Network Working Group R. Chandra
Request for Comments: 3392 Redback Networks
Obsoletes: 2842 J. Scudder
Category: Standards Track Cisco Systems
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 (C) The Internet Society (2002). All Rights Reserved.
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.
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
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
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
| Capability Code (1 octet) |
| Capability Length (1 octet) |
| Capability Value (variable) |
The use and meaning of these fields are as follows:
Capability Code is a one octet field that unambiguously
identifies individual capabilities.