section anchor="introduction"><name>Introduction</name>	<author initials="P." surname="van Dijk" fullname="Peter van Dijk"><organizatio
	<t>[RFC editor: please remove this block before publication.</t>	n>PowerDNS</organization>
	<t>Earlier notes on this:</t>	<address>
		<postal>
		<street></street>
		<city>Den Haag</city>
		<country>Netherlands</country>
		</postal>
		<email>peter.van.dijk@powerdns.com</email>
		</address>
		</author>
		<date year="2021" month="July" />
		<area>General</area>
		<workgroup>dnsop</workgroup>
		<keyword>DNSSEC</keyword>
		<keyword>negative cache</keyword>
		<keyword>Denial of Existence</keyword>


	<ul>	<abstract>
	<li><eref target="https://indico.dns-oarc.net/event/29/sessions/98/#20181013">ht	<t>Due to a combination of unfortunate wording in earlier documents, aggressive
	tps://indico.dns-oarc.net/event/29/sessions/98/#20181013</eref></li>	use of NSEC and NSEC3 records may deny the existence of names far beyond the in
	<li><eref target="https://lists.dns-oarc.net/pipermail/dns-operations/2018-April	tended lifetime of a denial.
	/thread.html#17420">https://lists.dns-oarc.net/pipermail/dns-operations/2018-Apr	This document changes the definition of the NSEC and NSEC3 TTL to correct that
	il/thread.html#17420</eref></li>	situation.
	<li><eref target="https://lists.dns-oarc.net/pipermail/dns-operations/2018-March	This document updates RFCs 4034, 4035, 5155, and 8198.</t>
	/017416.html">https://lists.dns-oarc.net/pipermail/dns-operations/2018-March/017	</abstract>
	416.html</eref></li>
	</ul>
	<t>This document lives <eref target="https://github.com/PowerDNS/draft-dnsop-nse
	c-ttl">on GitHub</eref>; proposed text and editorial changes are very much welco
	med there, but any functional changes should always first be discussed on the IE
	TF DNSOP WG mailing list.</t>
	<t>]</t>
	<t><xref target="RFC2308"></xref> defines the TTL of the SOA (Start Of Authority
	) record that must be returned in negative answers (NXDOMAIN or NODATA):</t>
	<blockquote><t>The TTL of this record is set from the minimum of the MINIMUM fie
	ld of the SOA record and the TTL of the SOA itself, and indicates how long a res
	olver may cache the negative answer.</t>
	</blockquote><t>Thus, if the TTL of the SOA in the zone is lower than the SOA MI
	NIMUM value (the last number in the SOA record),
	the authoritative server sends that lower value as the TTL of the returned SOA r
	ecord.
	The resolver always uses the TTL of the returned SOA record when setting the neg
	ative TTL in its cache.</t>
	<t>However, <xref target="RFC4034"></xref> section 4 has this unfortunate text:<
	/t>
	<blockquote><t>The NSEC RR SHOULD have the same TTL value as the SOA minimum TTL
	field. This is in the spirit of negative caching ([RFC2308]).</t>
	</blockquote><t>This text, while referring to RFC2308, can cause NSEC records to
	have much higher TTLs than the appropriate negative TTL for a zone.
	<xref target="RFC5155"></xref> contains equivalent text.</t>
	<t><xref target="RFC8198"></xref> section 5.4 tries to correct this:</t>
	<blockquote><t>Section 5 of [RFC2308] also states that a negative cache entry TT
	L is taken from the minimum of the SOA.MINIMUM field and SOA's TTL. This can be
	less than the TTL of an NSEC or NSEC3 record, since their TTL is equal to the S
	OA.MINIMUM field (see <xref target="RFC4035"></xref>, Section 2.3 and [RFC5155],
	Section 3).</t>
	<t>A resolver that supports aggressive use of NSEC and NSEC3 SHOULD reduce the T
	TL of NSEC and NSEC3 records to match the SOA.MINIMUM field in the authority sec
	tion of a negative response, if SOA.MINIMUM is smaller.</t>
	</blockquote><t>But the NSEC and NSEC3 RRs should, according to RFC4034 and RFC5
	155, already be at the value of the MINIMUM field in the SOA. Thus, the advice f
	rom RFC8198 would not actually change the TTL used for the NSEC and NSEC3 RRs fo
	r authoritative servers that follow the RFCs.</t>
	<t>As a theoretical exercise, consider a TLD named <tt>.example</tt> with a SOA
	record like this:</t>
	<t><tt>example. 900 IN SOA primary.example. hostmaster.example. 1 1800 900 6
	04800 86400</tt></t>
	<t>The SOA record has a 900 second TTL, and a 86400 MINIMUM TTL.
	Negative responses from this zone have a 900 second TTL, but the NSEC or NSEC3 r
	ecords in those negative responses have a 86400 TTL.
	If a resolver were to use those NSEC or NSEC3 records aggressively, they would b
	e considered valid for a day, instead of the intended 15 minutes.</t>
	</section>


