rfc8801xml2.original.xml   rfc8801.xml 
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE rfc SYSTEM "rfc2629-xhtml.ent">
<rfc xmlns:xi="http://www.w3.org/2001/XInclude" ipr="trust200902"
docName="draft-ietf-intarea-provisioning-domains-11" number="8801"
submissionType="IETF" category="std" consensus="true" obsoletes=""
updates="" xml:lang="en" tocInclude="true" sortRefs="true" symRefs="true"
version="3">
<front>
<title abbrev="Provisioning Domains">Discovering Provisioning Domain Names
and Data</title>
<seriesInfo name="RFC" value="8801"/>
<author initials="P." surname="Pfister" fullname="Pierre Pfister">
<organization>Cisco</organization>
<address>
<postal>
<street>11 Rue Camille Desmoulins</street>
<city>Issy-les-Moulineaux</city><code>92130</code>
<country>France</country>
</postal>
<email>ppfister@cisco.com</email>
</address>
</author>
<author initials="É." surname="Vyncke" fullname="Éric Vyncke">
<organization>Cisco</organization>
<address>
<postal>
<street>De Kleetlaan, 6</street>
<city>Diegem</city><code>1831</code>
<country>Belgium</country>
</postal>
<email>evyncke@cisco.com</email>
</address>
</author>
<author initials="T." surname="Pauly" fullname="Tommy Pauly">
<organization>Apple Inc.</organization>
<address>
<postal>
<street>One Apple Park Way</street>
<city>Cupertino</city><region>California</region><code>95014</code>
<country>United States of America</country>
</postal>
<email>tpauly@apple.com</email>
</address>
</author>
<author initials="D." surname="Schinazi" fullname="David Schinazi">
<organization>Google LLC</organization>
<address>
<postal>
<street>1600 Amphitheatre Parkway</street>
<city>Mountain
View</city><region>California</region><code>94043</code>
<country>United States of America</country>
</postal>
<email>dschinazi.ietf@gmail.com</email>
</address>
</author>
<author initials="W." surname="Shao" fullname="Wenqin Shao">
<organization>Cisco</organization>
<address>
<postal>
<street>11 Rue Camille Desmoulins</street>
<city>Issy-les-Moulineaux</city><code>92130</code>
<country>France</country>
</postal>
<email>wenshao@cisco.com</email>
</address>
</author>
<date year="2020" month="July"/>
<keyword>IPv6</keyword>
<keyword>Provisioning</keyword>
<keyword>DHCP</keyword>
<keyword>PvD</keyword>
<abstract>
<t>Provisioning Domains (PvDs) are defined as consistent
sets of network configuration information. PvDs allows hosts to manage
connections to multiple networks and interfaces simultaneously, such as
when a home router provides connectivity through both a broadband and
cellular network provider.</t>
<t>This document defines a mechanism for explicitly identifying PvDs
through
a Router Advertisement (RA) option. This RA option announces a PvD identifier,
which hosts can compare to differentiate between PvDs. The option can directly
carry some information about a PvD and can optionally point to
PvD Additional Information that can be retrieved using HTTP over TLS.</t>
</abstract>
</front>
<middle>
<section anchor="introduction" numbered="true" toc="default">
<name>Introduction</name>
<t>Provisioning Domains (PvDs) are defined in <xref target="RFC7556"
format="default"/> as consistent
sets of network configuration information. This information includes
properties that are traditionally associated with a single networking
interface, such as source addresses, DNS configuration, proxy configuration,
and gateway addresses.</t>
<t>Clients that are aware of PvDs can take advantage of multiple network
interfaces simultaneously. This enables using two PvDs in parallel for
separate connections or for multi-path transports.</t>
<t>While most PvDs today are discovered implicitly (such as by receiving
information via Router Advertisements from a router on a network
that a client host directly connects to), <xref target="RFC7556"
format="default"/> also defines the notion
of Explicit PvDs. IPsec Virtual Private Networks are considered Explicit PvDs,
but Explicit PvDs can also be discovered via the local network router.
Discovering Explicit PvDs allows two key advancements in managing multiple
PvDs:</t>
<ol spacing="normal" type="1">
<li>The ability to discover and use multiple PvDs on a single
interface,
such as when a local router can provide connectivity to two different
Internet Service Providers.</li>
<li>The ability to associate Additional Information about PvDs to
describe
the properties of the network.</li>
</ol>
<t>While <xref target="RFC7556" format="default"/> defines the concept
of Explicit PvDs, it does not define
the mechanism for discovering multiple Explicit PvDs on a single network
and their Additional Information.</t>
<t>This document specifies a way to identify PvDs with Fully Qualified
Domain Names (FQDNs), called PvD IDs. Those identifiers are advertised in
a new Router Advertisement (RA) <xref target="RFC4861" format="default"/>
option called
the PvD Option, which, when present, associates
the PvD ID with all the information present in the Router Advertisement
as well as any configuration object, such as addresses, derived from
it. The PvD Option may also contain a set of
other RA options, along with an optional inner Router Advertisement
message header. These options and optional inner header are only visible
to 'PvD-aware' hosts, allowing such hosts to have a specialized view of the
network configuration.</t>
<t>Since PvD IDs are used to identify different ways to access the
Internet, multiple PvDs (with different PvD IDs) can be provisioned on
a single host interface. Similarly, the same PvD ID could be used on
different interfaces of a host in order to inform that those PvDs
ultimately provide equivalent services.</t>
<t>This document also introduces a mechanism for hosts to retrieve
optional Additional Information related to a specific PvD by means of an
HTTP-over-TLS query using a URI derived from the PvD ID. The retrieved
JSON object contains Additional Information that would typically be
considered too large to be directly included in the Router
Advertisement but might be considered useful to the applications, or
even sometimes users, when choosing which PvD should be used.</t>
<t>For example, if Alice has both a cellular network provider and a
broadband provider in her home, her PvD-aware devices and applications
would be aware of both available uplinks. These applications
could fail-over between these networks or run connections over both
(potentially using multi-path transports). Applications could also select
specific uplinks based on the properties of the network; for example,
if the cellular network provides free high-quality video streaming,
a video-streaming application could select that network while most of the
other traffic on Alice's device uses the broadband provider.</t>
<section anchor="specification-of-requirements" numbered="true"
toc="default">
<name>Specification of Requirements</name>
<t>
The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>",
"<bcp14>REQUIRED</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&nbsp;14 <xref target="RFC2119"/> <xref target="RFC8174"/>
when, and only when, they appear in all capitals, as shown here.
</t>
</section>
</section>
<section anchor="terminology" numbered="true" toc="default">
<name>Terminology</name>
<t>This document uses the following terminology:</t>
<dl newline="false" spacing="normal">
<dt>Provisioning Domain (PvD):</dt>
<dd>
A set of network configuration information; for more information, see <xref
target="RFC7556" format="default"/>.</dd>
<dt>PvD ID:</dt>
<dd>
A Fully Qualified Domain Name (FQDN) used to identify a PvD.</dd>
<dt>Explicit PvD:</dt>
<dd>
A PvD uniquely identified with a PvD ID. For more information, see <xref
target="RFC7556" format="default"/>.</dd>
<dt>Implicit PvD:</dt>
<dd>
A PvD that, in the absence of a PvD ID,
is identified by the host interface to which it is attached and the
address of the advertising router. See also <xref target="RFC7556"
format="default"/>.</dd>
<dt>PvD-aware host:</dt>
<dd>
A host that supports the association of
network configuration information into PvDs and the use of these
PvDs as described in this document. Also named "PvD-aware node" in <xref
target="RFC7556" format="default"/>.</dd>
</dl>
</section>
<section anchor="ra" numbered="true" toc="default">
<name>Provisioning Domain Identification Using Router
Advertisements</name>
<t>Explicit PvDs are identified by a PvD ID. The PvD ID is a Fully
Qualified Domain Name (FQDN) that identifies the network operator.
