Network Working Group                                         P. Pfister
Internet-Draft                                                 E. Vyncke
Intended status: Standards Track                                   Cisco
Expires: February 13, April 2, 2020                                          T. Pauly
                                                              Apple Inc.
                                                             D. Schinazi
                                                              Google LLC
                                                                 W. Shao
                                                                   Cisco
                                                         August 12,
                                                      September 30, 2019

             Discovering Provisioning Domain Names and Data
               draft-ietf-intarea-provisioning-domains-06
               draft-ietf-intarea-provisioning-domains-07

Abstract

   Provisioning Domains (PvDs) are defined as consistent sets of network
   configuration information.  This 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.

   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 additional PvD information that can be
   retrieved using HTTP over TLS.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on February 13, April 2, 2020.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Specification of Requirements . . . . . . . . . . . . . .   4
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Provisioning Domain Identification using Router
       Advertisements  . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  PvD ID Option for Router Advertisements . . . . . . . . .   5
     3.2.  Router Behavior . . . . . . . . . . . . . . . . . . . . .   8
     3.3.  Non-PvD-aware Host Behavior . . . . . . . . . . . . . . .   9
     3.4.  PvD-aware Host Behavior . . . . . . . . . . . . . . . . .   9
       3.4.1.  DHCPv6 configuration association  . . . . . . . . . .  10
       3.4.2.  DHCPv4 configuration association  . . . . . . . . . .  10
       3.4.3.  Connection Sharing by the Host  . . . . . . . . . . .  11
       3.4.4.  Usage of DNS Servers  . . . . . . . . . . . . . . . .  12
   4.  Provisioning Domain Additional Information  . . . . . . . . .  12
     4.1.  Retrieving the PvD Additional Information . . . . . . . .  13
     4.2.  Operational Consideration to Providing the PvD Additional
           Information . . . . . . . . . . . . . . . . . . . . . . .  15
     4.3.  PvD Additional Information Format . . . . . . . . . . . .  15
       4.3.1.  Example . . . . . . . . . . . . . . . . . . . . . . .  17
     4.4.  Detecting misconfiguration and misuse . . . . . . . . . .  17
   5.  Operational Considerations  . . . . . . . . . . . . . . . . .  18
     5.1.  Exposing Extra RA Options to PvD-Aware Hosts  . . . . . .  18
     5.2.  Different RAs for PvD-Aware and Non-PvD-Aware Hosts . . .  18
     5.3.  Enabling Multi-homing for PvD-Aware Hosts . . . . . . . .  19
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  20
   7.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  21
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  21
     8.1.  Additional Information PvD Keys Registry  . . . . . . . .  22
     8.2.  PvD Option Flags Registry . . . . . . . . . . . . . . . .  22
     8.3.  PvD JSON Media Type Registration  . . . . . . . . . . . .  22
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  23
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  23
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  23
     10.2.  Informative References . . . . . . . . . . . . . . . . .  24
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  27  26

1.  Introduction

   Provisioning Domains (PvDs) are defined in [RFC7556] 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.

   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.

   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), [RFC7556] 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:

   1.  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.

   2.  The ability to associate additional informations about PvDs to
       describe the properties of the network.

   While [RFC7556] 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.

   This document specifies a way to identify PvDs with Fully Qualified
   Domain Names (FQDN), called PvD IDs.  Those identifiers are
   advertised in a new Router Advertisement (RA) [RFC4861] option called
   the PvD ID Router Advertisement 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,
   deriving from it.  The PVD ID Router Advertisement option may also
   contain a set of other RA options.  Since such options are only
   considered by hosts implementing this specification, network
   operators may configure hosts that are 'PvD-aware' with PvDs that are
   ignored by other hosts.

   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.

   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 an 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.

   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.

1.1.  Specification of Requirements

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Terminology

   This document uses the following terminology:

   Provisioning Domain (PvD):  A set of network configuration
      information; for more information, see [RFC7556].

   PvD ID:  A Fully Qualified Domain Name (FQDN) used to identify a PvD.

   Explicit PvD:  A PvD uniquely identified with a PvD ID.  For more
      information, see [RFC7556].

   Implicit PvD:  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 [RFC7556].

   PvD-aware host:  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
      [RFC7556].

3.  Provisioning Domain Identification using Router Advertisements

   Explicit PvDs are identified by a PvD ID.  The PvD ID is a Fully
   Qualified Domain Name (FQDN) which MUST belong to the network
   operator in order to avoid naming collisions.  The same PvD ID MAY 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 MUST be different to follow Section 2.4 of
   [RFC7556].

3.1.  PvD ID Option for Router Advertisements

   This document introduces a Router Advertisement (RA) option called
   PvD Option.  It is used to convey the FQDN identifying a given PvD
   (see Figure 1, bind the PvD ID with configuration information
   received over DHCPv4 (see Section 3.4.2), enable the use of HTTP over
   TLS to retrieve the PvD Additional Information JSON object (see
   Section 4), as well as contain any other RA options which would
   otherwise be valid in the RA.

