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Network Working Group                                        R. ChandraRequest for Comments: 2842                        Redback Networks Inc.Category: Standards Track                                    J. Scudder                                                          cisco Systems                                                               May 2000Capabilities Advertisement with BGP-4Status 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 (2000).  All Rights Reserved.Abstract   Currently BGP-4 [BGP-4] requires that when a BGP speaker receives an   OPEN message with one or more unrecognized Optional Parameters, the   speaker must terminate BGP peering. This complicates introduction of   new capabilities in BGP.   This document defines new Optional Parameter, called Capabilities,   that is expected to facilitate introduction of new capabilities in   BGP by providing graceful capability advertisement without requiring   that BGP peering be terminated.1. Overview of Operations   When a BGP speaker that supports capabilities advertisement sends an   OPEN message to its BGP peer, the message may include an Optional   Parameter, called Capabilities. The parameter lists the capabilities   supported by the speaker.   A BGP speaker determines the capabilities supported by its peer by   examining the list of capabilities present in the Capabilities   Optional Parameter carried by the OPEN message that the speaker   receives from the peer.   A BGP speaker that supports a particular capability may use this   capability with its peer after the speaker determines (as described   above) that the peer supports this capability.Chandra & Scudder           Standards Track                     [Page 1]

RFC 2842         Capabilities Advertisement with BGP-4          May 2000   A BGP speaker determines that its peer doesn't support capabilities   advertisement, if in response to an OPEN message that carries the   Capabilities Optional Parameter, the speaker receives a NOTIFICATION   message with the Error Subcode set to Unsupported Optional Parameter.   In this case the speaker should attempt to re-establish a BGP   connection with the peer without sending to the peer the Capabilities   Optional Parameter.   If a BGP speaker that supports a certain capability determines that   its peer doesn't support this capability, the speaker may send a   NOTIFICATION message to the peer, and terminate peering. The Error   Subcode in the message is set to Unsupported Capability. The message   should contain the capability (capabilities) that causes the speaker   to send the message.  The decision to send the message and terminate   peering is local to the speaker.  Such peering should not be re-   established automatically.2. Capabilities Optional Parameter (Parameter Type 2):   This is an Optional Parameter that is used by a BGP speaker to convey   to its BGP peer the list of capabilities supported by the speaker.   The parameter contains one or more triples <Capability Code,   Capability Length, Capability Value>, where each triple is encoded as   shown below:      +------------------------------+      | Capability Code (1 octet)    |      +------------------------------+      | Capability Length (1 octet)  |      +------------------------------+      | Capability Value (variable)  |      +------------------------------+   The use and meaning of these fields are as follows:      Capability Code:         Capability Code is a one octet field that unambiguously         identifies individual capabilities.      Capability Length:         Capability Length is a one octet field that contains the length         of the Capability Value field in octets.Chandra & Scudder           Standards Track                     [Page 2]

RFC 2842         Capabilities Advertisement with BGP-4          May 2000      Capability Value:         Capability Value is a variable length field that is interpreted         according to the value of the Capability Code field.   A particular capability, as identified by its Capability Code, may   occur more than once within the Optional Parameter.3. Extensions to Error Handling   This document defines new Error Subcode - Unsupported Capability.   The value of this Subcode is 7. The Data field in the NOTIFICATION   message lists the set of capabilities that cause the speaker to send   the message.  Each such capability is encoded the same way as it was   encoded in the received OPEN message.4. IANA ConsiderationsSection 4 defines a Capability Optional Parameter along with an   Capability Code field. IANA is expected to create and maintain the   registry for Capability Code values. Capability Code value 0 is   reserved. Capability Code values 1 through 63 are to be assigned by   IANA using the "IETF Consensus" policy defined inRFC2434. Capability   Code values 64 through 127 are to be assigned by IANA, using the   "First  Come First Served" policy defined inRFC2434. Capability Code   values 128 through 255 are for "Private Use" as defined inRFC2434.5. Security Considerations   This extension to BGP does not change the underlying security issues   inherent in the existing BGP [Heffernan].6. Acknowledgements   The authors would like to thank members of the IDR Working Group for   their review and comments.7. References   [BGP-4]      Rekhter, Y. and T. Li, "A Border Gateway Protocol 4                (BGP-4)",RFC 1771, March 1995.   [Heffernan]  Heffernan, A., "Protection of BGP Sessions via the TCP                MD5 Signature Option",RFC 2385, August 1998.Chandra & Scudder           Standards Track                     [Page 3]

RFC 2842         Capabilities Advertisement with BGP-4          May 20008. Authors' Addresses   Ravi Chandra   Redback Networks Inc.   350, Holger Way   San Jose, CA 95134   EMail: rchandra@redback.com   John G. Scudder   Cisco Systems, Inc.   170 West Tasman Drive   San Jose, CA 95134   EMail: jgs@cisco.comChandra & Scudder           Standards Track                     [Page 4]

RFC 2842         Capabilities Advertisement with BGP-4          May 20009. Full Copyright Statement   Copyright (C) The Internet Society (2000).  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.Chandra & Scudder           Standards Track                     [Page 5]