Network operators <bcp14>MUST</bcp14> use names that they own or manage to
avoid naming conflicts. The same PvD ID <bcp14>MAY</bcp14> be used in
several access networks when they ultimately provide identical services
(e.g., in all home networks subscribed to the same service); else, the
PvD ID <bcp14>MUST</bcp14> be different to follow <xref
target="RFC7556" sectionFormat="of" section="2.4"/>.</t>
<section anchor="pvd-id-option-for-router-advertisements"
numbered="true" toc="default">
<name>PvD Option for Router Advertisements</name>
<t>This document introduces a Router Advertisement (RA) option called
the PvD Option. It is used to convey the FQDN identifying a given PvD (see
<xref target="format" format="default"/>), bind the PvD ID with configuration
information received over DHCPv4 (see <xref target="dhcpv4"
format="default"/>), enable
the use of HTTP over TLS to retrieve the PvD Additional Information
JSON object (see <xref target="data" format="default"/>), as well as contain
any other
RA options that would otherwise be valid in the RA.</t>
<figure anchor="format">
<name>PvD Option Format</name>
<artwork name="" type="" align="left" alt=""><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |H|L|R| Reserved | Delay |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number | ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
... PvD ID FQDN ...
... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
... | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ...
... Router Advertisement message header ...
... (Only present when R-flag is set) ...
... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
]]></artwork>
</figure>
<dl newline="false" spacing="normal">
<dt>Type:</dt>
<dd>
(8 bits) Set to 21.</dd>
<dt>Length:</dt>
<dd>
(8 bits) The length of the option in
units of 8 octets, including the Type and Length fields, the
Router Advertisement message header, if any, as well as the RA
options that are included within the PvD Option.</dd>
<dt>H-flag:</dt>
<dd>
(1 bit) 'HTTP' flag stating whether some PvD Additional Information is made
available through HTTP over TLS, as described in <xref target="data"
format="default"/>.</dd>
<dt>L-flag:</dt>
<dd>
(1 bit) 'Legacy' flag stating whether the PvD is associated with
IPv4 information assigned using DHCPv4 (see <xref target="dhcpv4"
format="default"/>).</dd>
<dt>R-flag:</dt>
<dd>
(1 bit) 'Router Advertisement' flag stating whether the PvD Option header is
followed (right after padding to the next 64-bit boundary) by a Router
Advertisement message header (see <xref target="RFC4861"
sectionFormat="of" section="4.2"/>). The usage of the inner message header
is described in
<xref target="host" format="default"/>.</dd>
<dt>Reserved:</dt>
<dd>
(9 bits) Reserved for later use. It
<bcp14>MUST</bcp14> be set to zero by the sender and ignored by the
receiver.</dd>
<dt>Delay:</dt>
<dd>
(4 bits) Unsigned integer used to delay HTTP GET queries from hosts by a
randomized backoff (see <xref target="retr" format="default"/>). If the
H-flag is not set, senders <bcp14>SHOULD</bcp14> set the delay to zero, and
receivers <bcp14>SHOULD</bcp14> ignore the value.</dd>
<dt>Sequence Number:</dt>
<dd>
(16 bits) Sequence number for the PvD Additional Information, as described
in
<xref target="data" format="default"/>. If the H-flag is not set, senders
<bcp14>SHOULD</bcp14> set the Sequence Number to zero, and receivers
<bcp14>SHOULD</bcp14> ignore the value.</dd>
<dt>PvD ID FQDN:</dt>
<dd>
The FQDN used as PvD ID encoded in DNS format, as described in <xref
target="RFC1035" sectionFormat="of" section="3.1"/>. Domain name compression
as described in <xref target="RFC1035" sectionFormat="of" section="4.1.4"/>
<bcp14>MUST NOT</bcp14> be used.</dd>
<dt>Padding:</dt>
<dd>
Zero or more padding octets to the next 8-octet boundary (see <xref
target="RFC4861" sectionFormat="of" section="4.6"/>). It <bcp14>MUST</bcp14>
be set to zero by the sender and ignored by the receiver.</dd>
<dt>RA message header:</dt>
<dd>
(16 octets) When the R-flag is set, a full Router Advertisement message
header as specified in <xref target="RFC4861" format="default"/>. The sender
<bcp14>MUST</bcp14> set the Type field to 134 (the value for "Router
Advertisement") and set the Code field to 0. Receivers <bcp14>MUST</bcp14>
ignore both of these fields. The Checksum field <bcp14>MUST</bcp14> be set
to 0
by the sender; non-zero checksums <bcp14>MUST</bcp14> be ignored by the
receiver without causing the processing of the message to fail. All other
fields are to be set and parsed as specified in <xref target="RFC4861"
format="default"/> or any updating documents.</dd>
<dt>Options:</dt>
<dd>
Zero or more RA options that would otherwise be valid as part of the Router
Advertisement main body but are instead included in the PvD Option so as to
be ignored by hosts that are not PvD aware.</dd>
</dl>
<t><xref target="pvd_example" format="default"/> shows an example of a
PvD Option with "example.org" as the PvD ID FQDN and includes both a
Recursive DNS Server (RDNSS) option and a Prefix Information
Option. It has a Sequence Number of 123 and indicates the presence of
PvD Additional Information that is expected to be fetched with a delay
factor of 1.</t>
<figure anchor="pvd_example">
<name>Example PvD Option</name>
<artwork name="" type="" align="left" alt=""><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+-----------------------------------------------+
| Type: 21 | Length: 12 |1|0|0| Reserved |Delay:1|
+---------------+-------------------------------+---------------+
| Seq number: 123 | 7 | e |
+---------------+-----------------------------------------------+
| x | a | m | p |
+---------------------------------------------------------------+
| l | e | 3 | o |
+---------------------------------------------------------------+
| r | g | 0 | 0 (padding) |
+---------------------------------------------------------------+
| 0 (padding) | 0 (padding) | 0 (padding) | 0 (padding) |
+---------------+---------------+---------------+---------------+
| RDNSS option (RFC 8106) length: 5 ...
... ...
... |
+---------------------------------------------------------------+
| Prefix Information Option (RFC 4861) length: 4 ...
... |
... |
+---------------------------------------------------------------+
]]></artwork>
</figure>
</section>
<section anchor="router" numbered="true" toc="default">
<name>Router Behavior</name>
<t>A router <bcp14>MAY</bcp14> send RAs containing one PvD Option but
<bcp14>MUST NOT</bcp14> include more than one PvD Option in each
RA. The PvD Option <bcp14>MUST NOT</bcp14> contain further PvD
Options.</t>
<t>The PvD Option <bcp14>MAY</bcp14> contain zero, one, or more RA
options that would otherwise be valid as part of the same RA. Such
options are processed by PvD-aware hosts and ignored by other hosts as
per <xref sectionFormat="of" section="4.2"
target="RFC4861"/>.</t>
<t>In order to provide multiple different PvDs, a router
<bcp14>MUST</bcp14> send multiple RAs. RAs sent from different
link-local source addresses establish distinct Implicit PvDs in the
absence of a PvD Option. Explicit PvDs <bcp14>MAY</bcp14> share
link-local source addresses with an Implicit PvD and any number of
other Explicit PvDs.</t>
<t>In other words, different Explicit PvDs <bcp14>MAY</bcp14> be
advertised with RAs using the same link-local source address, but
different Implicit PvDs, advertised by different RAs,
<bcp14>MUST</bcp14> use different link-local addresses because these
Implicit PvDs are identified by the source addresses of the RAs. If a
link-local address on the router is changed, then any new RA will be
interpreted as a different Implicit PvD by PvD-aware hosts.</t>
<t>As specified in <xref target="RFC4861" format="default"/> and <xref
target="RFC6980" format="default"/>, when the set of options causes
the size of an advertisement to exceed the link MTU, multiple router
advertisements <bcp14>MUST</bcp14> be sent to avoid fragmentation,
each containing a subset of the options. In such cases, the PvD Option
header (i.e., all fields except the Options field)
<bcp14>MUST</bcp14> be repeated in all the transmitted RAs.
