v6ops WG                                                        O. Troan
Internet-Draft                                                     Cisco
Obsoletes: 3068 3068, 6732 (if approved)                    B. Carpenter, Ed.
Updates: 6343 (if approved)                            Univ. of Auckland
Intended status: Best Current Practice                 November 13, 2014                 Univ. of Auckland
Expires: May 17, June 13, 2015                                 December 10, 2014

           Deprecating Anycast Prefix for 6to4 Relay Routers


   Experience with the "Connection of IPv6 Domains via IPv4 Clouds
   (6to4)" IPv6 transition mechanism defined in RFC 3056 has shown that
   when used in its anycast mode, the mechanism is unsuitable for
   widespread deployment and use in the
   Internet, especially in its anycast mode. Internet.  This document
   therefore requests that RFC 3068, "An Anycast Prefix for 6to4 Relay
   Routers", be made obsolete and moved to historic status.  It also
   obsoletes RFC 6732 "6to4 Provider Managed Tunnels".  It recommends
   that future products should not support 6to4 anycast and that
   existing deployments should be reviewed.  Thus it updates  This complements the
   guidelines in RFC 6343.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on May 17, June 13, 2015.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified BSD License.

1.  Introduction

   There would appear to be no little evidence of any substantial deployment active use of
   the variant original form of 6to4 described in [RFC3056].  Its  However, its
   extension specified in "An Anycast Prefix for 6to4 Relay Routers"
   [RFC3068] has been shown to have severe practical problems when used
   in the Internet.  This document requests that RFC 3068 and RFC 6732
   be moved to Historic status as defined in section 4.2.4 of [RFC2026].
   It also updates complements the deployment guidelines in [RFC6343].

   6to4 was designed to help transition the Internet from IPv4 to IPv6.
   It has been a good mechanism for experimenting with IPv6, but because
   of the high failure rates seen with anycast 6to4 [HUSTON], end users
   may end up disabling IPv6 on hosts as a result, and some content
   providers have been reluctant to make content available over IPv6.

   [RFC6343] analyses the known operational issues in detail and
   describes a set of suggestions to improve 6to4 reliability, given the
   widespread presence of hosts and customer premises equipment that
   support it.  However, experience shows that operational failures have
   continued despite this advice being available.  Fortunately the
   advice to disable 6to4 by default has been widely adopted in recent
   operating systems, and the failure modes have been largely hidden
   from users by many browsers adopting the "happy eyeballs" "Happy Eyeballs" approach
   [RFC6555].  Nevertheless, a substantial amount of 6to4 traffic is
   still observed and the operational problems caused by 6to4 still

   Although facts are hard to obtain, the remaining successful users of
   anycast 6to4 are likely to be on hosts using the obsolete policy
   table [RFC3484] (which prefers 6to4 above IPv4), without Happy
   Eyeballs, with a route to an operational anycast relay, and accessing
   sites that have a route to an operational return relay.

   IPv6 Rapid Deployment on IPv4 Infrastructures (6rd) [RFC5969]
   explicitly builds on the same encapsulation and base mechanism as 6to4, 6to4 mechanism, and could be viewed as a
   superset of 6to4 (6to4 could be achieved by setting
   the 6rd 6to4, using a service provider prefix to 2002::/16). instead of
   2002::/16.  However, the deployment model is based on service povider
   support, such that 6rd can avoid the problems described here.  In
   this sense, 6rd can be viewed as superseding 6to4 as described in
   section 4.2.4 of
   [RFC2026] [RFC2026].

   Given that native IPv6 support and various reliable transition
   such as 6rd are now becoming common, the IETF sees no evolutionary
   future for the 6to4 mechanism.

2.  Conventions

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

   The word "deprecate" and its derivatives are used only in their
   generic sense of "criticize or express disapproval" and do not have
   any specific normative meaning.  A deprecated function might exist in
   the Internet for many years to allow backwards compatibility.

3.  6to4 operational problems

   6to4 is a mechanism designed to allow isolated IPv6 islands to reach
   each other using IPv6 over IPv4 automatic tunneling.  To reach the
   native IPv6 Internet the mechanism uses relay routers both in the
   forward and reverse direction.  The mechanism is supported in many
   IPv6 implementations.  With the increased deployment of IPv6, the
   mechanism has been shown to have a number of fundamental

   6to4 depends on relays both in the forward and reverse direction to
   enable connectivity with the native IPv6 Internet.  A 6to4 node will
   send IPv4 encapsulated IPv6 traffic to a 6to4 relay, that is
   connected both to the 6to4 cloud and to native IPv6.  In the reverse
   direction a 2002::/16 route is injected into the native IPv6 routing
   domain to attract traffic from native IPv6 nodes to a 6to4 relay
   router.  It is expected that traffic will use different relays in the
   forward and reverse direction.  RFC 3068 adds an extension that
   allows the use of a well known IPv4 anycast address to reach the
   nearest 6to4 relay in the forward direction.

