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Re: BGP unsupported capability code

  • From: Danny McPherson
  • Date: Fri Aug 18 03:47:20 2006

On Aug 17, 2006, at 10:57 PM, Joe Maimon wrote:

If A tries to peer with B, and B sends a BGP capability 64 to A, if A does not support that capability what would proper and/or reasonable behavior for A be?

Speaker A MAY send a NOTIFICATION message with Open Message Error/Error Subcode "Unsupported Capability" and a data field listing capability 64 as the trigger for the NOTIFICATION to speaker B (thereby terminating the session). However, RFC 3392 does NOT require that the local BGP speaker terminate the connection, which has particular utility when considering the implications such a hard requirement may otherwise impose on functions such as dynamic BGP capabilities.

(a "published" source for it, if you could possibly do so.)

a) send

unsupported capability code 64 lengh 6
## 2006-08-17 19:17:05 : [bgp/stack]: send NOTIFICATION msg code (Open-Error)
subcode(Open Message Error: Unsupported Capability) to peer w9.x4.y7.z9 via socket 415

b) ignore it

c) admin defined

rfc3392.txt only appears to address the case where if A tries to peer with B, and B sends a BGP capability 64 to A, if A does not support that capability, B MAY terminate the connection with the above notification.

(section 3 paragraph 5)

If the peer doesn't support the capability and this is conveyed from A to B via a NOTIFICATION message (as illustrated in the log message above), then given the scenario you provide B SHOULD NOT include the capability (64) in any subsequent OPEN message sent to A when attempting to reestablish a BGP connection -- IF B so chooses to attempt to automatically reestablish a connection. Note that the above says SHOULD NOT, not MUST NOT.

I'm not quite sure what your point above is, as I think the
document sufficiently outlines the required behavior.

Although BGP is perhaps (?) still of interest to the NANOG
community, I suspect such protocol intricacies are not and
would submit that queries of nature are best directed to
[email protected]