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Network Working Group                                         C. HuitemaRequest for Comments: 3068                                     MicrosoftCategory: Standards Track                                      June 2001An Anycast Prefix for 6to4 Relay RoutersStatus of this Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2001).  All Rights Reserved.Abstract   This memo introduces a "6to4 anycast address" in order to simplify   the configuration of 6to4 routers.  It also defines how this address   will be used by 6to4 relay routers, how the corresponding "6to4   anycast prefix" will be advertised in the IGP and in the EGP.  The   memo documents the reservation by IANA (Internet Assigned Numbers   Authority) of the "6to4 relay anycast prefix."1 Introduction   According to [RFC3056], there are two deployment options for a 6to4   routing domain, depending on whether or not the domain is using an   IPv6 exterior routing protocol.  If a routing protocol is used, then   the 6to4 routers acquire routes to all existing IPv6 networks through   the combination of EGP and IGP.  If no IPv6 exterior routing protocol   is used, the 6to4 routers using a given relay router each have a   default IPv6 route pointing to the relay router.  This second case is   typically used by small networks; for these networks, finding and   configuring the default route is in practice a significant hurdle.   In addition, even when the managers of these networks find an   available route, this route often points to a router on the other   side of the Internet, leading to very poor performance.   The operation of 6to4 routers requires either that the routers   participate in IPv6 inter-domain routing, or that the routers be   provisioned with a default route.  This memo proposes a standard   method to define the default route.  It introduces the IANA assigned   "6to4 Relay anycast prefix" from which 6to4 packets will beHuitema                     Standards Track                     [Page 1]

RFC 3068        An Anycast Prefix for 6to4 Relay Routers       June 2001   automatically routed to the nearest available router.  It allows the   managers of the 6to4 relay routers to control the sources authorized   to use their resource.  It makes it easy to set up a large number of   6to4 relay routers, thus enabling scalability.2 Definitions   This memo uses the definitions introduced in [RFC3056], in particular   the definition of a 6to4 router and a 6to4 Relay Router. It adds the   definition of the 6to4 Relay anycast prefix, 6to4 Relay anycast   address, 6to4 IPv6 relay anycast address, and Equivalent IPv4 unicast   address.2.1 6to4 router (or 6to4 border router)   An IPv6 router supporting a 6to4 pseudo-interface.  It is normally   the border router between an IPv6 site and a wide-area IPv4 network.2.2 6to4 Relay Router   A 6to4 router configured to support transit routing between 6to4   addresses and native IPv6 addresses.2.3 6to4 Relay anycast prefix   An IPv4 address prefix used to advertise an IPv4  route to an   available 6to4 Relay Router, as defined in this memo.   The value of this prefix is 192.88.99.0/242.4 6to4 Relay anycast address   An IPv4 address used to reach the nearest 6to4 Relay Router, as   defined in this memo.   The address corresponds to host number 1 in the 6to4 Relay anycast   prefix, 192.88.99.1.2.5 6to4 IPv6 relay anycast address   The IPv6 address derived from the 6to4 Relay anycast address   according to the rules defined in 6to4, using a null prefix and a   null host identifier.   The value of the address is "2002:c058:6301::".Huitema                     Standards Track                     [Page 2]

RFC 3068        An Anycast Prefix for 6to4 Relay Routers       June 20012.6 Equivalent IPv4 unicast address   A regular IPv4 address associated with a specific 6to4 Relay Router.   Packets sent to that address are treated by the 6to4 Relay Router as   if they had been sent to the 6to4 Relay anycast address.3 Model, requirements   Operation of 6to4 routers in domains that don't run an IPv6 EGP   requires that these routers be configured with a default route to the   IPv6 Internet.  This route will be expressed as a 6to4 address. The   packets bound to this route will be encapsulated in IPv4 whose source   will be an IPv4 address associated to the 6to4 router, and whose   destination will be the IPv4 address that is extracted from the   default route.  We want to arrive at a model of operation in which   the configuration is automatic.   It should also be easy to set up a large number of 6to4 relay   routers, in order to cope with the demand.  The discovery of the   nearest relay router should be automatic; if a router fails, the   traffic should be automatically redirected to the nearest available   router.  The managers of the 6to4 relay routers should be able to   control the sources authorized to use their resource.   Anycast routing is known to cause operational issues: since the   sending 6to4 router does not directly identify the specific 6to4   relay router to which it forwards the packets, it is hard to identify   the responsible router in case of failure, in particular when the   failure is transient or intermittent.  Anycast solutions must thus   include adequate monitoring of the routers performing the service, in   order to promptly detect and correct failures, and also adequate   fault isolation procedures, in order to find out the responsible   element when needed, e.g., following a user's complaint.4 Description of the solution4.1 Default route in the 6to4 routers   The 6to4 routers are configured with the default IPv6 route (::/0)   pointing to the 6to4 IPv6 anycast address.4.2 Behavior of 6to4 relay routers   The 6to4 relay routers that follow the specification of this memo   shall advertise the 6to4 anycast prefix, using the IGP of their IPv4   autonomous system, as if it where a connection to an external   network.Huitema                     Standards Track                     [Page 3]

