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Versions: (draft-pref64folks-6man-ra-pref64) 00 01 02 03 04

IPv6 Maintenance                                              L. Colitti
Internet-Draft                                                  E. Kline
Intended status: Standards Track                              J. Linkova
Expires: September 25, 2019                                       Google
                                                          March 24, 2019


              Discovering PREF64 in Router Advertisements
                      draft-ietf-6man-ra-pref64-00

Abstract

   This document specifies a Router Advertisement option to communicate
   NAT64 prefixes to clients.

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
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 25, 2019.

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
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.





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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   2
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Use cases for communicating the NAT64 prefix to hosts . . . .   3
   3.  Why include the NAT64 prefix in Router Advertisements . . . .   3
   4.  Semantics . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Option format . . . . . . . . . . . . . . . . . . . . . . . .   4
   6.  Handling Multiple NAT64 Prefixes  . . . . . . . . . . . . . .   5
   7.  Multihoming . . . . . . . . . . . . . . . . . . . . . . . . .   6
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     11.1.  Normative References . . . . . . . . . . . . . . . . . .   7
     11.2.  Informative References . . . . . . . . . . . . . . . . .   8
     11.3.  URIs . . . . . . . . . . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   NAT64 [RFC6146] with DNS64 [RFC6147] is a widely-deployed mechanism
   to provide IPv4 access on IPv6-only networks.  In various scenarios,
   the host must be aware of the NAT64 prefix in use by the network.
   This document specifies a Router Advertisement [RFC4861] option to
   communicate the NAT64 prefix to hosts.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

1.2.  Terminology

   Pref64: an IPv6 prefix used for IPv6 address synthesis [RFC6146];

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

   PvD-aware host A host that supports the association of network
   configuration information into PvDs and the use of these PvDs.  Also
   named PvD-aware node in [RFC7556].

   RA: Router Advertisement, a message used by IPv6 routers to advertise
   their presence together with various link and Internet parameters
   ([RFC4861]);



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2.  Use cases for communicating the NAT64 prefix to hosts

   On networks employing NAT64, it is useful for hosts to know the NAT64
   prefix for several reasons, including the following:

   o  Local DNSSEC validation.  As discussed in [RFC6147] section 2, the
      stub resolver in the host "will try to obtain (real) AAAA RRs, and
      in case they are not available, the DNS64 function will synthesize
      AAAA RRs for internal usage."  This is required in order to use
      DNSSEC on a NAT64 network.

   o  IPv4 address literals on an IPv6-only host.  As described in
      [RFC8305] section 7.1, IPv6-only hosts connecting to IPv4 address
      literals can resolve the IPv4 literal to an IPv6 address.

   o  464XLAT [RFC6877]. 464XLAT is widely deployed and requires that
      the host be aware of the NAT64 prefix.

   o  Trusted DNS server.  AAAA synthesis is required for the host to be
      able to use a DNS server not provided by the network (e.g., a DNS-
      over-TLS server with which the host has an existing trust
      relationship).

   o  Networks with no DNS64 server.  Hosts that support AAAA synthesis
      and that are aware of the NAT64 prefix in use do not need the
      network to perform the DNS64 function at all.

3.  Why include the NAT64 prefix in Router Advertisements

   Fate sharing: NAT64 requires a routing to be configured.  IPv6
   routing configuration requires receiving an IPv6 Router Advertisement
   [RFC4861].  Compared to currently-deployed NAT64 prefix discovery
   methods such as [RFC7050], including the NAT64 prefix in the Router
   Advertisement minimizes the number of packets required to configure a
   host.  This speeds up the process of connecting to a network that
   supports NAT64/DNS64, and simplifies host implementation by removing
   the possibility that the host can have an incomplete layer 3
   configuration (e.g., IPv6 addresses and prefixes, but no NAT64
   prefix).

   Updatability: it is possible to change the NAT64 prefix at any time,
   because when it changes, it is possible to notify hosts by sending a
   new Router Advertisement.

   Deployability: all IPv6 hosts and networks are required to support
   [RFC4861].  Other options such as [RFC7225] require implementing
   other protocols.




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4.  Semantics

   This option only supports a NAT64 prefix length of 96 bits, as this
   is by the most common configuration used by hosts and supporting
   variable prefix length would significantly increase the option size.
   Networks using one of the other prefix lengths supported in
   ([RFC6052]) can use other mechanisms such as [RFC7050] or [RFC7225].
   If different prefix lengths become common, another RA option can be
   created to configure them.