	<section anchor="conventions-and-definitions"><name>Conventions and Definitions<	</front>
	/name>
	<t>The key words "MUST", "MUST NOT", "REQUIRED", &
	quot;SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT&qu
	ot;, "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
	"OPTIONAL" in this document are to be interpreted as described in BCP
	14 <xref target="RFC2119"></xref> <xref target="RFC8174"></xref> when, and only
	when, they appear in all capitals, as shown here.</t>
	</section>


	<section anchor="nsec-and-nsec3-ttl-changes"><name>NSEC and NSEC3 TTL changes</n	<middle>
	ame>
	<t>The existing texts in <xref target="RFC4034"></xref>, <xref target="RFC4035">
	</xref>, and <xref target="RFC5155"></xref> use the SHOULD requirement level, bu
	t they were written when <xref target="RFC4035"></xref> still said 'However, it
	seems prudent for resolvers to avoid blocking new authoritative data or synthesi
	zing new data on their own'.
	<xref target="RFC8198"></xref> updated that text to contain 'DNSSEC-enabled vali
	dating resolvers SHOULD use wildcards and NSEC/NSEC3 resource records to generat
	e positive and negative responses until the effective TTLs or signatures for tho
	se records expire'.
	This means that correctness of NSEC and NSEC3 records, and their TTLs, has becom
	e much more important.
	Because of that, the updates in this document upgrade the requirement level to M
	UST.</t>


	<section anchor="updates-to-rfc4034"><name>Updates to RFC4034</name>	<section anchor="introduction"><name>Introduction</name>
	<t>Where <xref target="RFC4034"></xref> says:</t>	<t><xref target="RFC2308"></xref> defines the TTL of the Start of Authority (SO
	<blockquote><t>The NSEC RR SHOULD have the same TTL value as the SOA minimum TTL	A) record that must be returned in negative answers (NXDOMAIN or NODATA):</t>
	field. This is in the spirit of negative caching ([RFC2308]).</t>
		<blockquote><t>The TTL of this record is set from the minimum of the MINIMUM fi
		eld of the SOA record and the TTL of the SOA itself, and indicates how long a re
		solver may cache the negative answer.</t>
		</blockquote>

		<t>Thus, if the TTL of the SOA in the zone is lower than the SOA MINIMUM value
		(the last number in the SOA record),
		the authoritative server sends that lower value as the TTL of the returned SOA
		record.
		The resolver always uses the TTL of the returned SOA record when setting the ne
		gative TTL in its cache.</t>

		<t>However, <xref target="RFC4034" sectionFormat="comma" section="4"></xref> ha
		s this unfortunate text:</t>

		<blockquote><t>The NSEC RR <bcp14>SHOULD</bcp14> have the same TTL value as the
		SOA minimum TTL field. This is in the spirit of negative caching (<xref target=
		"RFC2308"/>).</t>
		</blockquote>

		<t>This text, while referring to <xref target="RFC2308"/>, can cause NSEC recor
		ds to have much higher TTLs than the appropriate negative TTL for a zone.
		<xref target="RFC5155"></xref> contains equivalent text.</t>

		<t><xref target="RFC8198" sectionFormat="comma" section="5.4"></xref> tries to
		correct this:</t>