The options within the Options field <bcp14>MAY</bcp14> be transmitted only
once, included in one of the transmitted PvD Options.</t>
</section>
<section anchor="non-pvd-aware-host-behavior" numbered="true"
toc="default">
<name>Non-PvD-Aware Host Behavior</name>
<t>As the PvD Option has a new option code, non-PvD-aware hosts will
simply ignore the PvD Option and all the options it contains (see
<xref target="RFC4861" sectionFormat="of" section="4.2"/>). This
ensures the backward compatibility required in <xref target="RFC7556"
sectionFormat="of" section="3.3"/>. This behavior allows for a
mixed-mode network where a mix of PvD-aware and non-PvD-aware hosts
coexist.</t>
</section>
<section anchor="host" numbered="true" toc="default">
<name>PvD-Aware Host Behavior</name>
<t>Hosts <bcp14>MUST</bcp14> associate received RAs and included
configuration information (e.g., Router Valid Lifetime, Prefix
Information <xref target="RFC4861" format="default"/>, Recursive DNS
Server <xref target="RFC8106" format="default"/>, and Routing
Information
<xref target="RFC4191" format="default"/> options) with the Explicit
PvD identified by the first PvD Option present in the received RA, if
any, or with the Implicit PvD identified by the host interface and the
source address of the received RA otherwise. If an RA message header
is present both within the PvD Option and outside it, the header
within the PvD Option takes precedence.</t>
<t>In case multiple PvD Options are found in a given RA, hosts
<bcp14>MUST</bcp14> ignore all but the first PvD Option.</t>
<t>If a host receives PvD Options flags that it does not recognize
(currently in the Reserved field), it <bcp14>MUST</bcp14> ignore these
flags.</t>
<t>Similarly, hosts <bcp14>MUST</bcp14> associate all network
configuration objects (e.g., default routers, addresses, more specific
routes, and DNS Recursive Resolvers) with the PvD associated with the
RA that provisioned the object. For example, addresses that are
generated using a received Prefix Information Option (PIO) are
associated with the PvD of the last received RA that included the
given PIO.</t>
<t>PvD IDs <bcp14>MUST</bcp14> be compared in a case-insensitive
manner as defined by
<xref target="RFC4343" format="default"/>. For example, "pvd.example.com." or
"PvD.Example.coM."
would refer to the same PvD.</t>
<t>While performing PvD-specific operations such as resolving names,
executing the default address selection algorithm <xref
target="RFC6724" format="default"/>, or executing the default router
selection algorithm when forwarding packets <xref target="RFC4861"
format="default"/> <xref target="RFC4191" format="default"/>
<xref target="RFC8028" format="default"/>, hosts and applications
<bcp14>MAY</bcp14> consider only the configuration associated with any
non-empty subset of PvDs. For example, a host <bcp14>MAY</bcp14>
associate a given process with a specific PvD, or a specific set of
PvDs, while associating another process with another PvD. A PvD-aware
application might also be able to select, on a per-connection basis,
which PvDs should be used. In particular, constrained devices such as
small battery-operated devices (e.g., Internet of Things (IoT)) or
devices with limited
CPU or memory resources may purposefully use a single PvD while
ignoring some received RAs containing different PvD IDs.</t>
<t>The way an application expresses its desire to use a given PvD, or
a set of PvDs, and the way this selection is enforced are out of the
scope of this document. Useful insights about these considerations can
be found in <xref target="I-D.kline-mif-mpvd-api-reqs"
format="default"/>.</t>
<section anchor="dhcpv6" numbered="true" toc="default">
<name>DHCPv6 Configuration Association</name>
<t>When a host retrieves stateless configuration elements using
DHCPv6 (e.g., DNS recursive resolvers or DNS domain search lists
<xref target="RFC3646" format="default"/>), they <bcp14>MUST</bcp14>
be associated with all the Explicit and Implicit PvDs received on
the same interface and contained in an RA with the O-flag set <xref
target="RFC4861" format="default"/>.</t>
<t>When a host retrieves stateful assignments using DHCPv6, such
assignments <bcp14>MUST</bcp14> be associated with the received PvD that was
received with RAs with the M-flag set and including a matching PIO.
A PIO is considered to match a DHCPv6 assignment when the IPv6 prefix
from the PIO includes the assignment from DHCPv6. For example,
if a PvD's associated PIO defines the prefix <tt>2001:db8:cafe::/64</tt>,
a DHCPv6 IA_NA message that assigns the address
<tt>2001:db8:cafe::1234:4567</tt>
would be considered to match.</t>
<t>In cases where an address would be assigned by DHCPv6 and no
matching
PvD could be found, hosts <bcp14>MAY</bcp14> associate the assigned address
with any
Implicit PvD received on the same interface or to multiple Implicit PvDs
received on the same interface. This is intended to resolve
backward-compatibility
issues with rare deployments choosing to assign addresses with DHCPv6 while
not sending any matching PIO. Implementations are suggested to flag or log
such scenarios as errors to help detect misconfigurations.</t>
</section>
<section anchor="dhcpv4" numbered="true" toc="default">
<name>DHCPv4 Configuration Association</name>
<t>Associating DHCPv4 <xref target="RFC2131" format="default"/>
configuration elements with Explicit PvDs allows hosts to treat a
set of IPv4 and IPv6 configurations as a single PvD with shared
properties. For example, consider a router that provides two
different uplinks. One could be a broadband network that has data
rate and streaming properties described in PvD Additional
Information and that provides both IPv4 and IPv6 network access. The
other could be a cellular network that provides only IPv6 network
access and uses NAT64 <xref target="RFC6146" format="default"/>. The
broadband network can be represented by an Explicit PvD that points
to the Additional Information and also marks association with DHCPv4
information. The cellular network can be represented by a different
Explicit PvD that is not associated with DHCPv4.</t>
<t>When a PvD-aware host retrieves configuration elements from
DHCPv4, the information is associated either with a single Explicit
PvD on that interface or else with all Implicit PvDs on the same
interface.</t>
<t>An Explicit PvD indicates its association with DHCPv4 information
by setting the L-flag in the PvD Option. If there is exactly one
Explicit PvD that sets this flag, hosts <bcp14>MUST</bcp14>
associate the DHCPv4 information with that PvD. Multiple Explicit
PvDs on the same interface marking this flag is a misconfiguration,
and hosts <bcp14>SHOULD NOT</bcp14> associate the DHCPv4 information
with any Explicit PvD in this case.</t>
<t>If no single Explicit PvD claims association with DHCPv4, the
configuration elements coming from DHCPv4 <bcp14>MUST</bcp14> be
associated with all Implicit PvDs identified by the interface on
which the DHCPv4 transaction happened. This maintains existing host
behavior.</t>
</section>
<section anchor="connection-sharing-by-the-host" numbered="true"
toc="default">
<name>Connection Sharing by the Host</name>
<t>The situation in which a host shares connectivity from an
upstream interface (e.g., cellular) to a downstream interface (e.g.,
Wi-Fi) is known as 'tethering'. Techniques such as ND Proxy <xref
target="RFC4389" format="default"/>, 64share <xref target="RFC7278"
format="default"/>, or prefix delegation (e.g., using DHCPv6-PD
<xref target="RFC8415" format="default"/>) may be used for that
purpose.</t>
<t>Whenever the RAs received from the upstream interface contain a
PvD Option, hosts that are sharing connectivity
<bcp14>SHOULD</bcp14> include a PvD Option within the RAs sent
downstream with:</t>
<ul spacing="normal">
<li>The same PvD ID FQDN</li>
<li>The same H-flag, Delay, and Sequence Number values</li>
<li>The L-flag set whenever the host is sharing IPv4 connectivity
received from the same upstream interface</li>
<li>The bits in the Reserved field set to 0</li>
</ul>
<t>The values of the R-flag, Router Advertisement message
header, and Options field depend on whether or not the connectivity should
be shared only with PvD-aware hosts (see <xref target="router"
format="default"/>). In particular,
all options received within the upstream PvD Option and included in
the downstream RA <bcp14>SHOULD</bcp14> be included in the downstream PvD
Option.</t>
</section>
<section anchor="usage-of-dns-servers" numbered="true" toc="default">
<name>Usage of DNS Servers</name>
<t>PvD-aware hosts can be provisioned with recursive DNS servers via
RA options passed within an Explicit PvD, via RA options associated
with an Implicit PvD, via DHCPv6 or DHCPv4, or from some other
provisioning mechanism that creates an Explicit PvD (such as a VPN).
