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Network Working Group                                        P. MarquesRequest for Comments: 2545                          cisco Systems, Inc.Category: Standards Track                                     F. Dupont                                                                  Inria                                                             March 1999Use of BGP-4 Multiprotocol Extensions for IPv6 Inter-Domain RoutingStatus 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 (1999).  All Rights Reserved.Abstract   BGP-4 Multiprotocol Extensions [BGP-MP] defines the format of two BGP   attributes (MP_REACH_NLRI and MP_UNREACH_NLRI) that can be used to   announce and withdraw the announcement of reachability information.   This document defines how compliant systems should make use of those   attributes for the purpose of conveying IPv6 routing information.1. Introduction   The BGP-4 protocol [BGP-4] in particular, and path vector routing   protocols in general, are mostly independent of the particular   Address Family for which the protocol is being used.   IPv6 falls under the generic category of protocols for which BGP-4 is   suitable and, unless stated otherwise in this document, the BGP-4   procedures to apply when using BGP-4 to carry IPv6 reachability   information are those defined in [BGP-4] and in subsequent documents   that extend or update the BGP-4 specification.   In terms of routing information, the most significant difference   between IPv6 and IPv4 (for which BGP was originally designed) is the   fact that IPv6 introduces scoped unicast addresses and defines   particular situations when a particular address scope must be used.   This document concerns itself essentially with the necessary rules to   accommodate IPv6 address scope requirements.Marques & Dupont            Standards Track                     [Page 1]

RFC 2545      BGP-4 Multiprotocol Extensions for IPv6 IDR     March 19992. IPv6 Address Scopes   IPv6 defines 3 unicast address scopes [ADDR-ARCH]: global, site-local   and link-local. Site-local addresses are non-link-local address which   are valid within the scope of a "site" and cannot be exported beyond   it. As this document makes no assumption on the characteristics of a   particular routing realm where BGP-4 is used, it makes no distinction   between global and site-local addresses and refers to both as   "global" or "non-link-local". Network administrators must however   respect address scope restrictions and should be aware that the   concepts of a BGP-4 routing domain and "site" are orthogonal notions   and that they may or may not coincide in a given situation.   Companion IPv6 specifications further define that only link-local   address can be used when generating ICMP Redirect Messages [ND] and   as next hop addresses in some routing protocols (eg. RIPng [RIP]).   This restrictions does imply that an IPv6 router must have a link-   local next hop address for all directly connected routes (routes for   which the given router and the next hop router share a common subnet   prefix).   Link-local addresses are not, however, well suited to be used as next   hop attributes in BGP-4 given the rules defined for this attribute in   the protocol specification [BGP-4].   For the above reasons, when BGP-4 is used to convey IPv6 reachability   information it is sometimes necessary to announce a next hop   attribute that consists of a global address and a link-local address.   The following section describes the rules that should be followed   when constructing the Network Address of Next Hop field of an   MP_REACH_NLRI attribute.3. Constructing the Next Hop field   A BGP speaker shall advertise to its peer in the Network Address of   Next Hop field the global IPv6 address of the next hop, potentially   followed by the link-local IPv6 address of the next hop.   The value of the Length of Next Hop Network Address field on a   MP_REACH_NLRI attribute shall be set to 16, when only a global   address is present, or 32 if a link-local address is also included in   the Next Hop field.   The link-local address shall be included in the Next Hop field if and   only if the BGP speaker shares a common subnet with the entity   identified by the global IPv6 address carried in the Network Address   of Next Hop field and the peer the route is being advertised to.Marques & Dupont            Standards Track                     [Page 2]

RFC 2545      BGP-4 Multiprotocol Extensions for IPv6 IDR     March 1999   In all other cases a BGP speaker shall advertise to its peer in the   Network Address field only the global IPv6 address of the next hop   (the value of the Length of Network Address of Next Hop field shall   be set to 16).   As a consequence, a BGP speaker that advertises a route to an   internal peer may modify the Network Address of Next Hop field by   removing the link-local IPv6 address of the next hop.4. Transport   TCP connections, on top of which BGP-4 messages are exchanged, can be   established either over IPv4 or IPv6. While BGP-4 itself is   independent of the particular transport used it derives implicit   configuration information from the address used to establish the   peering session.  This information (the network address of a peer) is   taken in account in the route dissemination procedure. Thus, when   using TCP over IPv4 as a transport for IPv6 reachability information,   additional explicit configuration of the peer's network address is   required.   Note that the information referred above is distinct from the BGP   Identifier used in the BGP-4 tie breaking procedure. The BGP   Identifier is a 32 bit unsigned integer exchanged between two peers   at session establishment time, within an OPEN message. This is a   system wide value determined at startup which must be unique in the   network and should be derived from an IPv4 address regardless of the   network protocol(s) a particular BGP-4 instance is configured to   convey at a given moment.   The use of TCP over IPv6 as transport protocol for IPv6 reachability   information also has the advantage of providing explicit confirmation   of IPv6 network reachability between two peers.5. Security Considerations   The extensions defined in this document allow BGP to propagate   reachability information about IPv6 routes. As such, no new security   issues are raised beyond those that already exist in BGP-4 and its   use with IPv4.6. Acknowledgments   This document derives from the work on BGP-4 Multiprotocol Extensions   by Tony Bates, Ravi Chandra, Dave Katz and Yakov Rekhter.Marques & Dupont            Standards Track                     [Page 3]

RFC 2545      BGP-4 Multiprotocol Extensions for IPv6 IDR     March 19997. References   [ADDR-ARCH] Hinden, R. and S. Deering, "IP Version 6 Addressing               Architecture",RFC 2373, July 1998.   [BGP-4]     Rekhter, Y. and T. Li, "A Border Gateway Protocol 4               (BGP-4)",RFC 1771, March 1995.   [BGP-MP]    Bates, T., Chandra, R., Katz, D. and Y. Rekhter,               "Multiprotocol Extensions for BGP-4",RFC 2283, February               1998.   [IPv6]      Deering, S. and R. Hinden, "Internet Protocol, Version 6               (IPv6) Specification",RFC 2460, December 1998.   [ND]        Narten, T., Nordmark, E. and W. Simpson, "Neighbor               Discovery for IP Version 6 (IPv6)",RFC 2461, December               1998.   [RIP]       Malkin, G. and R. Minnear, "RIPng for IPv6",RFC 2080, January 1997.8. Author Information   Pedro R. Marques   cisco Systems, Inc.   170 W. Tasman Dr.   San Jose, CA 95134   USA   Phone: +1 408 527-5202   Fax:   +1 408 526-4952   EMail: roque@cisco.com   Francis Dupont   GIE DYADE   INRIA Rocquencourt   Domaine de Voluceau   BP 105   78153 Le Chesnay CEDEX   FRANCE   Phone: +33 1 39 63 52 13   Fax:   +33 1 39 63 58 66   EMail: Francis.Dupont@inria.frMarques & Dupont            Standards Track                     [Page 4]

RFC 2545      BGP-4 Multiprotocol Extensions for IPv6 IDR     March 19999.  Full Copyright Statement   Copyright (C) The Internet Society (1999).  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.Marques & Dupont            Standards Track                     [Page 5]