    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 ...
   +-+-+-+-+-+-+-+-+-+-+-+-

           Figure 1: PvD ID Router Advertisements Option Format

   Type:  (8 bits) Set to 21.

   Length:  (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.

   H-flag:  (1 bit) 'HTTP' flag stating whether some PvD Additional
      Information is made available through HTTP over TLS, as described
      in Section 4.

   L-flag:  (1 bit) 'Legacy' flag stating whether the router is also
      providing IPv4 information using DHCPv4 (see Section 3.4.2).

   R-flag:  (1 bit) 'Router Advertisement' flag stating whether the PvD
      Option is followed (right after padding to the next 64 bits
      boundary) by a Router Advertisement message header (See section
      4.2 of [RFC4861]).

   Delay:  (4 bits) Unsigned integer used to delay HTTP GET queries from
      hosts by a randomized backoff (see Section 4.1).

   Reserved:  (13 bits) Reserved for later use.  It MUST be set to zero
      by the sender and ignored by the receiver.

   Sequence Number:  (16 bits) Sequence number for the PvD Additional
      Information, as described in Section 4.

   PvD ID FQDN:  The FQDN used as PvD ID encoded in DNS format, as
      described in Section 3.1 of [RFC1035].  Domain names compression
      described in Section 4.1.4 of [RFC1035] MUST NOT be used.

   Padding:  Zero or more padding octets to the next 8 octet boundary
      (see Section 4.6 of [RFC4861]).  It MUST be set to zero by the
      sender, and ignored by the receiver.

   RA message header:  (16 octets) When the R-flag is set, a full Router
      Advertisement message header as specified in [RFC4861].  The
      sender MUST set the 'Type' to 134, the value for "Router
      Advertisement", and set the 'Code' to 0.  Receivers MUST ignore
      both of these fields.  The 'Checksum' MUST be set to 0 by the
      sender; non-zero checksums MUST be ignored by the receiver.  All
      other fields are to be set and parsed as specified in [RFC4861] or
      any updating documents.

   Options:  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 such as to be ignored by hosts that are
      not PvD-aware.

   Here is an example of a PvD Option with "example.org" as the PvD ID
   FQDN and including both an RDNSS option and a prefix information
   option.  It has a Sequence Number of 123, and indicates the presence
   of additional information that is expected to be fetched with a delay
   factor of 5.

    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:5|
   +---------------+-------------------------------+---------------+
   |       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 6106) length: 5                          ...
   ...                                                           ...
   ...                                                             |
   +---------------------------------------------------------------+
   | Prefix Information Option (RFC 4861) length: 4              ...
   ...                                                             |
   ...                                                             |
   +---------------------------------------------------------------+

                                 Figure 2

3.2.  Router Behavior

   A router MAY send RAs containing one PvD Option, but MUST NOT include
   more than one PvD Option in each RA.  The PvD Option MUST NOT contain
   further PvD Options.

   The PvD Option MAY contain zero, one, or more RA options which would
   otherwise be valid as part of the same RA.  Such options are
   processed by PvD-aware hosts, while ignored by other hosts per
   section 4.2 of [RFC4861].

   In order to provide multiple different PvDs, a router MUST send
   multiple RAs.  If more than one different Implicit PvDs are
   advertised, the RAs MUST be sent from different link-local source
   addresses.  Explicit PvDs MAY share link-local source addresses with
   an Implicit PvD and any number of other Explicit PvDs.

   In other words, different Explicit PvDs MAY be advertised with RAs
   using the same link-local source address; but different Implicit
   PvDs, advertised by different RAs, MUST use different link-local
   addresses because these Implicit PvDs are identified by the source
   addresses of the RAs.

   As specified in [RFC4861], when the set of options causes the size of
   an advertisement to exceed the link MTU, multiple router
   advertisements can be sent, each containing a subset of the options.
   In such cases, the PvD Option header (i.e., all fields except the
   'Options' field) MUST be repeated in all the transmitted RAs.  The
   options within the 'Options' field, MAY be transmitted only once,
   included in one of the transmitted PvD Options.

3.3.  Non-PvD-aware Host Behavior

   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
   section 4.2 of [RFC4861].  This ensure the backward compatibility
   required in Section 3.3 of [RFC7556].  This behavior allows for a
   mixed-mode network with a mix of PvD-aware and non-PvD-aware hosts
   coexist.

3.4.  PvD-aware Host Behavior

   Hosts MUST associate received RAs and included configuration
   information (e.g., Router Valid Lifetime, Prefix Information
   [RFC4861], Recursive DNS Server [RFC8106], Routing Information
   [RFC4191] 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.