		<blockquote><t><xref target="RFC2308" sectionFormat="of" section="5"/> also sta
		tes that a negative cache entry TTL is taken from the minimum of the SOA.MINIMUM
		field and SOA's TTL. This can be less than the TTL of an NSEC or NSEC3 record,
		since their TTL is equal to the SOA.MINIMUM field (see <xref target="RFC4035" s
		ectionFormat="comma" section="2.3"></xref> and <xref target="RFC5155" sectionFor
		mat="comma" section="3"/>).</t>

		<t>A resolver that supports aggressive use of NSEC and NSEC3 <bcp14>SHOULD</bcp
		14> reduce the TTL of NSEC and NSEC3 records to match the SOA.MINIMUM field in t
		he authority section of a negative response, if SOA.MINIMUM is smaller.</t>
		</blockquote>

		<t>But the NSEC and NSEC3 RRs should, according to <xref target="RFC4034"/> and
		<xref target="RFC5155"/>, already be at the value of the MINIMUM field in the
		SOA. Thus, the advice from <xref target="RFC8198"/> would not actually change t
		he TTL used for the NSEC and NSEC3 RRs for authoritative servers that follow the
		RFCs.</t>

		<t>As a theoretical exercise, consider a top-level domain (TLD) named .example w
		ith an SOA record like this:</t>

		<artwork name="" type="" align="left" alt=""><![CDATA[
		example. 900 IN SOA primary.example. dnsadmin.example. (
		1 1800 900 604800 86400 )
		]]></artwork>

		<t>The SOA record has a 900-second TTL and an 86400-second MINIMUM TTL.
		Negative responses from this zone have a 900-second TTL, but the NSEC or NSEC3
		records in those negative responses have an 86400-second TTL.
		If a resolver were to use those NSEC or NSEC3 records aggressively, they would
		be considered valid for a day instead of the intended 15 minutes.</t>
		</section>

		<section anchor="conventions-and-definitions"><name>Conventions and Definitions
		</name>
		<t>
		The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>", "<bcp14>REQ
		UIRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL
		NOT</bcp14>", "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>", "<bcp14
		>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
		"<bcp14>MAY</bcp14>", and "<bcp14>OPTIONAL</bcp14>" in this document are to
		be interpreted as
		described in BCP 14 <xref target="RFC2119"/> <xref target="RFC8174"/>
		when, and only when, they appear in all capitals, as shown here.
		</t>
		</section>

		<section anchor="nsec-and-nsec3-ttl-changes"><name>NSEC and NSEC3 TTL Changes</
		name>

		<t><xref target="RFC4034"></xref>, <xref target="RFC4035"></xref>, and <xref tar
		get="RFC5155"></xref> use the <bcp14>SHOULD</bcp14> requirement level, but they
		were written prior to the publication of <xref target="RFC8198"></xref> when <xr
		ef target="RFC4035"></xref> still said: </t>

		<blockquote><t>However, it seems prudent for resolvers to avoid blocking new aut
		horitative data or synthesizing new data on their own.</t></blockquote>
		<t>

		<xref target="RFC8198"></xref> updated that text to contain:</t> <blockquote><t>
		...DNSSEC-enabled validating resolvers <bcp14>SHOULD</bcp14> use wildcards and N
		SEC/NSEC3 resource records to generate positive and negative responses until the
		effective TTLs or signatures for those records expire.</t></blockquote><t>

		This means that the correctness of NSEC and NSEC3 records and their TTLs has bec
		ome much more important.

		Because of that, the updates in this document upgrade the requirement level to <
		bcp14>MUST</bcp14>.</t>

		<section anchor="updates-to-rfc4034"><name>Updates to RFC 4034</name>
		<t><xref target="RFC4034"></xref> says:</t>

		<blockquote><t>The NSEC RR <bcp14>SHOULD</bcp14> have the same TTL value as the
		SOA minimum TTL field. This is in the spirit of negative caching (<xref target=
		"RFC2308"/>).</t>
	</blockquote><t>This is updated to say:</t>	</blockquote><t>This is updated to say:</t>

