rfc3068.txt

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   performance.

5.2 Discovery and failover

   The 6to4 routers send packets bound to the v6 Internet by tunneling
   them to the 6to4 anycast address.  These packets will reach the
   closest 6to4 relay router provided by their ISP, or by the closest
   ISP according to inter-domain routing.

   The routes to the relay routers will be propagated according to
   standard IPv4 routing rules.  This ensures automatic discovery.

   If a 6to4 relay router somehow breaks, or loses connectivity to the
   v6 Internet, it will cease to advertise reachability of the 6to4
   anycast prefix.  At that point, the local IGP will automatically
   compute a route towards the "next best" 6to4 relay router.  We expect
   that adequate monitoring tools will be used to guarantee timely
   discovery of connectivity losses.









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RFC 3068        An Anycast Prefix for 6to4 Relay Routers       June 2001


5.3 Access control

   Only those ASes that run 6to4 relay routers and are willing to
   provide access to the v6 network announce a path to the 6to4 anycast
   prefix.  They can use the existing structure of peering and transit
   agreements to control to whom they are willing to provide service,
   and possibly to charge for the service.

5.4 Why do we need a large prefix?

   In theory, a single IP address, a.k.a. a /32 prefix, would be
   sufficient: all IGPs, and even BGP, can carry routes that are
   arbitrarily specific.  In practice, however, such routes are almost
   guaranteed not to work.

   The size of the routing table is of great concern for the managers of
   Internet "default free" networks: they don't want to waste a routing
   entry, which is an important resource, for the sole benefit of a
   small number of Internet nodes.  Many have put in place filters that
   automatically drop the routes that are too specific; most of these
   filters are expressed as a function of the length of the address
   prefix, such as "my network will not accept advertisements for a
   network that is smaller than a /24." The actual limit may vary from
   network to network, and also over time.

   It could indeed be argued that using a large network is a waste of
   the precious addressing resource.  However, this is a waste for the
   good cause of actually moving to IPv6, i.e., providing a real relief
   to the address exhaustion problem.

5.5 Do we need a specific AS number?

   A first version of this memo suggested the use of a specific AS
   number to designate a virtual AS containing all the 6to4 relay
   routers.  The rationale was to facilitate the registration of the
   access point in databases such as the RADB routing registry [RADB].
   Further analysis has shown that this was not required for practical
   operation.

5.6 Will this slow down the move to IPv6 ?

   Some have expressed a concern that, while the assignment of an
   anycast address to 6to4 access routers would make life a bit easier,
   it would also tend to leave things in a transition state in
   perpetuity.  In fact, we believe that the opposite is true.






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RFC 3068        An Anycast Prefix for 6to4 Relay Routers       June 2001


   A condition for easy migration out of the "tunnelling" state is that
   it be easy to have connectivity to the "real" IPv6 network; this
   means that people trust that opting for a real IPv6 address will not
   somehow result in lower performances.  So the anycast proposal
   actually ensures that we don't stay in a perpetual transition.

6 Future Work

   Using a default route to reach the IPv6 Internet has a potential
   drawback: the chosen relay may not be on the most direct path to the
   target v6 address.  In fact, one might argue that, in the early phase
   of deployment, a relay close to the 6to4 site would probably not be
   the site's ISP or the native destination's ISP...it would probably be
   some third party ISP's relay which would be used for transit and may
   have lousy connectivity.  Using the relay closest to the native
   destination would more closely match the v4 route, and quite possibly
   provide a higher degree of reliability.  A potential way to deal with
   this issue is to use a "redirection" procedure, by which the 6to4
   router learns the most appropriate route for a specific destination.
   This is left for further study.

   The practical operation of the 6to4 relay routers requires the
   development of monitoring and testing tools, and the elaboration of
   gradual management practices.  While this document provides general
   guidelines for the design of tools and practice, we expect that the
   actual deployment will be guided by operational experience.

7 Security Considerations

   The generic security risks of 6to4 tunneling and the appropriate
   protections are discussed in [RFC3056].  The anycast technique
   introduces an additional risk, that a rogue router or a rogue AS
   would introduce a bogus route to the 6to4 anycast prefix, and thus
   divert the traffic.  IPv4 network managers have to guarantee the
   integrity of their routing to the 6to4 anycast prefix in much the
   same way that they guarantee the integrity of the generic v4 routing.

8 IANA Considerations

   The purpose of this memo is to document the allocation by IANA of an
   IPv4 prefix dedicated to the 6to4 gateways to the native v6 Internet;
   there is no need for any recurring assignment.

9. Intellectual Property

   The following notice is copied from RFC 2026 [Bradner, 1996], Section
   10.4, and describes the position of the IETF concerning intellectual
   property claims made against this document.



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RFC 3068        An Anycast Prefix for 6to4 Relay Routers       June 2001


   The IETF takes no position regarding the validity or scope of any
   intellectual property or other rights that might be claimed to
   pertain to the implementation or use other technology described in
   this document or the extent to which any license under such rights
   might or might not be available; neither does it represent that it
   has made any effort to identify any such rights.  Information on the
   IETF's procedures with respect to rights in standards-track and
   standards-related documentation can be found in BCP-11.  Copies of
   claims of rights made available for publication and any assurances of
   licenses to be made available, or the result of an attempt made to
   obtain a general license or permission for the use of such
   proprietary rights by implementers or users of this specification can
   be obtained from the IETF Secretariat.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights which may cover technology that may be required to practice
   this standard.  Please address the information to the IETF Executive
   Director.

10 Acknowledgements

   The discussion presented here was triggered by a note that Brad
   Huntting sent to the NGTRANS and IPNG working groups.  The note
   revived previous informal discussions, for which we have to
   acknowledge the members of the NGTRANS and IPNG working groups, in
   particular Scott Bradner, Randy Bush, Brian Carpenter, Steve Deering,
   Bob Fink, Tony Hain, Bill Manning, Keith Moore, Andrew Partan and
   Dave Thaler.

11 References

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

   [RADB]    Introducing the RADB. Merit Networks,
             http://www.radb.net/docs/intro.html.

12 Author's Address

   Christian Huitema
   Microsoft Corporation
   One Microsoft Way
   Redmond, WA 98052-6399

   EMail: [e-mail]





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RFC 3068        An Anycast Prefix for 6to4 Relay Routers       June 2001


13 Full Copyright Statement

   Copyright (C) The Internet Society (2001).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.



















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