Network Working Group                                         Enke Chen
Internet Draft                                         Redback Networks
Expiration Date: June 2002                            Srihari R. Sangli
                                                       Procket Networks

                      Dynamic Capability for BGP-4


1. Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026 except that the right to
   produce derivative works is not granted.

   Internet-Drafts are working documents of the Internet Engineering
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   material or to cite them other than as ``work in progress.''

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2. Abstract

   This document defines a new BGP capability termed "Dynamic
   Capability", which would allow the dynamic update of capabilities
   over an established BGP session. This capability would facilitate
   non-disruptive capability changes by BGP speakers.

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Internet Draft      draft-ietf-idr-dynamic-cap-01.txt      December 2001

3. Introduction

   Currently BGP capabilities [BGP-CAP] are only advertised in the OPEN
   message during the session initialization. In order to enable a new
   capability or remove an existing capability (such as an Address
   Family support [BGP-MP]), an established session needs to be reset,
   which may disrupt other services running over the session.

   This document defines a new BGP capability termed "Dynamic
   Capability", which would allow the dynamic update of capabilities
   over an established BGP session. This capability would facilitate
   non-disruptive capability changes by BGP speakers.

4. Dynamic Capability

   The Dynamic Capability is a new BGP capability [BGP-CAP].  The
   Capability code for this Capability is specified in the "IANA
   Considerations" section of this document.  The Capability Length
   field of this Capability is set to 0.

   By advertising the Dynamic Capability to a peer in the OPEN, a BGP
   speaker conveys to the peer that the speaker is capable of receiving
   and properly handling the CAPABILITY message (as defined in the next
   Section) from the peer after the BGP session has been established.

5. Capability Message

   The CAPABILITY Message is a new BGP message type with type code 6.
   In addition to the fixed-size BGP header [BGP-4], the CAPABILITY
   message contains one or more of the following tuples:

               | Action (1 octet)             |
               | Capability Code (1 octet)    |
               | Capability Length (1 octet)  |
               | Capability Value (variable)  |

   The value of the Action field is 0 for advertising a capability, and
   1 for removing a capability.

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Internet Draft      draft-ietf-idr-dynamic-cap-01.txt      December 2001

   The triple <Capability Code, Capability Length, Capability Value> is
   the same as defined in [BGP-CAP], and it specifies a capability for
   which the "Action" shall be applied.

6. Operation

   A BGP speaker that is willing to receive the CAPABILITY message from
   its peer should advertise the Dynamic Capability to the peer using
   BGP Capabilities advertisement [BGP-CAP].

   A BGP speaker may send a CAPABILITY message to its peer only if it
   has received the Dynamic Capability from its peer.

   The Dynamic Capability itself can not be revised dynamically via a
   CAPABILITY message. The lifetime of the Dynamic Capability is the
   duration of the BGP session in which the capability is advertised.

   Upon receiving a CAPABILITY message from its peer, the BGP speaker
   shall update the capabilities previously received from that peer
   based on the "Action" in the message, and then function in accordance
   with the revised capabilities for the peer. Any unrecognized
   capabilities in the message should be ignored.

   It is noted that the dynamic capability update may not be feasible
   and should be disallowed for some capabilities.  One example is the
   four-byte AS number capability [BGP-4BYTE-AS] as its dynamic update
   could introduce ambiguity in parsing the UPDATE messages.

7. IANA Considerations

   This document uses a BGP Capability code to indicate that a BGP
   speaker supports the Dynamic Capability.  The Capability code has
   been assigned by IANA per RFC 2842.

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Internet Draft      draft-ietf-idr-dynamic-cap-01.txt      December 2001

8. Intellectual Property Considerations

   Cisco Systems may seek patent or other intellectual property
   protection for some of all of the technologies disclosed in this
   document. If any standards arising from this document are or become
   protected by one or more patents assigned to Cisco Systems, Cisco
   intends to disclose those patents and license them on reasonable and
   non-discriminatory terms.

9. Security Considerations

   This extension to BGP does not change the underlying security issues.

10. Acknowledgments

   The authors would like to thank Yakov Rekhter, Ravi Chandra, Dino
   Farinacci, Pedro Marques and Chandrashekhar Appanna for their review
   and comments.

11. References

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

   [BGP-MP] T. Bates, R. Chandra, D. Katz, and Y. Rekhter,
   "Multiprotocol Extensions for BGP-4", RFC 2858, June 2000.

   [BGP-CAP] R. Chandra, J. Scudder, "Capabilities Advertisement with
   BGP-4", RFC 2842, May 2000.

   [BGP-4BYTE-AS] Q. Vohra, E. Chen, "BGP support for four-octet AS
   number space", Work in Progress, <draft-ietf-idr-as4bytes-04.txt>,
   September 2001.

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12. Author Information

   Enke Chen
   Redback Networks, Inc.
   350 Holger Way
   San Jose, CA 95134

   Srihari R. Sangli
   Procket Networks, Inc.
   1100 Cadillac Court
   Milpitas, CA 95035

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