MP-BGP

BGP-4 supports IPv4 unicasts, but does not support other network layer protocols, such as IPv6.

To support more network layer protocols, IETF extended BGP-4 by introducing Multiprotocol Extensions for BGP-4 (MP-BGP) in RFC 4760.

Routers supporting MP-BGP can communicate with routers not supporting MP-BGP.

In BGP-4, the attributes for IPv4 address format are NLRI, NEXT_HOP and AGGREGATOR (AGGREGATOR contains the IP address of the speaker generating the summary route). They are all carried in updates.

To support multiple network layer protocols, BGP-4 puts information about network layer into NLRI and NEXT_HOP. MP-BGP introduces the following path attributes:

• MP_REACH_NLRI—Multiprotocol Reachable NLRI, for advertising feasible routes and next hops

• MP_UNREACH_NLRI—Multiprotocol Unreachable NLRI, for withdrawing unfeasible routes

These path attributes are both optional non-transitive, so BGP speakers not supporting multiprotocol ignore these attributes and do not forward them to its peers.

MP-BGP uses address families to differentiate network layer protocols. For address family values, see RFC 1700, Assigned Numbers. The system supports multiple MP-BGP extensions, including VPN extension (see MCE Configuration Guide), and IPv6 extension (see "Configuring IPv6 BGP."). Different extensions are configured in respective address family view.

	NOTE: This chapter provides no detailed commands related to any specific extension application in MP-BGP address family view.