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Confederation has a deficiency. When you change an AS into a confederation, you must
reconfigure the routers, and the topology will be changed.
In large-scale BGP networks, you can use both route reflector and confederation.
MP-BGP
BGP-4 can only advertise IPv4 unicast routing information. Multiprotocol Extensions for BGP-4
(MP-BGP) can advertise routing information for the following address families:
• IPv6 unicast address family.
• IPv4 multicast and IPv6 multicast address families.
PIM uses static and dynamic unicast routes to perform RPF check before creating multicast
routing entries. When the multicast and unicast topologies are different, you can use MP-BGP
to advertise the routes for RPF check. MP-BGP stores the routes in the BGP multicast routing
table. For more information about PIM and RPF check, see IP Multicast Configuration Guide.
• VPNv4 and VPNv6 address families.
For more information about VPNv4 and VPNv6, see MPLS Configuration Guide.
• Labeled IPv4 unicast and IPv6 unicast address families.
MP-BGP advertises IPv4 unicast/IPv6 unicast routes and MPLS labels assigned for the routes.
Labeled IPv4 unicast routes apply to inter-AS Option C for MPLS L3VPN. Labeled IPv6 unicast
routes apply to 6PE and inter-AS Option C for MPLS L3VPN. For more information about
inter-AS Option C, see MPLS Configuration Guide.
• L2VPN address family.
L2VPN information includes label block information and remote peer information. For more
information about L2VPN and VPLS, see MPLS Configuration Guide.
MP-BGP extended attributes
Prefixes and next hops are key routing information. BGP-4 uses update messages to carry the
following information:
• Feasible route prefixes in the Network Layer Reachability Information (NLRI) field.
• Unfeasible route prefixes in the withdrawn routes field.
• Next hops in the NEXT_HOP attribute.
BGP-4 cannot carry routing information for multiple network layer protocols.
To support multiple network layer protocols, MP-BGP defines the following path attributes:
• MP_REACH_NLRI—Carries feasible route prefixes and next hops for multiple network layer
protocols.
• MP_UNREACH_NLRI—Carries unfeasible route prefixes for multiple network layer protocols.
MP-BGP uses these two attributes to advertise feasible and unfeasible routes for different network
layer protocols. BGP speakers not supporting MP-BGP ignore updates containing these attributes
and do not forward them to its peers.
Address family
MP-BGP uses address families and subsequent address families to identify different network layer
protocols for routes contained in the MP_REACH_NLRI and MP_UNREACH_NLRI attributes. For
example, an Address Family Identifier (AFI) of 2 and a Subsequent Address Family Identifier (SAFI)
of 1 identify IPv6 unicast routing information carried in the MP_REACH_NLRI attribute. For address
family values, see RFC 1700.
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