	<blockquote><t>The TTL of the NSEC RR that is returned MUST be the lesser of the	<blockquote>
	MINIMUM field of the SOA record and the TTL of the SOA itself. This matches th
	e definition of the TTL for negative responses in <xref target="RFC2308"></xref>	<t>The TTL of the NSEC RR that is returned <bcp14>MUST</bcp14> be the lesser o
	. Because some signers incrementally update the NSEC chain, a transient inconsis	f the MINIMUM field of the SOA record and the TTL of the SOA itself. This match
	tency between the observed and expected TTL MAY exist.</t>	es the definition of the TTL for negative responses in <xref target="RFC2308"></
		xref>. Because some signers incrementally update the NSEC chain, a transient inc
		onsistency between the observed and expected TTL <bcp14>MAY</bcp14> exist.</t>
	</blockquote></section>	</blockquote></section>


	<section anchor="updates-to-rfc4035"><name>Updates to RFC4035</name>	<section anchor="updates-to-rfc4035"><name>Updates to RFC 4035</name>
	<t>Where <xref target="RFC4035"></xref> says:</t>	<t><xref target="RFC4035"></xref> says:</t>
	<blockquote><t>The TTL value for any NSEC RR SHOULD be the same as the minimum T
	TL value field in the zone SOA RR.</t>	<blockquote><t>The TTL value for any NSEC RR <bcp14>SHOULD</bcp14> be the same a
		s the minimum TTL value field in the zone SOA RR.</t>
	</blockquote><t>This is updated to say:</t>	</blockquote><t>This is updated to say:</t>

	<blockquote><t>The TTL of the NSEC RR that is returned MUST be the lesser of the	<blockquote>
	MINIMUM field of the SOA record and the TTL of the SOA itself. This matches th
	e definition of the TTL for negative responses in <xref target="RFC2308"></xref>	<t>The TTL of the NSEC RR that is returned <bcp14>MUST</bcp14> be the lesser o
	. Because some signers incrementally update the NSEC chain, a transient inconsis	f the MINIMUM field of the SOA record and the TTL of the SOA itself. This match
	tency between the observed and expected TTL MAY exist.</t>	es the definition of the TTL for negative responses in <xref target="RFC2308"></
		xref>. Because some signers incrementally update the NSEC chain, a transient inc
		onsistency between the observed and expected TTL <bcp14>MAY</bcp14> exist.</t>
	</blockquote></section>	</blockquote></section>


	<section anchor="updates-to-rfc5155"><name>Updates to RFC5155</name>	<section anchor="updates-to-rfc5155"><name>Updates to RFC 5155</name>
	<t>Where <xref target="RFC5155"></xref> says:</t>	<t><xref target="RFC5155"></xref> says:</t>
	<blockquote><t>The NSEC3 RR SHOULD have the same TTL value as the SOA minimum TT	<blockquote><t>The NSEC3 RR <bcp14>SHOULD</bcp14> have the same TTL value as the
	L field. This is in the spirit of negative caching [RFC2308].</t>	SOA minimum TTL field. This is in the spirit of negative caching <xref target=
		"RFC2308"/>.</t>
	</blockquote><t>This is updated to say:</t>	</blockquote><t>This is updated to say:</t>

	<blockquote><t>The TTL of the NSEC3 RR that is returned MUST be the lesser of th e MINIMUM field of the SOA record and the TTL of the SOA itself. This matches t he definition of the TTL for negative responses in <xref target="RFC2308"></xref >. Because some signers incrementally update the NSEC3 chain, a transient incons istency between the observed and expected TTL MAY exist.</t>	<blockquote><t>The TTL of the NSEC3 RR that is returned <bcp14>MUST</bcp14> be t he lesser of the MINIMUM field of the SOA record and the TTL of the SOA itself. This matches the definition of the TTL for negative responses in <xref target=" RFC2308"></xref>. Because some signers incrementally update the NSEC3 chain, a t ransient inconsistency between the observed and expected TTL <bcp14>MAY</bcp14> exist.</t>
	</blockquote><t>Where <xref target="RFC5155"></xref> says:</t>	</blockquote><t>Where <xref target="RFC5155"></xref> says:</t>

