Network Working Group					      R. ChandraRequest for Comments: 3392				Redback NetworksObsoletes: 2842 					      J. ScudderCategory: Standards Track				   Cisco Systems							   November 2002		 Capabilities 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 (2002).  All Rights Reserved.Abstract   This document defines a new Optional Parameter, called Capabilities,   that is expected to facilitate the introduction of new capabilities   in the Border Gateway Protocol (BGP) by providing graceful capability   advertisement without requiring that BGP peering be terminated.   This document obsoletes RFC 2842.1. Introduction   Currently 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.2. Specification of Requirements   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this   document are to be interpreted as described in RFC 2119 [RFC2119].Chandra, et. al.	    Standards Track			[Page 1]RFC 3392	 Capabilities Advertisement with BGP-4	   November 20023. Overview of Operations   When a BGP speaker [BGP-4] 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.   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 (see Section   "Extensions to Error Handling" for more details).  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.  If terminated, such peering SHOULD NOT be   re-established automatically.Chandra, et. al.	    Standards Track			[Page 2]RFC 3392	 Capabilities Advertisement with BGP-4	   November 20024. 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.      Capability Value:	 Capability Value is a variable length field that is interpreted	 according to the value of the Capability Code field.   BGP speakers SHOULD NOT include more than one instance of a   capability with the same Capability Code, Capability Length, and   Capability Value.  Note however, that processing of multiple   instances of such capability does not require special handling, as   additional instances do not change the meaning of announced   capability.   BGP speakers MAY include more than one instance of a capability (as   identified by the Capability Code) with non-zero Capability Length   field, but with different Capability Value, and either the same or   different Capability Length.  Processing of these capability   instances is specific to the Capability Code and MUST be described in   the document introducing the new capability.Chandra, et. al.	    Standards Track			[Page 3]RFC 3392	 Capabilities Advertisement with BGP-4	   November 20025. 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 SHOULD list the set of capabilities that cause the speaker to   send the message.  Each such capability is encoded the same way as it   would be encoded in the OPEN message.6. IANA Considerations   This document defines a Capability Optional Parameter along with an   Capability Code field.  IANA maintains 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 in RFC 2434.  Capability Code values 64   through 127 are to be assigned by IANA, using the "First Come First   Served" policy defined in RFC 2434.	Capability Code values 128   through 255 are for "Private Use" as defined in RFC 2434.7. Security Considerations   This extension to BGP does not change the underlying security issues   inherent in the existing BGP [Heffernan].8. Acknowledgements   The authors would like to thank members of the IDR Working Group for   their review and comments.9. Comparison with RFC 2842   In addition to several minor editorial changes, this document also   clarifies how to handle multiple instances of the same capability.10. 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.   [RFC2119]	Bradner, S., "Key words for use in RFCs to Indicate		Requirement Levels", BCP 14, RFC 2119, March 1997.Chandra, et. al.	    Standards Track			[Page 4]RFC 3392	 Capabilities Advertisement with BGP-4	   November 200211. 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, et. al.	    Standards Track			[Page 5]RFC 3392	 Capabilities Advertisement with BGP-4	   November 200212.  Full Copyright Statement   Copyright (C) The Internet Society (2002).  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, et. al.	    Standards Track			[Page 6]