   This option specifies exactly one NAT64 prefix for all IPv4
   destinations.  If the network operator desires to route different
   parts of the IPv4 address space to different NAT64 devices, this can
   be accomplished by routing more specifics of the NAT64 prefix to
   those devices.  For example, if the operator would like to route
   10.0.0.0/8 through NAT64 device A and the rest of the IPv4 space
   through NAT64 device B, and the operator's NAT64 prefix is
   2001:db8:a:b::/96, then the operator can route
   2001:db8:a:b::a00:0/104 to NAT64 A and 2001:db8:a:b::/64 to NAT64 B.

   This option may appear more than once in a Router Advertisement (e.g.
   in case of graceful renumbering the network from one NAT64 prefix to
   another).  Host behaviour with regards to synthesizing IPv6 addresses
   from IPv4 addresses SHOULD follow the recommendations given in
   Section 3 of [RFC7050], limited to the NAT64 prefixes that have non-
   zero lifetime.

   In a network that provides both IPv4 and NAT64, it may be desirable
   for certain IPv4 addresses not to be translated.  An example might be
   private address ranges that are local to the network and should not
   be reached through the NAT64.  This type of configuration cannot be
   conveyed to hosts using this option, or through other NAT64 prefix
   provisioning mechanisms such as [RFC7050] or [RFC7225].  This problem
   does not apply in IPv6-only networks, because in such networks, the
   host does not have an IPv4 address and cannot reach any IPv4
   destinations without the NAT64.

5.  Option format













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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     |           Lifetime            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     +                            Prefix                             +
     |                                                               |
     +                                                               +
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



                   Figure 1: NAT64 Prefix Option Format

   Fields:

   Type     8-bit identifier of the RDNSS option type as assigned by
            IANA: TBD
   Length   8-bit unsigned integer.  The length of the option (including
            the Type and Length fields) is in units of 8 octets. The
            sender MUST set the Length to 2.  A host MUST ignore the
            NAT64 prefix option if the length field value is 1. If the
            Length field value exceeds 2, the host MUST utilize the
            first 16 octets and ignore the rest of the option.
   Lifetime 16-bit unsigned integer.  The maximum time in seconds over
            which this NAT64 prefix MAY be used. The value of Lifetime
            SHOULD by default be set to lesser of  3 x MaxRtrAdvInterval
            or 65535 seconds.  A value of zero means that the prefix
            MUST no longer be used.
   Prefix   The 96-bit NAT64 prefix.

6.  Handling Multiple NAT64 Prefixes

   In some cases a host may receive multiple NAT64 prefixes from
   different sources.  Possible scenarios include (but are not limited
   to):

   o  the host is using multiple mechanisms to discover Pref64 prefixes
      (e.g. by using PCP ([RFC7225]) and/or by resolving IPv4-only fully
      qualified domain name ([RFC7050]) in addition to receiving the
      Pref64 RA option);

   o  The pref64 option presents in a single RA more than once;

   o  the host receives multiple RAs with different Pref64 prefixes on
      one or multiple interfaces.



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   When multiple Pref64 were discovered via RA Pref64 Option (the Option
   presents more than once in a singe RA or multiple RAs were received),
   host behaviour with regards to synthesizing IPv6 addresses from IPv4
   addresses SHOULD follow the recommendations given in Section 3 of
   [RFC7050], limited to the NAT64 prefixes that have non-zero
   lifetime..

   When different Pref64 are discovered by using multiple mechanisms,
   hosts SHOULD select one source of infromation only.  The RECOMMENDED
   order is:

   o  PCP-discovered prefixes ([RFC7225]), if supported;

   o  Pref64 discovered via RA Option;

   o  Pref64 resolving IPv4-only fully qualified domain name ([RFC7050])

   Note that if the network provides Pref64 both via this RA option and
   [RFC7225], hosts that receive the Pref64 via RA option may choose to
   use it imediately before waiting for PCP to complete, and therefore
   some traffic may not reflect any more detailed configuration provided
   by PCP.

