Network Working Group                                         R. Chandra
Request for Comments: 3392                              Redback Networks
Obsoletes: 2842                                               J. Scudder
Category: Standards Track                                  Cisco Systems
                                                          November 2002


                Capabilities Advertisement with BGP-4

Status 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].









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3. 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.


















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4. 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.




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5. 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.







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11. Authors' Addresses

  Ravi Chandra
  Redback Networks Inc.
  350, Holger Way
  San Jose, CA 95134

  EMail: [email protected]


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

  EMail: [email protected]



































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12.  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.



















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