In all of these cases, the recursive DNS server addresses
<bcp14>SHOULD</bcp14> be
associated with the corresponding PvD. Specifically, queries sent
to a configured recursive DNS server <bcp14>SHOULD</bcp14> be sent from a
local IP
address that was provisioned for the PvD via RA or DHCP. Answers
received from the DNS server <bcp14>SHOULD</bcp14> only be used on the same
PvD.</t>
<t>PvD-aware applications will be able to select which PvD(s) to use
for DNS resolution and connections, which allows them to effectively
use multiple Explicit PvDs. In order to support non-PvD-aware
applications, however, PvD-aware hosts <bcp14>SHOULD</bcp14> ensure
that non-PvD-aware name resolution APIs like "getaddrinfo" only use
resolvers from a single PvD for a given query. Handling DNS across
PvDs is discussed in <xref sectionFormat="of" section="5.2.1"
target="RFC7556"/>, and PvD APIs are discussed in <xref
sectionFormat="of" section="6" target="RFC7556"
format="default"/>.</t>
<t>Maintaining the correct usage of DNS within PvDs avoids various
practical errors such as:</t>
<ul spacing="normal">
<li>A PvD associated with a VPN or otherwise private network may
provide DNS answers that contain addresses inaccessible over
another PvD. This includes the DNS queries to retrieve PvD
Additional Information, which could otherwise send identifying
information to the recursive DNS system (see <xref target="retr"
format="default"/>).</li>
<li>A PvD that uses a NAT64 <xref target="RFC6146"
format="default"/> and DNS64
<xref target="RFC6147" format="default"/> will synthesize IPv6 addresses in
DNS
answers that are not globally routable and would be invalid on
other PvDs. Conversely, an IPv4 address resolved via DNS on
another PvD cannot be directly used on a NAT64 network.</li>
</ul>
</section>
</section>
</section>
<section anchor="data" numbered="true" toc="default">
<name>Provisioning Domain Additional Information</name>
<t>Additional information about the network characteristics can be
retrieved based on the PvD ID. This set of information is called PvD
Additional Information and is encoded as a JSON object <xref
target="RFC8259" format="default"/>. This JSON object is restricted to
the Internet JSON (I-JSON) profile, as defined in <xref target="RFC7493"
format="default"/>.</t>
<t>The purpose of this JSON object is to provide Additional Information
to applications on a client host about the connectivity that is provided
using a given interface and source address. It typically includes data
that would be considered too large, or not critical enough, to be
provided within an RA option. The information contained in this object
<bcp14>MAY</bcp14> be used by the operating system, network libraries,
applications, or users in order to decide which set of PvDs should be
used for which connection, as described in <xref target="host"
format="default"/>.</t>
<t>The Additional Information related to a PvD is specifically intended
to be optional and is targeted at optimizing or informing the behavior
of user-facing hosts. This information can be extended to provide hints
for host system behavior (such as captive portal or walled-garden PvD
detection) or application behavior (describing application-specific
services offered on a given PvD). This content may not be appropriate
for light-weight IoT devices. IoT devices might
need only a subset of the information and would in some cases prefer a
smaller representation like Concise Binary Object Representation (CBOR)
<xref target="RFC7049" format="default"/>. Delivering a reduced version
of the PvD Additional Information designed for such devices is not
defined in this document.</t>
<section anchor="retr" numbered="true" toc="default">
<name>Retrieving the PvD Additional Information</name>
<t>When the H-flag of the PvD Option is set, hosts <bcp14>MAY</bcp14>
attempt to retrieve the PvD Additional Information associated with a
given PvD by performing an HTTP-over-TLS <xref target="RFC2818"
format="default"/> GET query to
<tt>https://&lt;PvD-ID&gt;/.well-known/pvd</tt>. Inversely, hosts
<bcp14>MUST NOT</bcp14> do so whenever the H-flag is not set.</t>
<t>Recommendations for how to use TLS securely can be found in <xref
target="RFC7525" format="default"/>.</t>
<t>When a host retrieves the PvD Additional Information, it
<bcp14>MUST</bcp14>
verify that the TLS server certificate is valid for the performed
request, specifically, that a DNS-ID <xref target="RFC6125" format="default"/>
on the certificate is equal to
the PvD ID expressed as an FQDN. This validation indicates that the
owner of the FQDN authorizes its use with the prefix advertised by the router.
If this validation fails, hosts <bcp14>MUST</bcp14> close the connection and
treat the PvD
as if it has no Additional Information.</t>
<t>HTTP requests and responses for PvD Additional Information use the
"application/pvd+json" media type (see <xref
target="pvd-json-media-type-registration" format="default"/>). Clients
<bcp14>SHOULD</bcp14> include this media type as an Accept header field in
their GET
requests, and servers <bcp14>MUST</bcp14> mark this media type as their
Content-Type
header field in responses.</t>
<t>Note that the DNS name resolution of the PvD ID, any connections
made
for certificate validation (such as Online Certificate Status Protocol (OCSP)
<xref target="RFC6960" format="default"/>), and
the HTTP request itself <bcp14>MUST</bcp14> be performed using the considered
PvD.
In other words, the name resolution, PKI checks, source address
selection, as well as the next-hop router selection <bcp14>MUST</bcp14> be
performed
while exclusively using the set of configuration information attached
with the PvD, as defined in <xref target="host" format="default"/>. In some
cases, it
may therefore be necessary to wait for an address to be available for
use (e.g., once the Duplicate Address Detection or DHCPv6 processes
are complete) before initiating the HTTP-over-TLS query. In order to
address privacy concerns around linkability of the PvD HTTP connection
with future user-initiated connections, if the host has a temporary address
per <xref target="RFC4941" format="default"/> in this PvD, then it
<bcp14>SHOULD</bcp14> use a temporary address
to fetch the PvD Additional Information and <bcp14>MAY</bcp14> deprecate the
used
temporary address and generate a new temporary address afterward.</t>
<t>If the HTTP status of the answer is greater than or equal to 400,
the host <bcp14>MUST</bcp14> close its connection and consider that
there is no PvD Additional Information. If the HTTP status of the
answer is between 300 and 399, inclusive, it <bcp14>MUST</bcp14>
follow the redirection(s). If the HTTP status of the answer is between
200 and 299, inclusive, the response is expected to be a single JSON
object.</t>
<t>After retrieval of the PvD Additional Information, hosts
<bcp14>MUST</bcp14> remember
the last Sequence Number value received in an RA including the same
PvD ID. Whenever a new RA for the same PvD is received with a different
Sequence Number value, or whenever the expiry date for the additional
information is reached, hosts <bcp14>MUST</bcp14> deprecate the Additional
Information
and stop using it.</t>
<t>Hosts retrieving a new PvD Additional Information object
<bcp14>MUST</bcp14> check
for the presence and validity of the mandatory fields specified in
<xref target="aiformat" format="default"/>. A retrieved object including an
expiration
time that is already past or missing a mandatory element <bcp14>MUST</bcp14>
be
ignored.</t>
<t>In order to avoid synchronized queries toward the server hosting
the PvD Additional Information when an object expires, object updates
are delayed by a randomized backoff time.</t>
<ul spacing="normal">
<li>When a host performs a JSON object update after it detected a
change in the PvD Option Sequence Number, it <bcp14>MUST</bcp14> add a delay
before sending the query. The target time for the delay is calculated
as a random time between zero and 2<sup>(10 + Delay)</sup> milliseconds,
where 'Delay' corresponds to the 4-bit unsigned integer in
the last received PvD Option.</li>
<li>When a host last retrieved a JSON object at time A that includes
an
expiry time B using the "expires" key, and the host is configured to keep
the PvD Additional Information up to date, it <bcp14>MUST</bcp14> add some
randomness into
its calculation of the time to fetch the update. The target time for
fetching the updated object is calculated as a uniformly random time
in the interval [(B-A)/2,B].</li>
</ul>
<t>In the example in <xref target="pvd_example" format="default"/>,
the
Delay field value is 1; this means that the host calculates its delay
by choosing a uniformly random time between 0 and 2<sup>(10 + 1)</sup>
milliseconds, i.e., between 0 and 2048 milliseconds.</t>
<t>Since the Delay value is directly within the PvD Option rather
than the object itself, an operator may perform a push-based update by
incrementing the Sequence Number value while changing the Delay value
depending on the criticality of the update and the capacity of its
PvD Additional Information servers.</t>
<t>In addition to adding a random delay when fetching Additional
Information, hosts
<bcp14>MUST</bcp14> enforce a minimum time between requesting Additional
Information
for a given PvD on the same network. This minimum time is
<bcp14>RECOMMENDED</bcp14>
to be 10 seconds, in order to avoid hosts causing a denial-of-service on the
PvD server. Hosts also <bcp14>MUST</bcp14> limit the number of requests that
are made to
different PvD Additional Information servers on the same network within a
short
period of time. A <bcp14>RECOMMENDED</bcp14> value is to issue no more than
five PvD
Additional Information requests in total on a given network within 10 seconds.