   In case multiple PvD Options are found in a given RA, hosts MUST
   ignore all but the first PvD Option.

   If a host receives PvD Options flags that it does not recognize
   (currently in the Reserved field), it MUST ignore these flags.

   Similarly, hosts MUST associate all network configuration objects
   (e.g., default routers, addresses, more specific routes, DNS
   Recursive Resolvers) with the PvD associated with the RA which last
   updated 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 which included the given PIO.

   PvD IDs MUST be compared in a case-insensitive manner as defined by
   [RFC4343].  For example, "pvd.example.com." or "PvD.Example.coM."
   would refer to the same PvD.

   While resolving names, executing the default address selection
   algorithm [RFC6724] or executing the default router selection
   algorithm when forwarding packets ([RFC2461], ([RFC4861], [RFC4191] and

   [RFC8028]), hosts and applications MAY consider only the
   configuration associated with an arbitrary set of PvDs.

   For example, a host MAY 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.  IoT), or devices with limited CPU or memory resources
   may purposefully use a single PvD while ignoring some received RAs
   containing different PvD IDs.

   The way an application expresses its desire to use a given PvD, or a
   set of PvDs, or the way this selection is enforced, is out of the
   scope of this document.  Useful insights about these considerations
   can be found in [I-D.kline-mif-mpvd-api-reqs].

3.4.1.  DHCPv6 configuration association

   When a host retrieves stateless configuration elements using DHCPv6
   (e.g., DNS recursive resolvers or DNS domain search lists [RFC3646]),
   they MUST be associated with all the explicit and implicit PvDs
   received on the same interface and contained in a RA with the O-flag
   set [RFC4861].

   When a host retrieves stateful assignments using DHCPv6, such
   assignments MUST be associated with the received PvD which 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 2001:db8:cafe::/64, a DHCPv6
   IA_NA message that assigns the address 2001:db8:cafe::1234:4567 would
   be considered to match.

   In cases where an address would be assigned by DHCPv6 and no matching
   PvD could be found, hosts MAY associate the assigned address with any
   implicit PvD received on the same interface or to multiple of
   implicit PvD 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.

3.4.2.  DHCPv4 configuration association

   Associating DHCPv4 [RFC2131] 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 [RFC6146].  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.

   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.

   An Explicit PvD indicates its association with DHCPv4 information by
   setting the L-flag in the PvD RA Option.  If there is exactly one
   Explicit PvD that sets this flag, hosts MUST associate the DHCPv4
   information with that PvD.  Multiple Explicit PvDs on the same
   interface marking this flag is a misconfiguration, and hosts SHOULD
   NOT associate the DHCPv4 information with any Explicit PvD in this
   case.

   If no single Explicit PvD claims association with DHCPv4, the
   configuration elements coming from DHCPv4 MUST be associated with the
   all Implicit PvDs identified by the interface on which the DHCPv4
   transaction happened.  This maintains existing host behavior.

3.4.3.  Connection Sharing by the Host

   The situation when 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 [RFC4389], 64share
   [RFC7278] or prefix delegation (e.g. using DHCPv6-PD [RFC8415]) may
   be used for that purpose.

   Whenever the RAs received from the upstream interface contain a PVD
   RA option, hosts that are sharing connectivity SHOULD include a PVD
   option within the RAs sent downstream with:

   o  The same PVD-ID FQDN

   o  The same H-bit, Delay and Sequence Number values

   o  The L bit set whenever the host is sharing IPv4 connectivity
      received from the same upstream interface

   o  The bits from the Reserved field set to 0

   The values of the R-bit, Router Advertisement message header and
   Options field depend on whether the connectivity should be shared
   only with PvD-aware hosts or not (see Section 3.2).  In particular,
   all options received within the upstream PvD Option and included in
   the downstream RA SHOULD be included in the downstream PvD Option.

3.4.4.  Usage of DNS Servers

   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 Implicit PvD (such as a VPN).
   In all of these cases, the DNS server addresses SHOULD be associated
   with the corresponding PvD.  Specifically, queries sent to a
   configured recursive DNS server SHOULD be sent from a local IP
   address that was provisioned by the PvD via RA or DHCP.  Answers
   received from the DNS server SHOULD only be used on the same PvD.

   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 SHOULD ensure that non-PvD-
   aware name resolution APIs like "getaddrinfo" only use resolvers from
   a single PvD for each query.  More discussion is provided in
   Section 5.2.1 of [RFC7556].

   Maintaining the correct usage of DNS within PvDs avoids various
   practical errors, such as:

   o  A PvD associated with a VPN or otherwise private network may
      provide DNS answers that contain addresses inaccessible over
      another PvD.

   o  A PvD that uses a NAT64 [RFC6146] and DNS64 [RFC6147] 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.

4.  Provisioning Domain Additional Information

   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 [RFC7159]. [RFC8259].
   This JSON object is restricted to the restricted profile of I-JSON,
   as defined in [RFC7493].

