BGP supports the negotiation of the following capabilities between BGP peers:
- IPv4 unicast address family
- IPv4 multicast address family
- IPv6 unicast address family
- IPv6 multicast address family
- Route-refresh (code = 64 and Cisco-style code = 128)
- 4-byte-AS (code = 65)
BGP brings up peering with the minimal common capability for the both sides. For example, if a local router with both unicast and multicast capabilities peers with a remote router with unicast capability, the local router establishes the connection with unicast-only capability.
When there are no common capabilities, BGP sends an Unsupported Capability error and resets the connection. A manual intervention and configuration change might be required in order to establish a BGP peering session in this particular case.
NoteExtremeXOS version 12.0 and earlier does not negotiate address families. By default, ExtremeXOS version 12.1 advertises MBGP options and is rejected by switches running previous versions, which can delay the establishment of a BGP session. We recommend that you disable the capability advertisement feature of MBGP while peering with switches running previous versions of ExtremeXOS for faster neighbor session establishment.