For more discussion, see <xref target="security" format="default"/>.</t>
<t>The PvD Additional Information object includes a set of IPv6
prefixes (under the key "prefixes") that <bcp14>MUST</bcp14> be checked
against all
the Prefix Information Options advertised in the RA. If any of the
prefixes included in any associated PIO is not covered by at least one of the
listed prefixes, the PvD Additional Information <bcp14>MUST</bcp14> be
considered
to be a misconfiguration and <bcp14>MUST NOT</bcp14> be used by the host. See
<xref target="misconfig" format="default"/> for more discussion on handling
such misconfigurations.</t>
<t>If the request for PvD Additional Information fails due to a TLS
certificate validation
error, an HTTP error, or because the retrieved file does not contain valid PvD
JSON,
hosts <bcp14>MUST</bcp14> close any connection used to fetch the PvD
Additional Information
and <bcp14>MUST NOT</bcp14> request the information for that PvD ID again for
the duration
of the local network attachment. If a host detects 10 or more such failures
to fetch PvD Additional Information, the local network is assumed to be
misconfigured or under attack and the host <bcp14>MUST NOT</bcp14> make any
further
requests for any PvD Additional Information, belonging to any PvD ID, for
the duration of the local network attachment. For more discussion, see <xref
target="security" format="default"/>.</t>
</section>
<section anchor="serverop" numbered="true" toc="default">
<name>Operational Consideration to Providing the PvD Additional
Information</name>
<t>Whenever the H-flag is set in the PvD Option, a valid PvD
Additional Information object <bcp14>MUST</bcp14> be made available to
all hosts receiving the RA by the network operator. In particular,
when a captive portal is present, hosts <bcp14>MUST</bcp14> still be
allowed to perform DNS, certificate validation, and HTTP-over-TLS
operations related to the retrieval of the object, even before logging
into the captive portal.</t>
<t>Routers <bcp14>SHOULD</bcp14> increment the PvD Option Sequence
Number by one whenever a new PvD Additional Information object is
available and should be retrieved by hosts. If the value exceeds what
can be stored in the Sequence Number field, it <bcp14>MUST</bcp14>
wrap back to zero.</t>
<t>The server providing the JSON files <bcp14>SHOULD</bcp14> also
check whether the client address is contained by the prefixes listed
in the Additional Information and <bcp14>SHOULD</bcp14> return a 403
response code if there is no match.</t>
</section>
<section anchor="aiformat" numbered="true" toc="default">
<name>PvD Additional Information Format</name>
<t>The PvD Additional Information is a JSON object.</t>
<t>The following table presents the mandatory keys, which
<bcp14>MUST</bcp14> be included in the object:</t>
<table align="center">
<thead>
<tr>
<th align="left">JSON key</th>
<th align="left">Description</th>
<th align="left">Type</th>
<th align="left">Example</th>
</tr>
</thead>
<tbody>
<tr>
<td align="left">identifier</td>
<td align="left">PvD ID FQDN</td>
<td align="left">String</td>
<td align="left">"pvd.example.com."</td>
</tr>
<tr>
<td align="left">expires</td>
<td align="left">Date after which this object is no longer
valid</td>
<td align="left">
<xref target="RFC3339" format="default"/> Date</td>
<td align="left">"2020-05-23T06:00:00Z"</td>
</tr>
<tr>
<td align="left">prefixes</td>
<td align="left">Array of IPv6 prefixes valid for this PvD</td>
<td align="left">Array of strings</td>
<td align="left">["2001:db8:1::/48", "2001:db8:4::/48"]</td>
</tr>
</tbody>
</table>
<t>A retrieved object that does not include all three of these keys at
the root of the JSON object <bcp14>MUST</bcp14> be ignored. All three keys
need
to be validated; otherwise, the object <bcp14>MUST</bcp14> be ignored. The
value stored
for "identifier" <bcp14>MUST</bcp14> be matched against the PvD ID FQDN
presented in the
PvD Option using the comparison mechanism described in <xref target="host"
format="default"/>.
The value stored for "expires" <bcp14>MUST</bcp14> be a valid date in the
future.
If the PIO of the received RA is not covered by at least one of the "prefixes"
key, the retrieved object <bcp14>SHOULD</bcp14> be ignored.</t>
<t>The following table presents some optional keys that
<bcp14>MAY</bcp14> be
included in the object.</t>
<table align="center">
<thead>
<tr>
<th align="left">JSON key</th>
<th align="left">Description</th>
<th align="left">Type</th>
<th align="left">Example</th>
</tr>
</thead>
<tbody>
<tr>
<td align="left">dnsZones</td>
<td align="left">DNS zones searchable and accessible</td>
<td align="left">Array of strings</td>
<td align="left">["example.com", "sub.example.com"]</td>
</tr>
<tr>
<td align="left">noInternet</td>
<td align="left">No Internet; set to "true" when the PvD is
restricted</td>
<td align="left">Boolean</td>
<td align="left">true</td>
</tr>
</tbody>
</table>
<t>It is worth noting that the JSON format allows for extensions.
Whenever an unknown key is encountered, it <bcp14>MUST</bcp14> be ignored
along with
its associated elements.</t>
<t>Private-use or experimental keys <bcp14>MAY</bcp14> be used in the
JSON
dictionary. In order to avoid such keys colliding with the keys registered by
IANA,
implementers or vendors defining private-use or experimental
keys <bcp14>MUST</bcp14> create sub-dictionaries. If a set of PvD Additional
Information keys
are defined by an organization that has a formal URN namespace <xref
target="IANA-URN" format="default"/>,
the URN namespace <bcp14>SHOULD</bcp14> be used as the top-level JSON key for
the sub-dictionary. For other private uses, the sub-dictionary key
<bcp14>SHOULD</bcp14> follow the format of "vendor-*", where the "*" is
replaced by the
implementer's or vendor's identifier. For example, keys specific to the FooBar
organization could use "vendor-foobar". If a host receives a sub-dictionary
with
an unknown key, the host <bcp14>MUST</bcp14> ignore the contents of the
sub-dictionary.</t>
<section anchor="example" numbered="true" toc="default">
<name>Example</name>
<t>The following two examples show how the JSON keys defined in this
document can be used:</t>
<sourcecode type="json">
{
"identifier": "cafe.example.com.",
"expires": "2020-05-23T06:00:00Z",
"prefixes": ["2001:db8:1::/48", "2001:db8:4::/48"],
}
{
"identifier": "company.foo.example.com.",
"expires": "2020-05-23T06:00:00Z",
"prefixes": ["2001:db8:1::/48", "2001:db8:4::/48"],
"vendor-foo":
{
"private-key": "private-value",
},
}
</sourcecode>
</section>
</section>
<section anchor="misconfig" numbered="true" toc="default">
<name>Detecting Misconfiguration and Misuse</name>
<t>Hosts <bcp14>MUST</bcp14> validate the TLS server certificate when
retrieving PvD
Additional Information, as detailed in <xref target="retr"
format="default"/>.</t>
<t>Hosts <bcp14>MUST</bcp14> verify that all prefixes in all the RA
PIOs are covered by a
prefix from the PvD Additional Information. An adversarial router
attempting to spoof the definition of an Explicit PvD, without the ability to
modify the PvD Additional Information, would need to perform IPv6-to-IPv6
Network
Prefix Translation (NPTv6) <xref target="RFC6296" format="default"/> in order
to circumvent this check.
Thus, this check cannot prevent all spoofing, but it can detect
misconfiguration
or mismatched routers that are not adding a NAT.</t>
<t>If NPTv6 is being added in order to spoof PvD ownership, the HTTPS
server for Additional Information can detect this misconfiguration.