RFC 3068        An Anycast Prefix for 6to4 Relay Routers       June 2001   The 6to4 relay routers that advertise the 6to4 anycast prefix will   receive packets bound to the 6to4 anycast address.  They will relay   these packets to the IPv6 Internet, as specified in [RFC3056].   Each 6to4 relay router that advertise the 6to4 anycast prefix MUST   also provide an equivalent IPv4 unicast address.  Packets sent to   that unicast address will follow the same processing path as packets   sent to the anycast address, i.e., be relayed to the IPv6 Internet.4.3 Interaction with the EGP   If the managers of an IPv4 autonomous domain that includes 6to4 relay   routers want to make these routers available to neighbor ASes, they   will advertise reachability of the 6to4 anycast prefix.  When this   advertisement is done using BGP, the initial AS path must contain the   AS number of the announcing AS.  The AS path should also include an   indication of the actual router providing the service; there is a   suggestion to perform this function by documenting the router's   equivalent IPv4 address in the BGP aggregator attribute of the path;   further work is needed on this point.   The path to the 6to4 anycast prefix may be propagated using standard   EGP procedures.  The whole v6 network will appear to v4 as a single   multi-homed network, with multiple access points scattered over the   whole Internet.4.4 Monitoring of the 6to4 relay routers   Any 6to4 relay router corresponding to this specification must   include a monitoring function, to check that the 6to4 relay function   is operational.  The router must stop injecting the route leading to   the 6to4 anycast prefix immediately if it detects that the relay   function is not operational.   The equivalent IPv4 address may be used to check remotely that a   specific router is operational, e.g., by tunneling a test IPv6 packet   through the router's equivalent unicast IPv4 address.  When a domain   deploys several 6to4 relay routers, it is possible to build a   centralized monitoring function by using the list of equivalent IPv4   addresses of these routers.4.5 Fault isolation   When an error is reported, e.g., by a user, the domain manager should   be able to find the specific 6to4 relay router that is causing the   problem.  The first step of fault isolation is to retrieve the   equivalent unicast IPv4 address of the router used by the user.  If   the router is located within the domain, this information will haveHuitema                     Standards Track                     [Page 4]

RFC 3068        An Anycast Prefix for 6to4 Relay Routers       June 2001   to be retrieved from the IGP tables.  If the service is obtained   through a peering agreement with another domain, the information will   be retrieved from the EGP data, e.g., the BGP path attributes.   The second step is obviously to perform connectivity tests using the   equivalent unicast IPv4 address.5 Discussion of the solution   The initial surfacing of the proposal in the NGTRANS working group   helped us discover a number of issues, such as scaling concerns, the   size of the address prefix, the need for an AS number, and concerns   about risking to stay too long in a transition state.5.1 Does it scale ?   With the proposed scheme, it is easy to first deploy a small number   of relay routers, which will carry the limited 6to4 traffic during   the initial phases of IPv6 deployment.  The routes to these routers   will be propagated according to standard peering agreements.   As the demand for IPv6 increases, we expect that more ISPs will   deploy 6to4 relay routers.  Standard IPv4 routing procedures will   direct the traffic to the nearest relay router, assuring good   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.Huitema                     Standards Track                     [Page 5]

RFC 3068        An Anycast Prefix for 6to4 Relay Routers       June 20015.3 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.Huitema                     Standards Track                     [Page 6]

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 fromRFC 2026 [Bradner, 1996],Section10.4, and describes the position of the IETF concerning intellectual   property claims made against this document.Huitema                     Standards Track                     [Page 7]

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 inBCP-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: huitema@microsoft.comHuitema                     Standards Track                     [Page 8]

RFC 3068        An Anycast Prefix for 6to4 Relay Routers       June 200113 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.Huitema                     Standards Track                     [Page 9]