   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 MAY 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
   Section 3.4.

   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 Internet of Things (IoT)
   devices.  IoT devices might need only a subset of the information,
   and would in some cases prefer a smaller representation like CBOR
   ([RFC7049]).  Delivering a reduced version of the PvD Additional
   Information designed for such devices is not defined in this
   document.

4.1.  Retrieving the PvD Additional Information

   When the H-flag of the PvD Option is set, hosts MAY attempt to
   retrieve the PvD Additional Information associated with a given PvD
   by performing an HTTP over TLS [RFC2818] GET query to https://<PvD-
   ID>/.well-known/pvd [RFC5785]. [RFC8615].  Inversely, hosts MUST NOT do so
   whenever the H-flag is not set.

   HTTP requests and responses for PvD additional information use the
   "application/pvd+json" media type (see Section 8).  Clients SHOULD
   include this media type as an Accept header in their GET requests,
   and servers MUST mark this media type as their Content-Type header in
   responses.

   Note that the DNS name resolution of the PvD ID, the PKI (Public Key
   Infrastructure) checks as well as the actual query MUST 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 MUST be performed while using exclusively the set of
   configuration information attached with the PvD, as defined in
   Section 3.4.  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.  If the host has a temporary address per
   [RFC4941] in this PvD, then hosts SHOULD use a temporary address to
   fetch the PvD Additional Information and SHOULD deprecate the used
   temporary address and generate a new temporary address afterward.

   If the HTTP status of the answer is greater than or equal to 400 the
   host MUST abandon and consider that there is no additional PvD
   information.  If the HTTP status of the answer is between 300 and
   399, inclusive, it MUST follow the redirection(s).  If the HTTP
   status of the answer is between 200 and 299, inclusive, the host MAY
   get a file containing a single JSON object.

   After retrieval of the PvD Additional Information, hosts MUST
   remember the last Sequence Number value received in the 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 MUST deprecate the
   additional information and stop using it until a new JSON object is
   retrieved.

   Hosts retrieving a new PvD Additional Information object MUST check
   for the presence and validity of the mandatory fields specified in
   Section 4.3.  A retrieved object including an expiration time that is
   already past or missing a mandatory element MUST be ignored.

   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.

   o  When a host performs a JSON object update after it detected a
      change in the PvD Option Sequence Number, it MUST add a delay
      before sending the query.  The target time for the delay is
      calculated as a random time between zero and 2**(Delay * 2)
      milliseconds, where 'Delay' corresponds to the 4-bit unsigned
      integer in the last received PvD Option.

   o  When a host last retrieved a JSON object at time A that includes a
      expiry time B using the "expires" key, and the host is configured
      to keep the PvD information up to date, it MUST 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].

   In the example Figure 2, the delay field value is 5, this means that
   host calculates its delay by choosing a random number between 0 and
   2**(5 * 2) milliseconds, i.e., between 0 and 1024 milliseconds.

   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 value while changing the Delay value
   depending on the criticality of the update and its PvD Additional
   Information servers capacity.

   The PvD Additional Information object includes a set of IPv6 prefixes
   (under the key "prefixes") which MUST be checked against all the
   Prefix Information Options advertised in the RA.  If any of the
   prefixes included in the PIO is not covered by at least one of the
   listed prefixes, the associated PvD information MUST be considered to
   be a misconfiguration, and MUST NOT be used by the host.  See
   Section 4.4 for more discussion on handling such misconfigurations.

4.2.  Operational Consideration to Providing the PvD Additional
      Information

   Whenever the H-flag is set in the PvD Option, a valid PvD Additional
   Information object MUST be made available to all hosts receiving the
   RA by the network operator.  In particular, when a captive portal is
   present, hosts MUST still be allowed to perform DNS, PKI and HTTP
   over TLS operations related to the retrieval of the object, even
   before logging into the captive portal.

   Routers SHOULD 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 SHOULD wrap back to zero.

   The server providing the JSON files SHOULD also check whether the
   client address is part of the prefixes listed into the additional
   information and SHOULD return a 403 response code if there is no
   match.

4.3.  PvD Additional Information Format

   The PvD Additional Information is a JSON object.

   The following table presents the mandatory keys which MUST be
   included in the object:

   +------------+-----------------+-----------+------------------------+
   | JSON key   | Description     | Type      | Example                |
   +------------+-----------------+-----------+------------------------+
   | identifier | PvD ID FQDN     | String    | "pvd.example.com."     |
   |            |                 |           |                        |
   | expires    | Date after      | [RFC3339] | "2017-07-23T06:00:00Z" |
   |            | which this      | Date      |                        |
   |            | object is no    |           |                        |
   |            | longer valid    |           |                        |
   |            |                 |           |                        |
   | prefixes   | Array of IPv6   | Array of  | ["2001:db8:1::/48",    |
   |            | prefixes valid  | strings   | "2001:db8:4::/48"]     |
   |            | for this PvD    |           |                        |
   +------------+-----------------+-----------+------------------------+

   A retrieved object which does not include all three of these keys at
   the root of the JSON object MUST be ignored.  All three keys need to
   be validated, otherwise the object MUST be ignored.  The value stored
   for "identifier" MUST be matched against the PvD ID FQDN presented in
   the PvD RA option using the comparison mechanism described in
   Section 3.4.  The value stored for "expires" MUST 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 SHOULD be ignored.

