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Discovering Provisioning Domain Names and Data
draft-ietf-intarea-provisioning-domains-11

The information below is for an old version of the document that is already published as an RFC.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 8801.
Authors Pierre Pfister , Éric Vyncke , Tommy Pauly , David Schinazi , Wenqin Shao
Last updated 2020-07-29 (Latest revision 2020-01-31)
Replaces draft-bruneau-intarea-provisioning-domains
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status Proposed Standard
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Stream WG state Submitted to IESG for Publication
Document shepherd Erik Kline
Shepherd write-up Show Last changed 2019-10-06
IESG IESG state Became RFC 8801 (Proposed Standard)
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Consensus boilerplate Yes
Telechat date (None)
Responsible AD Suresh Krishnan
Send notices to Erik Kline <ek@loon.com>
IANA IANA review state Version Changed - Review Needed
IANA action state RFC-Ed-Ack
IANA expert review state Expert Reviews OK
draft-ietf-intarea-provisioning-domains-11
Network Working Group                                         P. Pfister
Internet-Draft                                                 E. Vyncke
Intended status: Standards Track                                   Cisco
Expires: August 3, 2020                                         T. Pauly
                                                              Apple Inc.
                                                             D. Schinazi
                                                              Google LLC
                                                                 W. Shao
                                                                   Cisco
                                                        January 31, 2020

             Discovering Provisioning Domain Names and Data
               draft-ietf-intarea-provisioning-domains-11

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 August 3, 2020.

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Copyright Notice

   Copyright (c) 2020 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  . . . . . . . . . .  11
       3.4.3.  Connection Sharing by the Host  . . . . . . . . . . .  11
       3.4.4.  Usage of DNS Servers  . . . . . . . . . . . . . . . .  12
   4.  Provisioning Domain Additional Information  . . . . . . . . .  13
     4.1.  Retrieving the PvD Additional Information . . . . . . . .  13
     4.2.  Operational Consideration to Providing the PvD Additional
           Information . . . . . . . . . . . . . . . . . . . . . . .  16
     4.3.  PvD Additional Information Format . . . . . . . . . . . .  16
       4.3.1.  Example . . . . . . . . . . . . . . . . . . . . . . .  18
     4.4.  Detecting misconfiguration and misuse . . . . . . . . . .  18
   5.  Operational Considerations  . . . . . . . . . . . . . . . . .  19
     5.1.  Exposing Extra RA Options to PvD-Aware Hosts  . . . . . .  19
     5.2.  Different RAs for PvD-Aware and Non-PvD-Aware Hosts . . .  19
     5.3.  Enabling Multi-homing for PvD-Aware Hosts . . . . . . . .  21
     5.4.  Providing Additional Information to PvD-Aware Hosts . . .  22
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  23
   7.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  24
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  25
     8.1.  New entry in the Well-Known URIs Registry . . . . . . . .  26
     8.2.  Additional Information PvD Keys Registry  . . . . . . . .  26
     8.3.  PvD Option Flags Registry . . . . . . . . . . . . . . . .  26

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     8.4.  PvD JSON Media Type Registration  . . . . . . . . . . . .  27
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  28
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  28
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  28
     10.2.  Informative References . . . . . . . . . . . . . . . . .  30
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  32

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 information 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,
   derived from it.  The PVD ID Router Advertisement option may also
   contain a set of other RA options, along with an optional inner
   Router Advertisement message header.  These options and optional

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   inner header are only visible to 'PvD-aware' hosts, allowing such
   hosts to have a specialized view of the network configuration.

   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 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.

   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].

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   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) that identifies the network operator.
   Network operators MUST use names that they own or manage to avoid
   naming conflicts.  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
   the 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.

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    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 PvD is associated
      with IPv4 information assigned using DHCPv4 (see Section 3.4.2).

   R-flag:  (1 bit) 'Router Advertisement' flag stating whether the PvD
      Option header is followed (right after padding to the next 64 bits
      boundary) by a Router Advertisement message header (see section
      4.2 of [RFC4861]).  The usage of the inner message header is
      described in Section 3.4.

