v6ops WG                                                        O. Troan
Internet-Draft                                                     Cisco
Obsoletes: 3056, 3068                                      June 24, 2011
(if approved)
Intended status: Informational
Expires: December 26, 2011

  Request to move Connection of IPv6 Domains via IPv4 Clouds (6to4) to
                            Historic status


   Experience with the "Connection of IPv6 Domains via IPv4 Clouds
   (6to4)" IPv6 transitioning mechanism has shown that the mechanism is
   unsuitable for widespread deployment and use in the Internet.  This
   document requests that RFC3056 and the companion document "An Anycast
   Prefix for 6to4 Relay Routers" RFC3068 are made obsolete and moved to
   historic status.

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
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   This Internet-Draft will expire on December 26, 2011.

Copyright Notice

   Copyright (c) 2011 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
   (http://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

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   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.

1.  Introduction

   There would appear to be no evidence of any substantial deployment of
   the variant of 6to4 described in [RFC3056].  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 RFC3056 and RFC3068 be moved to Historic
   status as defined in section 4.2.4 [RFC2026].

   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 6to4 [HUSTON], end users may end
   up disabling IPv6 on hosts, and content providers are reluctant to
   make content available over IPv6.

   [I-D.ietf-v6ops-6to4-advisory] analyses the known operational issues
   and describes a set of suggestions to improve 6to4 reliability, given
   the widespread presence of hosts and customer premises equipment that
   support it.

   The IETF sees no evolutionary future for the mechanism and it is not
   recommended to include this mechanism in new implementations.

   IPv6 Rapid Deployment on IPv4 Infrastructures (6rd) [RFC5969]
   utilizes the same encapsulation and base mechanism as 6to4, and could
   be viewed as a superset of 6to4 (6to4 could be achieved by setting
   the 6rd prefix to 2002::/16).  However, the deployment model is 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

2.  Conventions

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

3.  6to4 operational problems

   6to4 is a mechanism designed to allow isolated IPv6 islands to reach

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   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.  RFC3068 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 as described in section 5.2, RFC3056,
   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.  RFC3056 states that a private address
      [RFC1918] MUST NOT be used. 6to4 will not work in networks that

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      employ other addresses with limited topological span.

4.  Deprecation

   This document formally deprecates the 6to4 transition mechanism and
   the IPv6 6to4 prefix defined in [RFC3056], i.e., 2002::/16.  The
   prefix MUST NOT be reassigned for other use except by a future IETF
   standards action.

   Disabling 6to4 in the IPv6 Internet will take some time.  The initial
   approach is to make 6to4 a service of "last resort" in host
   implementations, ensure that the 6to4 service is disabled by default
   in 6to4 routers, and deploy native IPv6 services.  In order to limit
   the impact of end-users, it is recommended that operators retain
   their existing 6to4 relay routers and follow the recommendations
   found in [I-D.ietf-v6ops-6to4-advisory].  When traffic levels
   diminish, these routers can be decommissioned.

   IPv6 nodes SHOULD treat 6to4 as a service of "last resort" as
   recommended in [I-D.ietf-6man-rfc3484-revise]

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

   Existing implementations and deployments MAY continue to use 6to4.

   The references to 6to4 should be removed as soon as practical from
   the revision of the Special-Use IPv6 Addresses [RFC5156].

   The references to the 6to4 relay anycast addresses (
   should be removed as soon as practical from the revision of the
   Special Use IPv4 addresses [RFC5735].

   Incidental references to 6to4 should be 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, and

5.  IANA Considerations

   IANA is requested to mark the 2002::/16 prefix as "deprecated",
   pointing to this document.  Reassignment of the prefix for any usage
   requires justification via an IETF Standards Action [RFC5226].

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   The delegation of the domain [RFC5158] should be
   left in place.  Redelegation of the domain for any usage requires
   justification via an IETF Standards Action [RFC5226].

   IANA is requested to mark the prefix [RFC3068] as
   "deprecated", pointing to this document.  Redelegation of the domain
   for any usage requires justification via an IETF Standards Action

6.  Security Considerations

   There are no new security considerations pertaining to this document.
   General security issues with tunnels are listed in
   [I-D.ietf-v6ops-tunnel-security-concerns] and more specifically to
   6to4 in [RFC3964] and [I-D.ietf-v6ops-tunnel-loops].

7.  Acknowledgements

   The authors would like to acknowledge Tore Anderson, Dmitry Anipko,
   Jack Bates, Cameron Byrne, Ben Campbell, Gert Doering, Ray Hunter,
   Joel Jaeggli, Kurt Erik Lindqvist, Jason Livingood, Keith Moore, Tom
   Petch, Daniel Roesen and Mark Townsley, James Woodyatt, for their
   contributions and discussions on this topic.

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

   Many thanks to Gunter Van de Velde for documenting the harm caused by
   non-managed tunnels and to stimulate 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.

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   [RFC5156]  Blanchet, M., "Special-Use IPv6 Addresses", RFC 5156,
              April 2008.

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

   [RFC5735]  Cotton, M. and L. Vegoda, "Special Use IPv4 Addresses",
              BCP 153, RFC 5735, January 2010.

8.2.  Informative References

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

              Matsumoto, A., Kato, J., and T. Fujisaki, "Update to RFC
              3484 Default Address Selection for IPv6",
              draft-ietf-6man-rfc3484-revise-03 (work in progress),
              June 2011.

              Carpenter, B., "Advisory Guidelines for 6to4 Deployment",
              draft-ietf-v6ops-6to4-advisory-02 (work in progress),
              June 2011.

              Nakibly, G. and F. Templin, "Routing Loop Attack using
              IPv6 Automatic Tunnels: Problem Statement and Proposed
              Mitigations", draft-ietf-v6ops-tunnel-loops-07 (work in
              progress), May 2011.

              Krishnan, S., Thaler, D., and J. Hoagland, "Security
              Concerns With IP Tunneling",
              draft-ietf-v6ops-tunnel-security-concerns-04 (work in
              progress), October 2010.

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

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

   [RFC5158]  Huston, G., "6to4 Reverse DNS Delegation Specification",
              RFC 5158, March 2008.

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

Author's Address

   Ole Troan

   Email: ot@cisco.com

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