   One model of 6to4 deployment, described in section 5.2 of RFC 3056,
   suggests that a 6to4 router should have a set of managed connections
   (via BGP connections) to a set of 6to4 relay routers.  While this
   makes the forward path more controlled, it does not guarantee a
   functional reverse path.  In any case this model has the same
   operational burden as manually configured tunnels and has seen no
   deployment in the public Internet.

   List of some of the known issues with 6to4:

   o  Use of relays. 6to4 depends on an unknown third party to operate
      the relays between the 6to4 cloud and the native IPv6 Internet.
   o  The placement of the relay can lead to increased latency, and in
      the case the relay is overloaded, packet loss.
   o  There is generally no customer relationship between the end-user
      and the relay operator, or even a way for the end-user to know who
      the relay operator is, so no support is possible.
   o  A 6to4 relay for the reverse path and an anycast 6to4 relay used
      for the forward path, are openly accessible, limited only by the
      scope of routing. 6to4 relays can be used to anonymize traffic and
      inject attacks into IPv6 that are very difficult to trace.
   o  6to4 may silently discard traffic in the case where protocol (41)
      is blocked in intermediate firewalls.  Even if a firewall sent an
      ICMP message unreachable back, an IPv4 ICMP message rarely
      contains enough of the original IPv6 packet so that it can be
      relayed back to the IPv6 sender.  That makes this problem hard to
      detect and react upon by the sender of the packet.
   o  As 6to4 tunnels across the Internet, the IPv4 addresses used must
      be globally reachable.  RFC 3056 states that a private address
      [RFC1918] MUST NOT be used. 6to4 will not work in networks that
      employ other addresses with limited topological span.  In
      particular it will predictably fail in the case of double network
      address translation (NAT444).

   For further analysis, see [RFC6343].

   Peer-to-peer usage of the 6to4 mechanism, not depending on the
   anycast mechanism, might exist in the Internet, largely unknown to
   operators.  This is harmless to third parties and the current
   document is not intended to prevent such traffic continuing.

4.  Deprecation

   This document formally deprecates the anycast 6to4 transition
   mechanism defined in [RFC3068] and the associated anycast IPv4
   address  It is NOT RECOMMENDED to include this mechanism
   in new implementations.  It is no longer considered to be a useful
   service of last resort.

   The prefix MUST NOT be reassigned for other use except
   by a future IETF standards action.

   The basic unicast 6to4 mechanism defined in [RFC3056] and the
   associated 6to4 IPv6 prefix 2002::/16 are not deprecated.  The
   default address selection rules specified in [RFC6724] are not
   modified.  However, if included in implementations, unicast 6to4 MUST
   be disabled by default.

   Implementations capable of acting as 6to4 routers MUST NOT enable
   6to4 without explicit user configuration.  In particular, enabling
   IPv6 forwarding on a device MUST NOT automatically enable 6to4.

   Current operators of an anycast 6to4 relay with the IPv4 address SHOULD review the information in [RFC6343] and the
   present document, and then consider carefully when whether the anycast
   relay can be discontinued as traffic diminishes.  Internet service
   providers that do not operate an anycast relay but do provide their
   customers with a route to SHOULD filter out routes verify that it does in
   fact lead to  However, networks an operational anycast relay, as discussed in
   Section 4.2.1 of [RFC6343].  Furthermore, Internet service providers
   and other network providers MUST NOT originate a route to, unless they actively operate and monitor an anycast 6to4
   relay service as detailed in Section 4.2.1 of [RFC6343].

   Networks SHOULD NOT filter out packets whose source address is, because this is normal 6to4 traffic from a 6to4 return
   relay somewhere in the Internet.

   Operators of a 6to4 return relay announcing responding to the IPv6 prefix
   2002::/16 SHOULD review the information in [RFC6343] and the present
   document, and then consider carefully when whether the return relay can be
   discontinued as traffic diminishes.  To avoid confusion, note that
   nothing in the design of 6to4 assumes or requires that return packets
   are handled by the same relay as outbound packets.  As discussed in
   Section 4.5 of RFC 6343, content providers might choose to continue
   operating such a return relay for the benefit of their own residual 6to4
   clients.  Internet service providers SHOULD announce the IPv6 prefix
   2002::/16 to their own customers if and only if it leads to a
   correctly operating return relay as described in RFC 6343.  IPv6-only
   service providers providers, including those operating a NAT64 service
   [RFC6146], are advised that their own customers need a route to such
   a relay to be available in case a residual 6to4 user served by a different service
   provider attempts to communicate with them.