   The following table presents some optional keys which MAY be included
   in the object.

   +------------+----------------------+----------+--------------------+
   | JSON key   | Description          | Type     | Example            |
   +------------+----------------------+----------+--------------------+
   | dnsZones   | DNS zones searchable | Array of | ["example.com",    |
   |            | and accessible       | strings  |                    |
   |            |                      |          |                    |
   |            |                      |          | "sub.example.com"] |
   |            |                      |          |                    |
   | noInternet | No Internet, set     | Boolean  | true               |
   |            | when the PvD is      |          |                    |
   |            | restricted.          |          |                    |
   +------------+----------------------+----------+--------------------+

   It is worth noting that the JSON format allows for extensions.
   Whenever an unknown key is encountered, it MUST be ignored along with
   its associated elements.

   Private-use or experimental keys MAY be used in the JSON dictionary.
   In order to avoid such keys colliding with IANA registry keys,
   implementers or vendors defining private-use or experimental keys
   MUST create sub-dictionaries, where the sub-dictionary is added into
   the top-level JSON dictionary with a key of the format "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".  Upon receiving such a sub-dictionary,
   host MUST ignore this sub-dictionary if it is unknown.  When the
   vendor or implementer is part of an IANA URN namespace [URN], the URN
   namespace SHOULD be used rather than the "vendor-*" format.

4.3.1.  Example

   The following two examples show how the JSON keys defined in this
   document can be used:

   {
     "identifier": "cafe.example.com",
     "expires": "2017-07-23T06:00:00Z",
     "prefixes": ["2001:db8:1::/48", "2001:db8:4::/48"],
   }

   {
     "identifier": "company.foo.example.com",
     "expires": "2017-07-23T06:00:00Z",
     "prefixes": ["2001:db8:1::/48", "2001:db8:4::/48"],
     "vendor-foo": { "private-key": "private-value" },
   }

4.4.  Detecting misconfiguration and misuse

   When a host retrieves the PvD Additional Information, it MUST verify
   that the TLS server certificate is valid for the performed request
   (e.g., that the Subject Name is equal to the PvD ID expressed as an
   FQDN).  This authentication creates a secure binding between the
   information provided by the trusted Router Advertisement, and the
   HTTPS server.  However, this does not mean the Advertising Router and
   the PvD server belong to the same entity.

   Hosts MUST verify that all prefixes in the RA PIO 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 NAT66 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.

   If NAT66 is being added in order to spoof PvD ownership, the HTTPS
   server for additional information can detect this misconfiguration.
   The HTTPS server SHOULD validate the source addresses of incoming
   connections (see Section 4.1).  This check gives reasonable assurance
   that neither NPTv6 [RFC6296] nor NAT66 were used and restricts the
   information to the valid network users.  If the PvD does not
   provision IPv4 (it does not include the 'L' bit in the RA), the
   server cannot validate the source addresses of connections using
   IPv4.  Thus, the PvD ID FQDN for such PvDs SHOULD NOT have a DNS A
   record.

5.  Operational Considerations

   This section describes some example use cases of PvD.  For the sake
   of simplicity, the RA messages will not be described in the usual
   ASCII art but rather in an indented list.

5.1.  Exposing Extra RA Options to PvD-Aware Hosts

   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.

   o  RA Header: router lifetime = 6000

   o  Prefix Information Option: length = 4, prefix = 2001:db8:cafe::/64

   o  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)

      *  Recursive DNS Server: length = 5, addresses =
         [2001:db8:cafe::53, 2001:db8:f00d::53]

      *  Prefix Information Option: length = 4, prefix =
         2001:db8:f00d::/64

   Note that a PvD-aware host will receive two different prefixes,
   2001:db8:cafe::/64 and 2001:db8:f00d::/64, both associated with the
   same PvD (identified by "example.org.").  A non-PvD-aware host will
   only receive one prefix, 2001:db8:cafe::/64.