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

   Delay:  (4 bits) Unsigned integer used to delay HTTP GET queries from
      hosts by a randomized backoff (see Section 4.1).  If the H-flag is
      not set, senders SHOULD set the delay to zero, and receivers
      SHOULD ignore the value.

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   Sequence Number:  (16 bits) Sequence number for the PvD Additional
      Information, as described in Section 4.  If the H-flag is not set,
      senders SHOULD set the Sequence Number to zero, and receivers
      SHOULD ignore the value.

   PvD ID FQDN:  The FQDN used as PvD ID encoded in DNS format, as
      described in Section 3.1 of [RFC1035].  Domain name 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 without
      causing the processing of the message to fail.  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 so as to be ignored by hosts that are
      not PvD-aware.

   Figure 2 shows an example of a PvD Option with "example.org" as the
   PvD ID FQDN and including both a Recursive DNS Server (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 1.

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    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              ...
   ...                                                             |
   ...                                                             |
   +---------------------------------------------------------------+

                                 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 as per
   section 4.2 of [RFC4861].

   In order to provide multiple different PvDs, a router MUST send
   multiple RAs.  RAs sent from different link-local source addresses
   establish distinct implicit PvDs, in the absence of a PvD Option.
   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.  If a link-local address on the router is

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   changed, then any new RA will be interpreted as a different Implicit
   PvD by PvD-aware hosts.

   As specified in [RFC4861] and [RFC6980], when the set of options
   causes the size of an advertisement to exceed the link MTU, multiple
   router advertisements MUST 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) 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 ensures the backward compatibility
   required in Section 3.3 of [RFC7556].  This behavior allows for a
   mixed-mode network where 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.  If an RA message header is present both
   within the PvD Option and outside it, the header within the PvD
   Option takes precedence.

   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 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 which included the given PIO.

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   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 performing PvD-specific operations such as resolving names,
   executing the default address selection algorithm [RFC6724] or
   executing the default router selection algorithm when forwarding
   packets ([RFC4861], [RFC4191] and [RFC8028]), hosts and applications
   MAY consider only the configuration associated with any non-empty
   subset 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 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.

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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 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-flag, Delay and Sequence Number values

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   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-flag, 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 Explicit PvD (such as a VPN).
   In all of these cases, the recursive 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 for 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 a given query.  Handling DNS across PvDs is
   discussed in Section 5.2.1 of [RFC7556], and PvD APIs are discussed
   in Section 6 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.  This includes the DNS queries to retrieve PvD
      additional information, which could otherwise send identifying
      information to the recursive DNS system (see Section 4.1).

   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.

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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 [RFC8259].
   This JSON object is restricted to the I-JSON profile, 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.  Inversely, hosts MUST NOT do so whenever the
   H-flag is not set.

   Recommendations for how to use TLS securely can be found in
   [RFC7525].

   When a host retrieves the PvD Additional Information, it MUST verify
   that the TLS server certificate is valid for the performed request;
   specifically, that a DNS-ID [RFC6125] 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

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   the router.  If this validation fails, hosts MUST close the
   connection and treat the PvD as if it has no Additional Information.

   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 field in their GET
   requests, and servers MUST mark this media type as their Content-Type
   header field in responses.

   Note that the DNS name resolution of the PvD ID, any connections made
   for certficate validation (such as OCSP [RFC6960]), and the HTTP
   request itself 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.  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 [RFC4941] in this PvD, then it SHOULD use a temporary
   address to fetch the PvD Additional Information and MAY 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 close its connection 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 response is expected to be a single JSON object.

   After retrieval of the PvD Additional Information, hosts MUST
   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 MUST deprecate the
   additional information and stop using it.

   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.

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   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**(10 + Delay)
      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 1, this means that
   the host calculates its delay by choosing a uniformly random time
   between 0 and 2**(10 + 1) milliseconds, i.e., between 0 and 2048
   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 Number value while changing the Delay value
   depending on the criticality of the update and its PvD Additional
   Information servers capacity.

   In addition to adding a random delay when fetching Additional
   Information, hosts MUST enforce a minimum time between requesting
   Additional Information for a given PvD on the same network.  This
   minimum time is RECOMMENDED to be 10 seconds, in order to avoid hosts
   causing a denial-of-service on the PvD server.  Hosts also MUST 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 RECOMMENDED 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 Section 6.