   The guidelines in Section 4 of [RFC6343] remain valid for those who
   choose to continue operating Anycast 6to4 despite its deprecation.
   However, 6to4 Provider Managed Tunnels [RFC6732] will no longer be

   Incidental references to 6to4 should be reviewed and possibly removed
   from other IETF documents if and when they are updated.  These
   documents include RFC3162, RFC3178, RFC3790, RFC4191, RFC4213,
   RFC4389, RFC4779, RFC4852, RFC4891, RFC4903, RFC5157, RFC5245,
   RFC5375, RFC5971, RFC6071 and RFC6890.

5.  IANA Considerations

   The document creating the IANA IPv4 Special-Purpose Address Registry
   [RFC6890] included the 6to4 relay anycast prefix ( as
   Table 10.  Instead, IANA is requested to mark the
   prefix originally defined by [RFC3068] as "Deprecated (6to4 Relay
   Anycast)", pointing to the present document.  Redelegation of this
   prefix for any usage requires justification via an IETF Standards
   Action [RFC5226].

6.  Security Considerations

   There are no new security considerations pertaining to this document.
   General security issues with tunnels are listed in [RFC6169] and more
   specifically to 6to4 in [RFC3964] and [RFC6324].

7.  Acknowledgements

   The authors would like to acknowledge Tore Anderson, Mark Andrews,
   Dmitry Anipko, Jack Bates, Cameron Byrne, Ben Campbell, Lorenzo
   Colitti, Gert Doering, David Farmer, Nick Hilliard, Philip Homburg,
   Ray Hunter, Joel Jaeggli, Victor Kuarsingh, Kurt Erik Lindqvist,
   Jason Livingood, Keith Moore, Tom Petch, Daniel Roesen, Mark Townsley
   and James Woodyatt for their contributions and discussions on this

   Special thanks go to Fred Baker, Geoff Huston, and Wes George for
   their significant contributions.

   Many thanks to Gunter Van de Velde for documenting the harm caused by
   non-managed tunnels and stimulating the creation of this document.

8.  References

8.1.  Normative References

   [RFC2026]  Bradner, S., "The Internet Standards Process -- Revision
              3", BCP 9, RFC 2026, October 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3056]  Carpenter, B. and K. Moore, "Connection of IPv6 Domains
              via IPv4 Clouds", RFC 3056, February 2001.

   [RFC3068]  Huitema, C., "An Anycast Prefix for 6to4 Relay Routers",
              RFC 3068, June 2001.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

   [RFC6146]  Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
              NAT64: Network Address and Protocol Translation from IPv6
              Clients to IPv4 Servers", RFC 6146, April 2011.

   [RFC6724]  Thaler, D., Draves, R., Matsumoto, A., and T. Chown,
              "Default Address Selection for Internet Protocol Version 6
              (IPv6)", RFC 6724, September 2012.

   [RFC6890]  Cotton, M., Vegoda, L., Bonica, R., and B. Haberman,
              "Special-Purpose IP Address Registries", BCP 153, RFC
              6890, April 2013.

8.2.  Informative References

   [HUSTON]   Huston, , "Flailing IPv6", December 2010,

   [RFC1918]  Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
              E. Lear, "Address Allocation for Private Internets", BCP
              5, RFC 1918, February 1996.

   [RFC3484]  Draves, R., "Default Address Selection for Internet
              Protocol version 6 (IPv6)", RFC 3484, February 2003.

   [RFC3964]  Savola, P. and C. Patel, "Security Considerations for
              6to4", RFC 3964, December 2004.

   [RFC5969]  Townsley, W. and O. Troan, "IPv6 Rapid Deployment on IPv4
              Infrastructures (6rd) -- Protocol Specification", RFC
              5969, August 2010.

   [RFC6169]  Krishnan, S., Thaler, D., and J. Hoagland, "Security
              Concerns with IP Tunneling", RFC 6169, April 2011.

   [RFC6324]  Nakibly, G. and F. Templin, "Routing Loop Attack Using
              IPv6 Automatic Tunnels: Problem Statement and Proposed
              Mitigations", RFC 6324, August 2011.

   [RFC6343]  Carpenter, B., "Advisory Guidelines for 6to4 Deployment",
              RFC 6343, August 2011.

   [RFC6555]  Wing, D. and A. Yourtchenko, "Happy Eyeballs: Success with
              Dual-Stack Hosts", RFC 6555, April 2012.

   [RFC6732]  Kuarsingh, V., Lee, Y., and O. Vautrin, "6to4 Provider
              Managed Tunnels", RFC 6732, September 2012.

Authors' Addresses

   Ole Troan

   Email: ot@cisco.com

   Brian Carpenter (editor)
   Department of Computer Science
   University of Auckland
   PB 92019
   Auckland  1142
   New Zealand

   Email: brian.e.carpenter@gmail.com