The HTTPS server <bcp14>SHOULD</bcp14> validate the source addresses
of incoming connections (see <xref target="retr"
format="default"/>). This check gives reasonable assurance that
NPTv6 was not used and restricts the information to the valid network
users.If the PvD does not
provision IPv4 (it does not include the L-flag in the RA), the server
cannot validate the source addresses of connections using IPv4. Thus,
the PvD ID FQDN for such PvDs <bcp14>SHOULD NOT</bcp14> have a DNS A
record.</t>
</section>
</section>
<section anchor="operational-considerations" numbered="true"
toc="default">
<name>Operational Considerations</name>
<t>This section describes some example use cases of PvDs. For the sake
of
simplicity, the RA messages will not be described in the usual ASCII art
but rather in an indented list. Values in the PvD Option header that are not
included in the example are assumed to be zero or false (such as the
H-flag, Sequence Number, and Delay fields).</t>
<section anchor="exposing-extra-ra-options-to-pvd-aware-hosts"
numbered="true" toc="default">
<name>Exposing Extra RA Options to PvD-Aware Hosts</name>
<t>In this example, there is one RA message sent by the router. This
message contains some options applicable to all hosts on the network
and also a PvD Option that also contains other options only visible to
PvD-aware hosts.</t>
<ul spacing="normal">
<li>RA Header: router lifetime = 6000</li>
<li>Prefix Information Option: length = 4, prefix =
2001:db8:cafe::/64</li>
<li>
<t>PvD Option header: length = 3 + 5 + 4, PvD ID FQDN =
example.org., R-flag = 0 (actual length of the header with padding
24 bytes = 3 * 8 bytes)
</t>
<ul spacing="normal">
<li>Recursive DNS Server: length = 5, addresses =
[2001:db8:cafe::53, 2001:db8:f00d::53]</li>
<li>Prefix Information Option: length = 4, prefix =
2001:db8:f00d::/64</li>
</ul>
</li>
</ul>
<t>Note that a PvD-aware host will receive two different prefixes,
<tt>2001:db8:cafe::/64</tt> and <tt>2001:db8:f00d::/64</tt>, both
associated
with the same PvD (identified by "example.org."). A non-PvD-aware
host will only receive one prefix, <tt>2001:db8:cafe::/64</tt>.</t>
</section>
<section anchor="different-ras-for-pvd-aware-and-non-pvd-aware-hosts"
numbered="true" toc="default">
<name>Different RAs for PvD-Aware and Non-PvD-Aware Hosts</name>
<t>It is expected that for some years, networks will have a mixed
environment of PvD-aware hosts and non-PvD-aware hosts. If there is a
need to give specific information to PvD-aware hosts only, then it is
<bcp14>RECOMMENDED</bcp14> to send two RA messages, one for each class of
hosts.
This approach allows for two distinct sets of configuration information
to be sent in a way that will not disrupt non-PvD-aware hosts. It also
lowers the risk that a single RA message will approach its MTU limit due
to duplicated information.</t>
<t>If two RA messages are sent for this reason, they
<bcp14>MUST</bcp14> be sent from two
different link-local source addresses (<xref target="router"
format="default"/>). For example, here is the
RA sent for non-PvD-aware hosts:</t>
<ul spacing="normal">
<li>RA Header: router lifetime = 6000 (non-PvD-aware hosts will use
this router as a default router)</li>
<li>Prefix Information Option: length = 4, prefix =
2001:db8:cafe::/64</li>
<li>Recursive DNS Server Option: length = 3, addresses =
[2001:db8:cafe::53]</li>
<li>
<t>PvD Option header: length = 3 + 2, PvD ID FQDN =
foo.example.org., R-flag = 1 (actual length of the header 24 bytes
= 3 * 8 bytes)
</t>
<ul spacing="normal">
<li>RA Header: router lifetime = 0 (PvD-aware hosts will not use
this router as a default router), implicit length = 2</li>
</ul>
</li>
</ul>
<t>And here is the RA sent for PvD-aware hosts:</t>
<ul spacing="normal">
<li>RA Header: router lifetime = 0 (non-PvD-aware hosts will not use
this router as a default router)</li>
<li>
<t>PvD Option header: length = 3 + 2 + 4 + 3, PvD ID FQDN =
bar.example.org., R-flag = 1 (actual length of the header 24 bytes
= 3 * 8 bytes)
</t>
<ul spacing="normal">
<li>RA Header: router lifetime = 1600 (PvD-aware hosts will use
this router as a default router), implicit length = 2</li>
<li>Prefix Information Option: length = 4, prefix =
2001:db8:f00d::/64</li>
<li>Recursive DNS Server Option: length = 3, addresses =
[2001:db8:f00d::53]</li>
</ul>
</li>
</ul>
<t>In the above example, non-PvD-aware hosts will only use the first
listed RA sent by their default router and use the
<tt>2001:db8:cafe::/64</tt> prefix. PvD-aware hosts will autonomously
configure addresses from both PIOs but will only use the source
address in <tt>2001:db8:f00d::/64</tt> to communicate past the
first-hop router
since only the router sending the second RA will be used as the
default
router; similarly, they will use the DNS server
<tt>2001:db8:f00d::53</tt> when
communicating from this address.</t>
</section>
<section anchor="enabling-multi-homing-for-pvd-aware-hosts"
numbered="true" toc="default">
<name>Enabling Multihoming for PvD-Aware Hosts</name>
<t>In this example, the goal is to have one prefix from one RA be
usable by both non-PvD-aware and PvD-aware hosts and to have another
prefix usable only by PvD-aware hosts. This allows PvD-aware hosts to
be able to effectively multihome on the network.</t>
<t>The first RA is usable by all hosts. The only difference for
PvD-aware hosts is that they can explicitly identify the PvD ID
associated with the RA. PvD-aware hosts will also use this prefix to
communicate with non-PvD-aware hosts on the same network.</t>
<ul spacing="normal">
<li>RA Header: router lifetime = 6000 (non-PvD-aware hosts will use
this router as a default router)</li>
<li>Prefix Information Option: length = 4, prefix =
2001:db8:cafe::/64</li>
<li>Recursive DNS Server Option: length = 3, addresses =
[2001:db8:cafe::53]</li>
<li>PvD Option header: length = 3, PvD ID FQDN = foo.example.org.,
R-flag = 0 (actual length of the header 24 bytes = 3 * 8 bytes)</li>
</ul>
<t>The second RA contains a prefix usable only by PvD-aware
hosts. Non-PvD-aware
hosts will ignore this RA; hence, only the PvD-aware hosts will be
multihomed.</t>
<ul spacing="normal">
<li>RA Header: router lifetime = 0 (non-PvD-aware hosts will not use
this router as a default router)</li>
<li>
<t>PvD Option header: length = 3 + 2 + 4 + 3, PvD ID FQDN =
bar.example.org., R-flag = 1 (actual length of the header 24 bytes
= 3 * 8 bytes)
</t>
<ul spacing="normal">
<li>RA Header: router lifetime = 1600 (PvD-aware hosts will use
this router as a default router), implicit length = 2</li>
<li>Prefix Information Option: length = 4, prefix =
2001:db8:f00d::/64</li>
<li>Recursive DNS Server Option: length = 3, addresses =
[2001:db8:f00d::53]</li>
</ul>
</li>
</ul>
<t>Note: the above examples assume that the router has received its
PvD IDs from upstream routers
or via some other configuration mechanism. Another document could define ways
for the router
to generate its own PvD IDs to allow the above scenario in the absence of PvD
ID provisioning.</t>
</section>
<section anchor="providing-additional-information-to-pvd-aware-hosts"
numbered="true" toc="default">
<name>Providing Additional Information to PvD-Aware Hosts</name>
<t>In this example, the router indicates that it provides Additional
Information using the H-flag.