   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 any associated 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.

   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 MUST close any connection

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   used to fetch the PvD Additional Information, and MUST NOT 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 MUST NOT 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 Section 6.

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, certficate
   validation, 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 MUST wrap back to zero.

   The server providing the JSON files SHOULD also check whether the
   client address is contained by the prefixes listed in 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:

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   +------------+-----------------+-----------+------------------------+
   | JSON key   | Description     | Type      | Example                |
   +------------+-----------------+-----------+------------------------+
   | identifier | PvD ID FQDN     | String    | "pvd.example.com."     |
   |            |                 |           |                        |
   | expires    | Date after      | [RFC3339] | "2020-05-23T06:00:00Z" |
   |            | 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   | ["example.com",    |
   |            | and accessible        | of      | "sub.example.com"] |
   |            |                       | strings |                    |
   |            |                       |         |                    |
   | noInternet | No Internet, set to   | Boolean | true               |
   |            | "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

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   MUST create sub-dictionaries.  If a set of PvD Additional Information
   keys are defined by an organization that has a Formal URN Namespace
   [URN], the URN namespace SHOULD be used as the top-level JSON key for
   the sub-dictionary.  For other private uses, the sub-dictionary key
   SHOULD 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 MUST ignore
   the contents of the sub-dictionary.

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": "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",
       },
   }

4.4.  Detecting misconfiguration and misuse

   Hosts MUST validate the TLS server certificate when retrieving PvD
   Additional Information, as detailed in Section 4.1.

   Hosts MUST 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 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

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   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 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).

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.
   This approach allows for two distinct sets of configuration

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   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.

   If two RA messages are sent for this reason, they MUST be sent from
   two different link-local source addresses (Section 3.2).  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
   listed RA sent by 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 from this address.

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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; hence, the only PvD-aware hosts
   will be multi-homed.

   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]

   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.

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5.4.  Providing Additional Information to PvD-Aware Hosts

   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.

   o  RA Header: router lifetime = 6000

   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 = cafe.example.com.,
      Sequence Number = 7, R-flag = 0, H-flag = 1 (actual length of the
      header with padding 24 bytes = 3 * 8 bytes)

   A PvD-aware host will fetch https://cafe.example.com/.well-known/pvd
   to get the additonal information.  The following example shows a GET
   request that the host sends, in HTTP/2 syntax [RFC7540]:

   :method = GET
   :scheme = https
   :authority = cafe.example.com
   :path = /.well-known/pvd
   accept = application/pvd+json

   The HTTP server will respond with the JSON additional information:

   :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"],
   }

   At this point, the host has the 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.

   For example, if the router sends a new RA with the Sequence Number
   set to 8, the host will re-fetch the additional information:

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   o  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)

   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).

6.  Security Considerations

   Since the PvD ID RA 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 ID option.

   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].

   If multiple RAs are sent for a single PvD to avoid fragmentation,
   dropping packets can lead to processing only part of a PvD ID option,
   which could lead to hosts receiving only part of the contained
   options.  As discussed in Section 3.2, routers MUST include the PvD
   ID option in all fragments generated.

   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.

   It must be noted that Section 4.4 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 ([RFC7556]) 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.

   Since expiration times provided in PvD Additional Information use
   absolute time, these values can be skewed for hosts without an

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   accurate time base, or due to clock skew.  Such time values MUST NOT
   be used for security-sensitive functionality or decisions.

   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 MUST:

   o  limit the rate at which they fetch a particular PvD's Additional
      Information;

   o  limit the rate at which they fetch any PvD Additional Information
      on a given local network;

   o  stop making requests for a PvD ID that does not respond with valid
      JSON;

   o  stop making requests for all PvD IDs once a certain number of
      failures is reached on a particular network.

   Details are provided in Section 4.1.  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 SHOULD reject any requests that do not
   originate from the expected IPv6 prefix as described in Section 4.2.

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.  To minimize the
   leakage of identity information while retrieving the PvD Additional
   Information, hosts SHOULD make use of an IPv6 temporary address and
   SHOULD NOT include any privacy-sensitive data, such as a User-Agent
   header field or an HTTP cookie.