	<blockquote><t>o The TTL value for any NSEC3 RR SHOULD be the same as the minim	<blockquote>
	um TTL value field in the zone SOA RR.</t>	<ul empty="false">
	</blockquote><t>This is updated to say:</t>	<li>The TTL value for any NSEC3 RR <bcp14>SHOULD</bcp14> be the same as the mini
	<blockquote><t>o The TTL value for each NSEC3 RR MUST be the lesser of the MINI	mum TTL value field in the zone SOA RR.</li>
	MUM field of the zone SOA RR and the TTL of the zone SOA RR itself. Because some	</ul>
	signers incrementally update the NSEC3 chain, a transient inconsistency between	</blockquote>
	the observed and expected TTL MAY exist.</t>	<t>This is updated to say:</t>
		<blockquote>
		<ul empty="false">
		<li>The TTL value for each NSEC3 RR <bcp14>MUST</bcp14> be the lesser of the MIN
		IMUM field of the zone SOA RR and the TTL of the zone SOA RR itself. Because som
		e signers incrementally update the NSEC3 chain, a transient inconsistency betwee
		n the observed and expected TTL <bcp14>MAY</bcp14> exist.</li>
		</ul>
	</blockquote></section>	</blockquote></section>


	<section anchor="updates-to-rfc8198"><name>Updates to RFC8198</name>	<section anchor="updates-to-rfc8198"><name>Updates to RFC 8198</name>
	<t><xref target="RFC8198"></xref> section 5.4 (Consideration on TTL) is complete	<t><xref target="RFC8198" sectionFormat="comma" section="5.4"></xref> ("Consider
	ly replaced by the following text:</t>	ation on TTL") is completely replaced by the following text:</t>
	<blockquote><t>The TTL value of negative information is especially important,	<blockquote><t>The TTL value of negative information is especially important,
	because newly added domain names cannot be used while the negative	because newly added domain names cannot be used while the negative
	information is effective.</t>	information is effective.</t>

	<t>Section 5 of [RFC2308] suggests a maximum default negative cache TTL	<t><xref target="RFC2308" sectionFormat="of" section="5"/> suggests a maximum de
	value of 3 hours (10800). It is RECOMMENDED that validating	fault negative cache TTL
		value of 3 hours (10800). It is <bcp14>RECOMMENDED</bcp14> that validating
	resolvers limit the maximum effective TTL value of negative responses	resolvers limit the maximum effective TTL value of negative responses
	(NSEC/NSEC3 RRs) to this same value.</t>	(NSEC/NSEC3 RRs) to this same value.</t>

	<t>A resolver that supports aggressive use of NSEC and NSEC3 MAY	<t>A resolver that supports aggressive use of NSEC and NSEC3 <bcp14>MAY</bcp14>
	limit the TTL of NSEC and NSEC3 records to the lesser of the SOA.MINIMUM	limit the TTL of NSEC and NSEC3 records to the lesser of the SOA.MINIMUM
	field and the TTL of the SOA in a response, if present.	field and the TTL of the SOA in a response, if present.

	It MAY also use a previously cached SOA for a zone to find these values.</t>	It <bcp14>MAY</bcp14> also use a previously cached SOA for a zone to find the se values.</t>
	</blockquote><t>(The third paragraph of the original is removed, and the fourth paragraph is updated to allow resolvers to also take the lesser of the SOA TTL a nd SOA MINIMUM.)</t>	</blockquote><t>(The third paragraph of the original is removed, and the fourth paragraph is updated to allow resolvers to also take the lesser of the SOA TTL a nd SOA MINIMUM.)</t>
	</section>	</section>
	</section>	</section>

	<section anchor="zone-operator-considerations"><name>Zone Operator Consideration s</name>	<section anchor="zone-operator-considerations"><name>Zone Operator Consideration s</name>
	<t>If signers and DNS servers for a zone cannot immediately be updated to confor m to this document, zone operators are encouraged to consider setting their SOA record TTL and the SOA MINIMUM field to the same value.	<t>If signers and DNS servers for a zone cannot immediately be updated to confor m to this document, zone operators are encouraged to consider setting their SOA record TTL and the SOA MINIMUM field to the same value.
	That way, the TTL used for aggressive NSEC and NSEC3 use matches the SOA TTL for negative responses.</t>	That way, the TTL used for aggressive NSEC and NSEC3 use matches the SOA TTL for negative responses.</t>
	<t>Note that some signers might use the SOA TTL or MINIMUM as a default for othe r values, such as the TTL for DNSKEY records.	<t>Note that some signers might use the SOA TTL or MINIMUM as a default for othe r values, such as the TTL for DNSKEY records.
	Operators should consult documentation before changing values.</t>	Operators should consult documentation before changing values.</t>


