5. Extensions to Error Handling

5. Extensions to Error Handling

This document defines a new Error Subcode, Unsupported Capability. The value of this Subcode is 7. The Data field in the NOTIFICATION message MUST list the set of capabilities that causes the speaker to send the message. Each such capability is encoded in the same way as it would be encoded in the OPEN message.

As explained in the "Overview of Operations" section, the Unsupported Capability NOTIFICATION is a way for a BGP speaker to complain that its peer does not support a required capability without which the peering cannot proceed. It MUST NOT be used when a BGP speaker receives a capability that it does not understand; such capabilities MUST be ignored.