v6ops WG                                                        O. Troan
Internet-Draft                                                     Cisco
Obsoletes: 3056, 3068                                      April 5, 2011
(if approved)
Intended status: Standards Track
Expires: October 7, 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 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.

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   This Internet-Draft will expire on October 7, 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
   to this document.  Code Components extracted from this document must

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   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

   The managed IPv6 transition mechanism "Connection of IPv6 Domains via
   IPv4 Clouds (6to4)" described in [RFC3056] has rarely if ever been
   deployed.  Its extension 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

   [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.

   Declaring the mechanism historic is not expected to have immediate
   product implications.  The IETF sees no evolutionary future for the
   mechanism and it is not recommended to include this mechanism in new

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
   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

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   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 has manually configured tunnels and has seen no
   deployment in the public Internet.

   6to4 issues:

   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 or even a way for the
      end-user to know who the relay operator is, so no support is
   o  In case of the reverse path 6to4 relay and the anycast forward
      6to4 relay, these have to be open for any address.  Only limited
      by the scope of the routing advertisement. 6to4 relays can be used
      to anonymize traffic and inject attacks into IPv6 that are very
      difficult to trace.
   o  6to4 has no specified mechanism to handle the case where the
      protocol (41) is blocked in intermediate firewalls.  It can not be
      expected that path MTU discovery across the Internet works
      reliably; ICMP messages may be blocked and in any case an IPv4
      ICMP message rarely has enough of the original packet in it to be
      useful to proxy back to the IPv6 sender.
   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
      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.

   It is expected that disabling 6to4 in the IPv6 Internet will take

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   some time.  The initial approach is to make the 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
   service.  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.

   1.  IPv6 nodes SHOULD treat 6to4 as a service of "last resort" as
       recommended in [I-D.ietf-6man-rfc3484-revise]
   2.  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.
   3.  If implemented in future products 6to4 SHOULD be disabled by

   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].

   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].

   IANA is requested to mark the domain [RFC5158] 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].

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7.  Acknowledgements

   The authors would like to acknowledge Jack Bates, Cameron Byrne, Gert
   Doering, Joel Jaeggli, Kurt Erik Lindqvist, Jason Livingood, Keith
   Moore, Daniel Roesen and Mark Townsley, 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.

8.  References

8.1.  Normative References

              Matsumoto, A., Kato, J., and T. Fujisaki, "Update to RFC
              3484 Default Address Selection for IPv6",
              draft-ietf-6man-rfc3484-revise-02 (work in progress),
              March 2011.

              Carpenter, B., "Advisory Guidelines for 6to4 Deployment",
              draft-ietf-v6ops-6to4-advisory-00 (work in progress),
              March 2011.

   [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.

   [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.

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8.2.  Informative References

              Nakibly, G. and F. Templin, "Routing Loop Attack using
              IPv6 Automatic Tunnels: Problem Statement and Proposed
              Mitigations", draft-ietf-v6ops-tunnel-loops-06 (work in
              progress), March 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.

Author's Address

   Ole Troan

   Email: ot@cisco.com

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