7.  Multihoming

   Like most IPv6 configuration information, the Pref64 option is
   specific to the network on which it is received.  For example, a
   Pref64 option received on a particular wireless network may not be
   usable unless the traffic is also sourced on that network.
   Similarly, a host connected to a cellular network that povides NAT64
   generally cannot use that NAT64 for destinations reached through a
   VPN tunnel that terminates outside that network.

   Thus, correct use of this option on a multihomed host generally
   requires the host to be PVD-aware.

   This issue is not specific to the Pref64 RA option and, for example,
   is quite typical for DNS resolving on multihomed hosts (e.g. a host
   might resolve a destination name by using the corporate DNS server
   via the VPN tunnel but then send the traffic via its Internet-facing
   interface).

8.  IANA Considerations

   The IANA is requested to assign a new IPv6 Neighbor Discovery Option
   type for the PREF64 option defined in this document.





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                         +---------------+-------+
                         | Option Name   | Type  |
                         +---------------+-------+
                         | PREF64 option | (TBD) |
                         +---------------+-------+

                                  Table 1

   The IANA registry for these options is:

      https://www.iana.org/assignments/icmpv6-parameters [1]

9.  Security Considerations

   Because Router Advertisements are required in all IPv6 configuration
   scenarios, on IPv6-only networks, Router Advertisements must already
   be secured, e.g., by deploying RA guard [RFC6105].  Providing all
   configuration in Router Advertisements increases security by ensuring
   that no other protocols can be abused by malicious attackers to
   provide hosts with invalid configuration.

   The security measures that must already be in place to ensure that
   Router Advertisements are only received from legitimate sources
   eliminate the problem of NAT64 prefix validation described in section
   3.1 of [RFC7050].

10.  Acknowledgements

   Thanks to the following people (in alphabetical order) for their
   review and feedback: Mikael Abrahamsson, Brian E Carpenter, Nick
   Heatley, Tatuya Jinmei, David Schinazi.

11.  References

11.1.  Normative References

   [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>.

   [RFC6052]  Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
              Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
              DOI 10.17487/RFC6052, October 2010,
              <https://www.rfc-editor.org/info/rfc6052>.






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11.2.  Informative References

   [I-D.ietf-intarea-provisioning-domains]
              Pfister, P., Vyncke, E., Pauly, T., Schinazi, D., and W.
              Shao, "Discovering Provisioning Domain Names and Data",
              draft-ietf-intarea-provisioning-domains-04 (work in
              progress), March 2019.

   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements",
              RFC 4033, DOI 10.17487/RFC4033, March 2005,
              <https://www.rfc-editor.org/info/rfc4033>.

   [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>.

   [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>.

   [RFC6877]  Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT:
              Combination of Stateful and Stateless Translation",
              RFC 6877, DOI 10.17487/RFC6877, April 2013,
              <https://www.rfc-editor.org/info/rfc6877>.

   [RFC7050]  Savolainen, T., Korhonen, J., and D. Wing, "Discovery of
              the IPv6 Prefix Used for IPv6 Address Synthesis",
              RFC 7050, DOI 10.17487/RFC7050, November 2013,
              <https://www.rfc-editor.org/info/rfc7050>.

   [RFC7225]  Boucadair, M., "Discovering NAT64 IPv6 Prefixes Using the
              Port Control Protocol (PCP)", RFC 7225,
              DOI 10.17487/RFC7225, May 2014,
              <https://www.rfc-editor.org/info/rfc7225>.



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

   [RFC7858]  Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
              and P. Hoffman, "Specification for DNS over Transport
              Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
              2016, <https://www.rfc-editor.org/info/rfc7858>.

   [RFC8305]  Schinazi, D. and T. Pauly, "Happy Eyeballs Version 2:
              Better Connectivity Using Concurrency", RFC 8305,
              DOI 10.17487/RFC8305, December 2017,
              <https://www.rfc-editor.org/info/rfc8305>.

11.3.  URIs

   [1] https://www.iana.org/assignments/icmpv6-parameters

Authors' Addresses

   Lorenzo Colitti
   Google
   Roppongi 6-10-1
   Minato, Tokyo  106-6126
   JP

   Email: lorenzo@google.com


   Erik Kline
   Google
   Roppongi 6-10-1
   Minato, Tokyo  106-6126
   JP

   Email: ek@google.com


   Jen Linkova
   Google
   1 Darling Island Rd
   Pyrmont, NSW  2009
   AU

   Email: furry@google.com






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