5.2.  Different RAs for PvD-Aware and Non-PvD-Aware Hosts

   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 recommended to send two RA messages (one for each class of hosts).
   For example, here is the RA sent for non-PvD-aware hosts:

   o  RA Header: router lifetime = 6000 (non-PvD-aware hosts will use
      this router as a default router)

   o  Prefix Information Option: length = 4, prefix = 2001:db8:cafe::/64

   o  Recursive DNS Server Option: length = 3, addresses=
      [2001:db8:cafe::53]

   o  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)

      *  RA Header: router lifetime = 0 (PvD-aware hosts will not use
         this router as a default router), implicit length = 2

   And here is the RA sent for PvD-aware hosts:

   o  RA Header: router lifetime = 0 (non-PvD-aware hosts will not use
      this router as a default router)

   o  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)

      *  RA Header: router lifetime = 1600 (PvD-aware hosts will use
         this router as a default router), implicit length = 2

      *  Prefix Information Option: length = 4, prefix =
         2001:db8:f00d::/64

      *  Recursive DNS Server Option: length = 3, addresses =
         [2001:db8:f00d::53]

   In the above example, non-PvD-aware hosts will only use the first RA
   sent from their default router and using the 2001:db8:cafe::/64
   prefix.  PvD-aware hosts will autonomously configure addresses from
   both PIOs, but will only use the source address in 2001:db8:f00d::/64
   to communicate past the first hop router since only the router
   sending the second RA will be used as default router; similarly, they
   will use the DNS server 2001:db8:f00d::53 when communicating with
   this address.

5.3.  Enabling Multi-homing for PvD-Aware Hosts

   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 multi-home on the network.

   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.

   o  RA Header: router lifetime = 6000 (non-PvD-aware hosts will use
      this router as a default router)

   o  Prefix Information Option: length = 4, prefix = 2001:db8:cafe::/64

   o  Recursive DNS Server Option: length = 3, addresses=
      [2001:db8:cafe::53]

   o  PvD Option header: length = 3, PvD ID FQDN = foo.example.org.,
      R-flag = 0 (actual length of the header 24 bytes = 3 * 8 bytes)

   The second RA contains a prefix usable only by PvD-aware hosts.  Non-
   PvD-aware hosts will ignore this RA.

   o  RA Header: router lifetime = 0 (non-PvD-aware hosts will not use
      this router as a default router)

   o  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)

      *  RA Header: router lifetime = 1600 (PvD-aware hosts will use
         this router as a default router), implicit length = 2

      *  Prefix Information Option: length = 4, prefix =
         2001:db8:f00d::/64

      *  Recursive DNS Server Option: length = 3, addresses =
         [2001:db8:f00d::53]

6.  Security Considerations

   Although some solutions such as IPsec or SeND [RFC3971] 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 [IEEE8021X]) in conjunction with RA
   Guard [RFC6105].

   This specification does not improve the Neighbor Discovery Protocol
   security model, but extends the purely link-local trust relationship
   between the host and the default routers with HTTP over TLS
   communications which servers are authenticated as rightful owners of
   the FQDN received within the trusted PvD ID RA option.

   It must be noted that Section 4.4 of this document only provides
   reasonable assurance against misconfiguration but does not prevent an
   hostile network access provider to advertise wrong information that
   could lead applications or hosts to select a hostile PvD.

   Users cannot be assumed to be able to meaningfully differentiate
   between "safe" and "unsafe" networks.  This is a known attack surface
   that is present whether or not PvDs are in use, and hence cannot be
   addressed by this document.  However, a host that correctly
   implements the MPvD architecture ([RFC7556]) using the mechanism
   described in this document will be less susceptible to such attacks
   than a host that does not by being able to check for the various
   misconfigurations described in this document.

7.  Privacy Considerations

   Retrieval of the PvD Additional Information over HTTPS requires early
   communications between the connecting host and a server which 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.  Therefore, hosts
   willing to retrieve the PvD Additional Information before using it
   without leaking identity information, SHOULD make use of an IPv6
   Privacy Address and SHOULD NOT include any privacy sensitive data,
   such as User Agent header or HTTP cookie, while performing the HTTP
   over TLS query.

   From a 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 well known web
   sites, such as http://captive.example.com/hotspot-detect.html, in
   order to detect the presence of a captive portal.

   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 a
   whitelist of 'trusted' FQDNs and/or IP prefixes that the host is
   allowed to communicate with.  In such scenarios, the host SHOULD
   check that the provided PvD ID, as well as the IP address that it
   resolves into, are part of the allowed whitelist.

8.  IANA Considerations

   Upon publication of this document, IANA is asked to remove the
   'reclaimable' tag off the value 21 for the PvD Option (from the IPv6
   Neighbor Discovery Option Formats registry).

   IANA is asked to assign the value "pvd" from the Well-Known URIs
   registry.

8.1.  Additional Information PvD Keys Registry

   IANA is asked to create and maintain a new registry called
   "Additional Information PvD Keys", which will reserve JSON keys for
   use in PvD additional information.  The initial contents of this
   registry are given in Section 4.3.

   New assignments for Additional Information PvD Keys Registry will be
   administered by IANA through Expert Review [RFC8126].