	<section anchor="a-note-on-wildcards"><name>A Note On Wildcards</name>	<section anchor="a-note-on-wildcards"><name>A Note on Wildcards</name>
	<t>Validating resolvers consider an expanded wildcard valid for the wildcard's T TL, capped by the TTLs of the NSEC or NSEC3 proof that shows that the wildcard e xpansion is legal.	<t>Validating resolvers consider an expanded wildcard valid for the wildcard's T TL, capped by the TTLs of the NSEC or NSEC3 proof that shows that the wildcard e xpansion is legal.

	Thus, changing the TTL of NSEC or NSEC3 records (explicitly, or by implementatio n of this document, implicitly) might affect (shorten) the lifetime of wildcards .</t>	Thus, changing the TTL of NSEC or NSEC3 records (explicitly, or by implementatio n of this document implicitly) might affect (shorten) the lifetime of wildcards. </t>
	</section>	</section>
	</section>	</section>

	<section anchor="security-considerations"><name>Security Considerations</name>	<section anchor="security-considerations"><name>Security Considerations</name>
	<t>An attacker can delay future records from appearing in a cache by seeding the cache with queries that cause NSEC or NSEC3 responses to be cached for aggressi ve use purposes.	<t>An attacker can delay future records from appearing in a cache by seeding the cache with queries that cause NSEC or NSEC3 responses to be cached for aggressi ve use purposes.
	This document reduces the impact of that attack in cases where the NSEC or NSEC3 TTL is higher than the zone operator intended.</t>	This document reduces the impact of that attack in cases where the NSEC or NSEC3 TTL is higher than the zone operator intended.</t>
	</section>	</section>

	<section anchor="iana-considerations"><name>IANA Considerations</name>	<section anchor="iana-considerations"><name>IANA Considerations</name>

	<t>IANA is requested to add a reference to this document in the "Resource R ecord (RR) TYPEs" subregistry of the "Domain Name System (DNS) Paramet ers" registry, for the NSEC and NSEC3 types.</t>	<t>IANA has added a reference to this document in the "Resource Record (RR) TYPEs" subregistry of the "Domain Name System (DNS) Parameters" registry for the NSEC and NSEC3 types.</t>
	</section>	</section>

	</middle>	</middle>

	<back>	<back>
	<references><name>Normative References</name>	<references><name>Normative References</name>
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8174. xml"/>	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8174. xml"/>
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2308. xml"/>	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2308. xml"/>
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4034. xml"/>	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4034. xml"/>
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5155. xml"/>	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5155. xml"/>
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8198. xml"/>	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8198. xml"/>
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4035. xml"/>	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4035. xml"/>
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2119. xml"/>	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2119. xml"/>
	</references>	</references>


	<section anchor="implementation-status"><name>Implementation Status</name>
	<t>[RFC Editor: please remove this section before publication]</t>
	<t>Implemented in PowerDNS Authoritative Server 4.3.0 <eref target="https://doc.
	powerdns.com/authoritative/dnssec/operational.html?highlight=ttl#some-notes-on-t
	tl-usage">https://doc.powerdns.com/authoritative/dnssec/operational.html?highlig
	ht=ttl#some-notes-on-ttl-usage</eref> .</t>
	<t>Implemented in BIND 9.16 and up, to be released early 2021 <eref target="http
	s://mailarchive.ietf.org/arch/msg/dnsop/ga41J2PPUbmc21--dqf3i7_IY6M">https://mai
	larchive.ietf.org/arch/msg/dnsop/ga41J2PPUbmc21--dqf3i7_IY6M</eref> <eref target
	="https://gitlab.isc.org/isc-projects/bind9/-/merge_requests/4506">https://gitla
	b.isc.org/isc-projects/bind9/-/merge_requests/4506</eref> .</t>
	<t>Implemented in Knot DNS 3.1, to be released in 2021 <eref target="https://git
	lab.nic.cz/knot/knot-dns/-/merge_requests/1219">https://gitlab.nic.cz/knot/knot-
	dns/-/merge_requests/1219</eref> .</t>
	<t>Implemented in ldns, patch under review <eref target="https://github.com/NLne
	tLabs/ldns/pull/118">https://github.com/NLnetLabs/ldns/pull/118</eref></t>
	<t>Implementation status is tracked at <eref target="https://trac.ietf.org/trac/
	dnsop/wiki/draft-ietf-dnsop-nsec-ttl">https://trac.ietf.org/trac/dnsop/wiki/draf
	t-ietf-dnsop-nsec-ttl</eref></t>
	</section>

