RFC 2842 (rfc2842) - Page 2 of 5
Capabilities Advertisement with BGP-4
Alternative Format: Original Text Document
RFC 2842 Capabilities Advertisement with BGP-4 May 2000
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.
2. 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 , 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.
Chandra & Scudder Standards Track