8.2.  PvD Option Flags Registry

   IANA is also asked to create and maintain a new registry entitled
   "PvD Option Flags" reserving bit positions from 0 to 15 to be used in
   the PvD Option bitmask.  Bit position 0, 1 and 2 are reserved by this
   document (as specified in Figure 1).  Future assignments require
   Standards Action [RFC8126], via a Standards Track RFC document.

8.3.  PvD JSON Media Type Registration

   This document registers the media type for PvD JSON text,
   "application/pvd+json".

   Type Name: application

   Subtype Name: pvd+json

   Required parameters: None

   Optional parameters: None

   Encoding considerations: Encoding considerations are identical to
   those specified for the "application/json" media type.

   Security considerations: See Section 6.

   Interoperability considerations: This document specifies format of
   conforming messages and the interpretation thereof.

   Published specification: This document

   Applications that use this media type: This media type is intended to
   be used by network advertising additional Provisioning Domain
   information, and clients looking up such information.

   Additional information: None

   Person and email address to contact for further information: See
   Authors' Addresses section

   Intended usage: COMMON

   Restrictions on usage: None

   Author: IETF

   Change controller: IETF

9.  Acknowledgments

   Many thanks to M.  Stenberg and S.  Barth for their earlier work:
   [I-D.stenberg-mif-mpvd-dns], as well as to Basile Bruneau who was
   author of an early version of this document.

   Thanks also to Marcus Keane, Mikael Abrahamsson, Ray Bellis, Zhen
   Cao, Tim Chown, Lorenzo Colitti, Michael Di Bartolomeo, Ian Farrer,
   Phillip Hallam-Baker, Bob Hinden, Tatuya Jinmei, Erik Kline, Ted
   Lemon, Paul Hoffman, Dave Thaler, Suresh Krishnan, Gorry Fairhurst,
   Jen Lenkova, Veronika McKillop, Mark Townsley and James Woodyatt for
   useful and interesting discussions and reviews.

   Finally, special thanks to Thierry Danis and Wenqin Shao for their
   valuable inputs and implementation efforts, Tom Jones for his
   integration effort into the NEAT project and Rigil Salim for his
   implementation work.

10.  References

10.1.  Normative References

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
              November 1987, <https://www.rfc-editor.org/info/rfc1035>.

   [RFC2461]  Narten, T., Nordmark, E., and W. Simpson, "Neighbor
              Discovery for IP Version 6 (IPv6)", RFC 2461,
              DOI 10.17487/RFC2461, December 1998,
              <https://www.rfc-editor.org/info/rfc2461>.

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818,
              DOI 10.17487/RFC2818, May 2000,
              <https://www.rfc-editor.org/info/rfc2818>.

   [RFC3646]  Droms, R., Ed., "DNS Configuration options for Dynamic
              Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3646,
              DOI 10.17487/RFC3646, December 2003,
              <https://www.rfc-editor.org/info/rfc3646>.

   [RFC4343]  Eastlake 3rd, D., "Domain Name System (DNS) Case
              Insensitivity Clarification", RFC 4343,
              DOI 10.17487/RFC4343, January 2006,
              <https://www.rfc-editor.org/info/rfc4343>.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              DOI 10.17487/RFC4861, September 2007,
              <https://www.rfc-editor.org/info/rfc4861>.

   [RFC7159]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
              2014, <https://www.rfc-editor.org/info/rfc7159>.

   [RFC7493]  Bray, T., Ed., "The I-JSON Message Format", RFC 7493,
              DOI 10.17487/RFC7493, March 2015,
              <https://www.rfc-editor.org/info/rfc7493>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [RFC8259]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", STD 90, RFC 8259,
              DOI 10.17487/RFC8259, December 2017,
              <https://www.rfc-editor.org/info/rfc8259>.

   [RFC8615]  Nottingham, M., "Well-Known Uniform Resource Identifiers
              (URIs)", RFC 8615, DOI 10.17487/RFC8615, May 2019,
              <https://www.rfc-editor.org/info/rfc8615>.

10.2.  Informative References

   [I-D.kline-mif-mpvd-api-reqs]
              Kline, E., "Multiple Provisioning Domains API
              Requirements", draft-kline-mif-mpvd-api-reqs-00 (work in
              progress), November 2015.

   [I-D.stenberg-mif-mpvd-dns]
              Stenberg, M. and S. Barth, "Multiple Provisioning Domains
              using Domain Name System", draft-stenberg-mif-mpvd-dns-00
              (work in progress), October 2015.

   [IEEE8021X]
              "IEEE Standards for Local and Metropolitan Area Networks,
              Port-based Network Access Control, IEEE Std", n.d..

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, DOI 10.17487/RFC2131, March 1997,
              <https://www.rfc-editor.org/info/rfc2131>.

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818,
              DOI 10.17487/RFC2818, May 2000,
              <https://www.rfc-editor.org/info/rfc2818>.