The Sequence Number on the PvD Option is set to 7 in this example.</t>
<ul spacing="normal">
<li>RA Header: router lifetime = 6000</li>
<li>Prefix Information Option: length = 4, prefix =
2001:db8:cafe::/64</li>
<li>Recursive DNS Server Option: length = 3, addresses =
[2001:db8:cafe::53]</li>
<li>PvD Option header: length = 3, PvD ID FQDN = cafe.example.com.,
Sequence Number = 7, R-flag = 0, H-flag = 1 (actual length of the header with
padding
24 bytes = 3 * 8 bytes)</li>
</ul>
<t>A PvD-aware host will fetch
&lt;https://cafe.example.com/.well-known/pvd&gt; to get the additional
information. The following example shows a GET request that the host
sends, in HTTP/2 syntax <xref target="RFC7540" format="default"/>:</t>
<sourcecode>
:method = GET
:scheme = https
:authority = cafe.example.com
:path = /.well-known/pvd
accept = application/pvd+json
</sourcecode>
<t>The HTTP server will respond with the JSON Additional
Information:</t>
<sourcecode type="json">
:status = 200
content-type = application/pvd+json
content-length = 116
{
"identifier": "cafe.example.com.",
"expires": "2020-05-23T06:00:00Z",
"prefixes": ["2001:db8:cafe::/48"],
}
</sourcecode>
<t>At this point, the host has the PvD Additional Information and
knows
the expiry time. When either the expiry time passes or a new
Sequence Number is provided in an RA, the host will re-fetch the
Additional Information.</t>
<t>For example, if the router sends a new RA with the Sequence Number
set to 8,
the host will re-fetch the Additional Information:</t>
<ul spacing="normal">
<li>PvD Option header: length = 3 + 5 + 4 , PvD ID FQDN =
cafe.example.com.,
Sequence Number = 8, R-flag = 0, H-flag = 1 (actual length of the header with
padding
24 bytes = 3 * 8 bytes)</li>
</ul>
<t>However, if the router sends a new RA, but the Sequence Number has
not changed,
the host would not re-fetch the Additional Information (until and unless the
expiry time
of the Additional Information has passed).</t>
</section>
</section>
<section anchor="security" numbered="true" toc="default">
<name>Security Considerations</name>
<t>Since the PvD Option can contain an RA header and other RA options,
any security considerations that apply for specific RA options continue to
apply when used within a PvD Option.</t>
<t>Although some solutions such as IPsec or SEcure Neighbor Discovery
(SeND) <xref target="RFC3971" format="default"/> can be used in order to
secure the IPv6 Neighbor Discovery Protocol, in practice, actual
deployments largely rely on link-layer or physical-layer security
mechanisms (e.g., 802.1x <xref target="IEEE8021X" format="default"/>) in
conjunction with RA-Guard <xref target="RFC6105" format="default"/>.</t>
<t>If multiple RAs are sent for a single PvD to avoid fragmentation,
dropping packets
can lead to processing only part of a PvD Option, which could lead to hosts
receiving only part of the contained options. As discussed in <xref
target="router" format="default"/>, routers
<bcp14>MUST</bcp14> include the PvD Option in all fragments generated.</t>
<t>This specification does not improve the Neighbor Discovery Protocol
security model but simply validates that the owner of the PvD FQDN
authorizes its use with the prefix advertised by the router. In
combination with implicit trust in the local router (if present), this
gives the host some level of assurance that the PvD is authorized for
use in this environment. However, when the local router cannot be
trusted, no such guarantee is available.</t>
<t>It must be noted that <xref target="misconfig" format="default"/> of
this document
only provides reasonable assurance against misconfiguration but does not
prevent a hostile network access provider from advertising incorrect
information that could lead applications or hosts to select a hostile PvD.
However, a host that correctly implements the multiple PvD architecture <xref
target="RFC7556" format="default"/>
using the mechanism described in this document will be less susceptible to
some attacks than a host that does not by being able to check for the various
misconfigurations or inconsistencies described in this document.</t>
<t>Since expiration times provided in PvD Additional Information use
absolute time, these values can be skewed due to clock skew or for hosts
without an accurate time base. Such time values <bcp14>MUST NOT</bcp14>
be used for security-sensitive functionality or decisions.</t>
<t>An attacker generating RAs on a local network can use the H-flag and
the PvD ID
to cause hosts on the network to make requests for PvD Additional Information
from servers. This can become a denial-of-service attack, in which an attacker
can amplify its attack by triggering TLS connections to arbitrary servers in
response
to sending UDP packets containing RA messages. To mitigate this attack, hosts
<bcp14>MUST</bcp14>:</t>
<ul spacing="normal">
<li>limit the rate at which they fetch a particular PvD's Additional
Information;</li>
<li>limit the rate at which they fetch any PvD Additional Information
on a given local
network;</li>
<li>stop making requests for a PvD ID that does not respond with valid
JSON; and</li>
<li>stop making requests for all PvD IDs once a certain number of
failures is reached
on a particular network.</li>
</ul>
<t>Details are provided in <xref target="retr" format="default"/>. This
attack can be targeted at generic web servers,
in which case the host behavior of stopping requesting for any server that
doesn't
behave like a PvD Additional Information server is critical. Limiting requests
for
a specific PvD ID might not be sufficient if the attacker changes the PvD ID
values
quickly, so hosts also need to stop requesting if they detect consistent
failure when
on a network that is under attack. For cases in which an attacker is pointing
hosts at
a valid PvD Additional Information server (but one that is not actually
associated
with the local network), the server <bcp14>SHOULD</bcp14> reject any requests
that do not originate
from the expected IPv6 prefix as described in <xref target="serverop"
format="default"/>.</t>
</section>
<section anchor="privacy-considerations" numbered="true" toc="default">
<name>Privacy Considerations</name>
<t>Retrieval of the PvD Additional Information over HTTPS requires early
communications between the connecting host and a server that may be
located further than the first-hop router. Although this server is
likely to be located within the same administrative domain as the
default router, this property can't be ensured. To minimize the leakage
of identity information while retrieving the PvD Additional Information,
hosts <bcp14>SHOULD</bcp14> make use of an IPv6 temporary address and
<bcp14>SHOULD NOT</bcp14> include any privacy-sensitive data, such as a
User-Agent header field or an HTTP cookie.</t>
<t>Hosts might not always fetch PvD Additional Information, depending on
whether or not they expect to use the information. However, if a host
allows requesting Additional Information for certain PvD IDs,
an attacker could send various PvD IDs in RAs to detect
which PvD IDs are allowed by the client. To avoid this, hosts
<bcp14>SHOULD</bcp14> either fetch Additional Information for all
eligible PvD IDs on a given local network or fetch the information for
none of them.</t>
<t>From a user privacy perspective, retrieving the PvD Additional
Information
is not different from establishing a first connection to a remote
server or even performing a single DNS lookup. For example, most
operating systems already perform early queries to static web sites,
such as &lt;http://captive.example.com/hotspot-detect.html&gt;, in order to
detect the presence of a captive portal.</t>
<t>The DNS queries associated with the PvD Additional Information
<bcp14>MUST</bcp14>
use the DNS servers indicated by the associated PvD, as described in
<xref target="retr" format="default"/>. This ensures the name of the PvD
Additional Information server
is not unintentionally sent on another network, thus leaking identifying
information about the networks with which the client is associated.</t>
<t>There may be some cases where hosts, for privacy reasons, should
refrain from accessing servers that are located outside a certain
network boundary. In practice, this could be implemented as an allowed list
of 'trusted' FQDNs and/or IP prefixes that the host is allowed to
communicate with. In such scenarios, the host <bcp14>SHOULD</bcp14> check that
the
provided PvD ID, as well as the IP address that it resolves into, are
part of the allowed list.</t>
<t>Network operators <bcp14>SHOULD</bcp14> restrict access to PvD
Additional
Information to only expose it to hosts that are connected to the local
network, especially if the Additional Information would provide information
about local network configuration to attackers. This can be implemented by
allowing access from the addresses and prefixes that the router provides
for the PvD, which will match the prefixes contained in the PvD Additional
Information. This technique is described in <xref target="serverop"
format="default"/>.</t>
</section>
<section anchor="iana" numbered="true" toc="default">
<name>IANA Considerations</name>
<section
anchor="change-to-ipv6-neighbor-discovery-option-formats-registry"
numbered="true" toc="default">
<name>Change to IPv6 Neighbor Discovery Option Formats Registry</name>
<t>IANA has removed the
'reclaimable' tag for value 21 for the PvD Option in the
"IPv6 Neighbor Discovery Option Formats" registry.</t>
</section>
<section anchor="new-entry-in-the-well-known-uris-registry"
numbered="true" toc="default">
<name>New Entry in the Well-Known URIs Registry</name>
<t>IANA has added a new entry in the "Well-Known URIs" registry
<xref target="RFC8615" format="default"/> with the following
information:</t>
<t>URI suffix: pvd</t>
<t>Change controller: IETF</t>
<t>Specification document: RFC 8801</t>
<t>Status: permanent</t>
<t>Related information: N/A</t>
</section>
<section anchor="additional-information-pvd-keys-registry"
numbered="true" toc="default">
<name>New Additional Information PvD Keys Registry</name>
<t>IANA has created and will maintain a new registry called
"Additional Information PvD Keys", which reserves JSON keys for use in
PvD Additional Information. The initial contents of this registry are
given in <xref target="aiformat" format="default"/> (both
the table of mandatory keys and the table of optional keys).</t>
<t>The status of a key as mandatory or optional is intentionally not
denoted in the table to allow for flexibility in future use cases.
