The multiprotocol BGP for the IPv6 multicast address family feature provides multicast BGP extensions for IPv6 and supports
the same features and functionality as IPv4 BGP. IPv6 enhancements to multicast BGP include support for an IPv6 multicast
address family and network layer reachability information (NLRI) and next hop (the next router in the path to the destination)
attributes that use IPv6 addresses.
Multicast BGP is an enhanced BGP that allows the deployment of interdomain IPv6 multicast. Multiprotocol BGP carries routing
information for multiple network layer protocol address families; for example, IPv6 address family and for IPv6 multicast
routes. The IPv6 multicast address family contains routes used for RPF lookup by the IPv6 PIM protocol, and multicast BGP
IPv6 provides for interdomain transport of the same. Users must use multiprotocol BGP for IPv6 multicast when using IPv6 multicast
with BGP because the unicast BGP learned routes will not be used for IPv6 multicast.
Multicast BGP functionality is provided through a separate address family context. A subsequent address family identifier
(SAFI) provides information about the type of the network layer reachability information that is carried in the attribute.
Multiprotocol BGP unicast uses SAFI 1 messages, and multiprotocol BGP multicast uses SAFI 2 messages. SAFI 1 messages indicate
that the routes are usable only for IP unicast, not IP multicast. Because of this functionality, BGP routes in the IPv6 unicast
RIB must be ignored in the IPv6 multicast RPF lookup.
A separate BGP routing table is maintained to configure incongruent policies and topologies (for example, IPv6 unicast and
multicast) by using IPv6 multicast RPF lookup. Multicast RPF lookup is very similar to the IP unicast route lookup.
No MRIB is associated with the IPv6 multicast BGP table. However, IPv6 multicast BGP operates on the unicast IPv6 RIB when
needed. Multicast BGP does not insert or update routes into the IPv6 unicast RIB.