   [RFC3339]  Klyne, G. and C. Newman, "Date and Time on the Internet:
              Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
              <https://www.rfc-editor.org/info/rfc3339>.

   [RFC3971]  Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
              "SEcure Neighbor Discovery (SEND)", RFC 3971,
              DOI 10.17487/RFC3971, March 2005,
              <https://www.rfc-editor.org/info/rfc3971>.

   [RFC4191]  Draves, R. and D. Thaler, "Default Router Preferences and
              More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191,
              November 2005, <https://www.rfc-editor.org/info/rfc4191>.

   [RFC4389]  Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery
              Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April
              2006, <https://www.rfc-editor.org/info/rfc4389>.

   [RFC4941]  Narten, T., Draves, R., and S. Krishnan, "Privacy
              Extensions for Stateless Address Autoconfiguration in
              IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007,
              <https://www.rfc-editor.org/info/rfc4941>.

   [RFC5785]  Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known
              Uniform Resource Identifiers (URIs)", RFC 5785,
              DOI 10.17487/RFC5785, April 2010,
              <https://www.rfc-editor.org/info/rfc5785>.

   [RFC6105]  Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J.
              Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105,
              DOI 10.17487/RFC6105, February 2011,
              <https://www.rfc-editor.org/info/rfc6105>.

   [RFC6146]  Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
              NAT64: Network Address and Protocol Translation from IPv6
              Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146,
              April 2011, <https://www.rfc-editor.org/info/rfc6146>.

   [RFC6147]  Bagnulo, M., Sullivan, A., Matthews, P., and I. van
              Beijnum, "DNS64: DNS Extensions for Network Address
              Translation from IPv6 Clients to IPv4 Servers", RFC 6147,
              DOI 10.17487/RFC6147, April 2011,
              <https://www.rfc-editor.org/info/rfc6147>.

   [RFC6296]  Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network Prefix
              Translation", RFC 6296, DOI 10.17487/RFC6296, June 2011,
              <https://www.rfc-editor.org/info/rfc6296>.

   [RFC6724]  Thaler, D., Ed., Draves, R., Matsumoto, A., and T. Chown,
              "Default Address Selection for Internet Protocol Version 6
              (IPv6)", RFC 6724, DOI 10.17487/RFC6724, September 2012,
              <https://www.rfc-editor.org/info/rfc6724>.

   [RFC7049]  Bormann, C. and P. Hoffman, "Concise Binary Object
              Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
              October 2013, <https://www.rfc-editor.org/info/rfc7049>.

   [RFC7278]  Byrne, C., Drown, D., and A. Vizdal, "Extending an IPv6
              /64 Prefix from a Third Generation Partnership Project
              (3GPP) Mobile Interface to a LAN Link", RFC 7278,
              DOI 10.17487/RFC7278, June 2014,
              <https://www.rfc-editor.org/info/rfc7278>.

   [RFC7556]  Anipko, D., Ed., "Multiple Provisioning Domain
              Architecture", RFC 7556, DOI 10.17487/RFC7556, June 2015,
              <https://www.rfc-editor.org/info/rfc7556>.

   [RFC8028]  Baker, F. and B. Carpenter, "First-Hop Router Selection by
              Hosts in a Multi-Prefix Network", RFC 8028,
              DOI 10.17487/RFC8028, November 2016,
              <https://www.rfc-editor.org/info/rfc8028>.

   [RFC8106]  Jeong, J., Park, S., Beloeil, L., and S. Madanapalli,
              "IPv6 Router Advertisement Options for DNS Configuration",
              RFC 8106, DOI 10.17487/RFC8106, March 2017,
              <https://www.rfc-editor.org/info/rfc8106>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8415]  Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
              Richardson, M., Jiang, S., Lemon, T., and T. Winters,
              "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
              RFC 8415, DOI 10.17487/RFC8415, November 2018,
              <https://www.rfc-editor.org/info/rfc8415>.

   [URN]      "URN Namespaces", n.d..

Authors' Addresses
   Pierre Pfister
   Cisco
   11 Rue Camille Desmoulins
   Issy-les-Moulineaux 92130
   France

   Email: ppfister@cisco.com

   Eric Vyncke
   Cisco
   De Kleetlaan, 6
   Diegem 1831
   Belgium

   Email: evyncke@cisco.com

   Tommy Pauly
   Apple Inc.
   One Apple Park Way
   Cupertino, California 95014
   United States of America

   Email: tpauly@apple.com

   David Schinazi
   Google LLC
   1600 Amphitheatre Parkway
   Mountain View, California 94043
   United States of America

   Email: dschinazi.ietf@gmail.com

   Wenqin Shao
   Cisco
   11 Rue Camille Desmoulins
   Issy-les-Moulineaux 92130
   France

   Email: wenshao@apple.com wenshao@cisco.com