Any new assignments of keys will be considered as optional for the
purpose of the mechanism described in this document.</t>
<t>New assignments in the "Additional Information PvD Keys" registry
will be administered by IANA through Expert Review <xref
target="RFC8126" format="default"/>. Experts are requested to ensure
that defined keys do not overlap in names or semantics and that they
represent
non-vendor-specific use cases. Vendor-specific keys
<bcp14>SHOULD</bcp14> use sub-dictionaries, as described in <xref
target="aiformat" format="default"/>.</t>
<t>IANA has placed the "Additional Information PvD Keys" registry
within a new registry entitled "Provisioning Domains (PvDs)".</t>
</section>
<section anchor="pvd-option-flags-registry" numbered="true"
toc="default">
<name>New PvD Option Flags Registry</name>
<t>IANA has also created and will maintain a new registry entitled
"PvD Option Flags". This new registry reserves bit positions from 0
to 11 to be used in the PvD Option bitmask. This document assigns bit
positions 0, 1, and 2 as shown in the table below. Future assignments
require Standards Action <xref target="RFC8126"
format="default"/>.</t>
<table anchor="iana-flags">
<thead>
<tr>
<th>Bit</th>
<th>Name</th>
<th>Reference</th>
</tr>
</thead>
<tbody>
<tr>
<td>0</td>
<td>H-flag</td>
<td>RFC 8801</td>
</tr>
<tr>
<td>1</td>
<td>L-flag</td>
<td>RFC 8801</td>
</tr>
<tr>
<td>2</td>
<td>R-flag</td>
<td>RFC 8801</td>
</tr>
<tr>
<td>3-11</td>
<td>Unassigned</td>
<td></td>
</tr>
</tbody>
</table>
<t>Since these flags apply to an IPv6 Router Advertisement Option,
IANA has placed this registry under the existing "Internet
Control Message Protocol version 6 (ICMPv6) Parameters" registry and
provided a link on the new "Provisioning Domains (PvDs)" registry.</t>
</section>
<section anchor="pvd-json-media-type-registration" numbered="true"
toc="default">
<name>PvD JSON Media Type Registration</name>
<t>This document registers the media type for PvD JSON text,
"application/pvd+json".</t>
<dl>
<dt>Type name:</dt><dd>application</dd>
<dt>Subtype name:</dt><dd>pvd+json</dd>
<dt>Required parameters:</dt><dd>N/A</dd>
<dt>Optional parameters:</dt><dd>N/A</dd>
<dt>Encoding considerations:</dt><dd>Encoding considerations are
identical to
those specified for the "application/json" media type.</dd>
<dt>Security considerations:</dt><dd>See <xref target="security"
format="default"/> of RFC 8801.</dd>
<dt>Interoperability considerations:</dt><dd>This document specifies
the format of
conforming messages and the interpretation thereof.</dd>
<dt>Published specification:</dt><dd>RFC 8801</dd>
<dt>Applications that use this media type:</dt><dd>This media type is
intended
to be used by networks advertising additional Provisioning Domain
information and clients looking up such information.</dd>
<dt>Fragment identifier considerations:</dt><dd>N/A</dd>
<dt>Additional information:</dt><dd>N/A</dd>
<dt>Person &amp; email address to contact for further
information:</dt><dd>See
Authors' Addresses section</dd>
<dt>Intended usage:</dt><dd>COMMON</dd>
<dt>Restrictions on usage:</dt><dd>N/A</dd>
<dt>Author:</dt><dd>IETF</dd>
<dt>Change controller:</dt><dd>IETF</dd>
</dl>
</section>
</section>
</middle>
<back>
<displayreference target="I-D.kline-mif-mpvd-api-reqs" to="MPVD-API"/>
<displayreference target="I-D.stenberg-mif-mpvd-dns" to="MPVD-DNS"/>
<references>
<name>References</name>
<references>
<name>Normative References</name>
<xi:include
href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7556.xml"/>
<xi:include
href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4861.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.8174.xml"/>
<xi:include
href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.1035.xml"/>
<xi:include
href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6980.xml"/>
<xi:include
href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4191.xml"/>
<xi:include
href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4343.xml"/>
<xi:include
href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6724.xml"/>
<xi:include
href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8028.xml"/>
<xi:include
href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8259.xml"/>
<xi:include
href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7493.xml"/>
<xi:include
href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2818.xml"/>
<xi:include
href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7525.xml"/>
<xi:include
href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4941.xml"/>
<xi:include
href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.3339.xml"/>
<xi:include
href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8615.xml"/>
<xi:include
href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8126.xml"/>
</references>
<references>
<name>Informative References</name>
<xi:include
href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8106.xml"/>
<xi:include
href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.3646.xml"/>
<xi:include
href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2131.xml"/>
<xi:include
href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6146.xml"/>
<xi:include
href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4389.xml"/>
<xi:include
href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7278.xml"/>
<xi:include
href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8415.xml"/>
<xi:include
href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6147.xml"/>
<xi:include
href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7049.xml"/>
<xi:include
href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6125.xml"/>
<xi:include
href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6960.xml"/>
<xi:include
href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6296.xml"/>
<xi:include
href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7540.xml"/>
<xi:include
href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.3971.xml"/>
<xi:include
href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6105.xml"/>
<reference anchor="IEEE8021X"
target="https://ieeexplore.ieee.org/document/9018454">
<front>
<title>IEEE Standard for Local and Metropolitan Area Networks --
Port-Based Network Access Control</title>
<author>
<organization>IEEE</organization>
</author>
</front>
<seriesInfo name="IEEE" value="802.1X-2020"/>
<seriesInfo name="DOI" value="10.1109/IEEESTD.2020.9018454"/>
</reference>
<reference anchor="IANA-URN"
target="https://www.iana.org/assignments/urn-namespaces/">
<front>
<title>Uniform Resource Names (URN) Namespaces</title>
<author>
<organization>IANA</organization>
</author>
</front>
</reference>
<xi:include
href="https://xml2rfc.ietf.org/public/rfc/bibxml3/reference.I-D.kline-mif-mp
vd-api-reqs.xml"/>
<xi:include
href="https://xml2rfc.ietf.org/public/rfc/bibxml3/reference.I-D.stenberg-mif
-mpvd-dns.xml"/>
</references>
</references>
<section anchor="acknowledgments" numbered="false" toc="default">
<name>Acknowledgments</name>
<t>Many thanks to <contact fullname="Markus Stenberg"/> and <contact
fullname="Steven Barth"/> for their earlier work on <xref
target="I-D.stenberg-mif-mpvd-dns" format="default"/>, as well as to
<contact fullname="Basile Bruneau"/>, who was author of an early draft
version
of this document.</t>
<t>Thanks also to <contact fullname="Marcus Keane"/>, <contact
fullname="Mikael Abrahamsson"/>, <contact fullname="Ray Bellis"/>,
<contact fullname="Zhen Cao"/>, <contact fullname="Tim Chown"/>,
<contact fullname="Lorenzo Colitti"/>, <contact fullname="Michael Di
Bartolomeo"/>, <contact fullname="Ian Farrer"/>, <contact
fullname="Phillip Hallam-Baker"/>, <contact fullname="Bob Hinden"/>,
<contact fullname="Tatuya Jinmei"/>, <contact fullname="Erik Kline"/>,
<contact fullname="Ted Lemon"/>, <contact fullname="Paul Hoffman"/>,
<contact fullname="Dave Thaler"/>, <contact fullname="Suresh
Krishnan"/>, <contact fullname="Gorry Fairhurst"/>, <contact
fullname="Jen Lenkova"/>, <contact fullname="Veronika McKillop"/>,
<contact fullname="Mark Townsley"/>, and <contact fullname="James
Woodyatt"/> for useful and interesting discussions and reviews.</t>
<t>Finally, special thanks to <contact fullname="Thierry Danis"/> for
his valuable input and implementation efforts, <contact fullname="Tom
Jones"/> for his integration effort into the NEAT project, and <contact
fullname="Rigil Salim"/> for his implementation work.</t>
</section>
</back>
</rfc>
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