F3726, F3211, F3174, R5135, R3816-HP Firewalls and UTM Devices Appendix Protocol Reference-6PW100

41
Figure 31 Confederation network diagram
A non-confederation BGP speaker does not need to know sub-ASs in the confederation. It
considers the confederation as one AS, and the confederation ID as the AS number. In the above
figure, AS 200 is the confederation ID.
Confederation has a deficiency. When you change an AS into a confederation, you must
reconfigure your routers, and the topology will be changed.
In large-scale BGP networks, both route reflector and confederation can be used.
MP-BGP
BGP-4 transmits IPv4 unicast routes, but does not transmit routing information of other network layer
protocols, such as IPv6.
To support more network layer protocols, IETF extended BGP-4 by introducing Multiprotocol Border
Gateway Protocol (MP-BGP). MP-BGP can transmit routing information of various network layer protocols,
for example, IPv4 multicasts, IPv6 unicasts, IPv6 multicasts, and VPNv4 routes.
Routers supporting MP-BGP can communicate with routers not supporting MP-BGP.
MP-BGP extended attributes
Prefixes and next hops are key routing information of network layer protocols. In BGP-4, each update
message can carry prefixes of feasible routes in the Network Layer Reachability Information (NLRI) field,
prefixes of unfeasible routes in the withdrawn routes field, and next hops in the NEXT_HOP attribute. The
NLRI field, withdrawn routes field, and NEXT_HOP attribute cannot be extended to carry information of
multiple network layer protocols.
To support multiple network layer protocols, MP-BGP defines the following path attributes:
• MP_REACH_NLRI—Multiprotocol Reachable NLRI, for carrying prefixes of feasible routes and next
hops for multiple network layer protocols. Such routes can then be advertised.
• MP_UNREACH_NLRI—Multiprotocol Unreachable NLRI, for carrying prefixes of unfeasible routes
for multiple network layer protocols. Such routes can then be withdrawn.