rfc3065.txt

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   It is reasonable for member ASs of a confederation to share a common
   administration and IGP information for the entire confederation.

   It shall be legal for a BGP speaker to advertise an unchanged
   NEXT_HOP and MULTI_EXIT_DISCRIMINATOR (MED) attribute to peers in a
   neighboring AS within the same confederation.  In addition, the
   restriction against sending the LOCAL_PREFERENCE attribute to peers
   in a neighboring AS within the same confederation is removed.  Path
   selection criteria for information received from members inside a
   confederation MUST follow the same rules used for information
   received from members inside the same autonomous system, as specified
   in [1].

8. Compatability Considerations

   All BGP speakers participating in a confederation must recognize the
   AS_CONFED_SET and AS_CONFED_SEQUENCE segment type extensions to the
   AS_PATH attribute.

   Any BGP speaker not supporting these extensions will generate a
   notification message specifying an "UPDATE Message Error" and a sub-
   code of "Malformed AS_PATH".





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   This compatibility issue implies that all BGP speakers participating
   in a confederation MUST support BGP confederations.  However, BGP
   speakers outside the confederation need not support these extensions.

9. Deployment Considerations

   BGP confederations have been widely deployed throughout the Internet
   for a number of years and are supported by multiple vendors.

   Improper configuration of BGP confederations can cause routing
   information within an AS to be duplicated unnecessarily.  This
   duplication of information will waste system resources, cause
   unnecessary route flaps, and delay convergence.

   Care should be taken to manually filter duplicate advertisements
   caused by reachability information being relayed through multiple
   member autonomous systems based upon the topology and redundancy
   requirements of the confederation.

   Additionally, confederations (as well as route reflectors), by
   excluding different reachability information from consideration at
   different locations in a confederation, have been shown to cause
   permanent oscillation between candidate routes when using the tie
   breaking rules required by BGP [1].  Care must be taken when
   selecting MED values and tie breaking policy to avoid these
   situations.

   One potential way to avoid this is by configuring inter-Member-AS IGP
   metrics higher than intra-Member-AS IGP metrics and/or using other
   tie breaking policies to avoid BGP route selection based on
   incomparable MEDs.

10. Security Considerations

   This extension to BGP does not change the underlying security issues
   inherent in the existing BGP, such as those defined in [6].

11. Acknowledgments

   The general concept of BGP confederations was taken from IDRP's
   Routing Domain Confederations [2].  Some of the introductory text in
   this document was taken from [5].

   The authors would like to acknowledge Bruce Cole of Juniper Networks
   for his implementation feedback and extensive analysis of the
   limitations of the protocol extensions described in this document and
   [5].  We would also like to acknowledge Srihari Ramachandra of Cisco
   Systems, Inc., for his feedback.



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   Finally, we'd like to acknowledge Ravi Chandra and Yakov Rekhter for
   providing constructive and valuable feedback on earlier versions of
   this document.

12. References

   [1] Rekhter, Y. and T. Li, "A Border Gateway Protocol 4 (BGP-4)", RFC
       1771, March 1995.

   [2] Kunzinger, C., Editor, "Inter-Domain Routing Protocol", ISO/IEC
       10747, October 1993.

   [3] Haskin, D., "A BGP/IDRP Route Server alternative to a full mesh
       routing", RFC 1863, October 1995.

   [4] Traina, P. "Autonomous System Confederations for BGP", RFC 1965,
       June 1996.

   [5] Bates, T., Chandra, R. and E. Chen, "BGP Route Reflection An
       Alternative to Full Mesh IBGP", RFC 2796, April 2000.

   [6] Heffernan, A., "Protection of BGP Sessions via the TCP MD5
       Signature Option", RFC 2385, August 1998.




























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13. Authors' Addresses

   Paul Traina
   Juniper Networks, Inc.
   1194 N. Mathilda Ave.
   Sunnyvale, CA 94089 USA

   Phone: [phone]
   EMail: [e-mail]


   Danny McPherson
   Amber Networks, Inc.
   48664 Milmont Drive
   Fremont, CA 94538

   Phone: [phone]
   EMail:  [e-mail]


   John G. Scudder
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose, CA 95134

   Phone: [phone]
   EMail: [e-mail]
























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Appendix A: Comparison with RFC 1965

   The most notable change from [1] is that of reversing the values
   AS_CONFED_SEQUENCE(4) and AS_CONFED_SET(3) to those defined in
   section "AS_CONFED Segment Type Extension".  The reasoning for this
   is that in the initial implementation, which was already widely
   deployed, they were implemented backwards from [4], and as such,
   subsequent implementations implemented them backwards as well.  In
   order to foster interoperability and compliance with deployed
   implementations, they've therefore been changed here as well.

   The "Compatibility Discussion" was removed and incorporated into
   other discussions in the document.  Also, the mention of hierarchical
   confederations is removed.  The use of the term "Routing Domain
   Identifier" was replaced with Member AS Number.

   Finally, the "Deployment Considerations" section was expanded a few
   subtle grammar changes were made and a bit more introductory text was
   added.
































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Full Copyright Statement

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Acknowledgement

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



















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