	<section anchor="document-history"><name>Document history</name>
	<t>[RFC editor: please remove this section before publication.]</t>
	<t>From draft-vandijk-dnsop-nsec-ttl-00 to draft-ietf-dnsop-nsec-ttl-00:</t>

	<ul>
	<li>document was adopted</li>
	<li>various minor editorial changes</li>
	<li>now also updates 4035</li>
	<li>use .example instead of .com for the example</li>
	<li>more words on 8198</li>
	<li>a note on wildcards</li>
	</ul>
	<t>From draft-ietf-dnsop-nsec-ttl-00 to draft-ietf-dnsop-nsec-ttl-01:</t>

	<ul>
	<li>various wording improvements</li>
	<li>added Implementation note from Knot, expanded the BIND one with the GitLab M
	R URL</li>
	<li>reduced requirement level from MUST to SHOULD, like the original texts</li>
	</ul>
	<t>From draft-ietf-dnsop-nsec-ttl-01 to draft-ietf-dnsop-nsec-ttl-02:</t>

	<ul>
	<li>updated the second bit of wrong text in 5155</li>
	</ul>
	<t>From draft-ietf-dnsop-nsec-ttl-02 to draft-ietf-dnsop-nsec-ttl-03:</t>

	<ul>
	<li>document now updates resolver behaviour in 8198</li>
	<li>lots of extra text to clarify what behaviour goes where (thanks Paul Hoffman
	)</li>
	<li>replace 'any' with 'each' (thanks Duane)</li>
	<li>upgraded requirement level to MUST, plus a note on incremental signers</li>
	</ul>
	<t>From draft-ietf-dnsop-nsec-ttl-03 to draft-ietf-dnsop-nsec-ttl-04:</t>

	<ul>
	<li>the 'incremental signer exception' is now part of all relevant document upda
	tes</li>
	<li>added an explanation for the upgraded requirement level</li>
	</ul>
	<t>From draft-ietf-dnsop-nsec-ttl-04 to draft-ietf-dnsop-nsec-ttl-05:</t>

	<ul>
	<li>various minor rewordings (from IESG review, and things I spotted while handl
	ing IESG review comments)</li>
	<li>added a note on the secondary impact of changing the SOA TTL and/or MINIMUM
	(IESG review)</li>
	</ul>
	</section>

	<section anchor="acknowledgements" numbered="false"><name>Acknowledgements</name >	<section anchor="acknowledgements" numbered="false"><name>Acknowledgements</name >
	<t>This document was made possible with the help of the following people:</t>	<t>This document was made possible with the help of the following people:</t>


	<ul>	<ul spacing="normal">
	<li>Ralph Dolmans</li>	<li><t><contact fullname="Ralph Dolmans"/></t></li>
	<li>Warren Kumari</li>	<li><t><contact fullname="Warren Kumari"/></t></li>
	<li>Matthijs Mekking</li>	<li><t><contact fullname="Matthijs Mekking"/></t></li>
	<li>Vladimir Cunat</li>	<li><t><contact fullname="Vladimir Cunat"/></t></li>
	<li>Matt Nordhoff</li>	<li><t><contact fullname="Matt Nordhoff"/></t></li>
	<li>Josh Soref</li>	<li><t><contact fullname="Josh Soref"/></t></li>
	<li>Tim Wicinski</li>	<li><t><contact fullname="Tim Wicinski"/></t></li>
	</ul>	</ul>

	<t>The author would like to explicitly thank Paul Hoffman for extensive reviews, text contributions, and help in navigating WG comments.</t>	<t>The author would like to explicitly thank <contact fullname="Paul Hoffman"/> for the extensive reviews, text contributions, and help in navigating WG comment s.</t>
	</section>	</section>

	</back>	</back>

	</rfc>	</rfc>

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