Network Working Group R. Chandra Request for Comments: 2842 Redback Networks Inc. Category: Standards Track J. Scudder cisco Systems May 2000 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 (2000). All Rights Reserved.
AbstractCurrently 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.
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.
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. Section 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 in RFC2434. Capability Code values 64 through 127 are to be assigned by IANA, using the "First Come First Served" policy defined in RFC2434. Capability Code values 128 through 255 are for "Private Use" as defined in RFC2434. Heffernan]. [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.
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