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   Hosts might not always fetch PvD Additional Information, depending on
   whether or not they expect to use the information.  However, if a
   host whitelisted only certain PvD IDs for which to fetch Additional
   Information, an attacker could send various PvD IDs in RAs to detect
   which PvD IDs are whitelisted by the client.  To avoid this, hosts
   SHOULD either fetch Additional Information for all eligible PvD IDs
   on a given local network, or fetch the information for none of them.

   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 http://captive.example.com/hotspot-
   detect.html, in order to detect the presence of a captive portal.

   The DNS queries associated with the PvD Additional Information MUST
   use the DNS servers indicated by the associated PvD, as described in
   Section 4.1.  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.

   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.

   Network operators SHOULD 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 whitelisting 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 Section 4.2.

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).

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8.1.  New entry in the Well-Known URIs Registry

   IANA is asked to add a new entry in the Well-Known URIs registry
   [RFC8615] with the following information:

   URI suffix: 'pvd'

   Change controller: IETF

   Specification document: this document

   Status: permanent

   Related information: N/A

8.2.  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, including both the table of
   mandatory keys and the table of optional keys.

   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.

   New assignments for Additional Information PvD Keys Registry will be
   administered by IANA through Expert Review [RFC8126].  Experts are
   requested to ensure that defined keys do not overlap in names or
   semantics, and represent non-vendor-specific use cases.  Vendor-
   specific keys SHOULD use sub-dictionaries, as described in
   Section 4.3.

   IANA is asked to place this registry in a new page, entitled
   "Provisioning Domains (PvDs)".

8.3.  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 12 to be used in
   the PvD Option bitmask.  Bit position 0, 1 and 2 are assigned by this
   document (as specified in Figure 1).  Future assignments require
   Standards Action [RFC8126].

   Since these flags apply to an IPv6 Router Advertisement Option, IANA
   is asked to place this registry under the existing "Internet Control

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   Message Protocol version 6 (ICMPv6) Parameters" page, as well as
   providing a link on the new "Provisioning Domains (PvDs)" page.

8.4.  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: N/A

   Optional parameters: N/A

   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 the 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 networks advertising additional Provisioning Domain
   information, and clients looking up such information.

   Fragment identifier considerations: N/A

   Additional information: N/A

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

   Intended usage: COMMON

   Restrictions on usage: N/A

   Author: IETF

   Change controller: IETF

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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 for his 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>.

   [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>.

   [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>.

   [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>.

   [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>.

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   [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>.

   [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>.

   [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>.

   [RFC6980]  Gont, F., "Security Implications of IPv6 Fragmentation
              with IPv6 Neighbor Discovery", RFC 6980,
              DOI 10.17487/RFC6980, August 2013,
              <https://www.rfc-editor.org/info/rfc6980>.

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

   [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
              2015, <https://www.rfc-editor.org/info/rfc7525>.

   [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>.

   [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>.

   [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>.

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

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

   [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>.

   [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>.

   [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>.

   [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>.

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   [RFC6125]  Saint-Andre, P. and J. Hodges, "Representation and
              Verification of Domain-Based Application Service Identity
              within Internet Public Key Infrastructure Using X.509
              (PKIX) Certificates in the Context of Transport Layer
              Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
              2011, <https://www.rfc-editor.org/info/rfc6125>.

   [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>.

   [RFC6960]  Santesson, S., Myers, M., Ankney, R., Malpani, A.,
              Galperin, S., and C. Adams, "X.509 Internet Public Key
              Infrastructure Online Certificate Status Protocol - OCSP",
              RFC 6960, DOI 10.17487/RFC6960, June 2013,
              <https://www.rfc-editor.org/info/rfc6960>.

   [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>.

   [RFC7540]  Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
              Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
              DOI 10.17487/RFC7540, May 2015,
              <https://www.rfc-editor.org/info/rfc7540>.

   [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>.

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   [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]      IANA, "Uniform Resource Names (URN) Namespaces",
              <https://www.iana.org/assignments/urn-namespaces/
              urn-namespaces.xhtml>.

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

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

   Email: wenshao@cisco.com

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