R3303-HP HSR6800 Routers Layer 3 - IP Routing Configuration Guide

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• Confederation
Confederation is another method to manage growing IBGP connections in an AS. It splits an AS
into multiple sub ASs. In each sub AS, IBGP peers are fully meshed. As shown in Figure 67,
intra-confed
eration EBGP connections are established between sub Ass in AS 200.
Figure 67 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 for 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. MP-BGP can transmit routing information for various network layer
protocols, for example, IPv4 multicasts, IPv6 unicasts, and IPv6 multicasts.
Routers supporting MP-BGP can communicate with routers not supporting MP-BGP.
MP-BGP extended attributes
Prefixes and next hops are key routing information for 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prefixes of unfeasible routes in the withdrawn routes field, and next hops in the NEXT_HOP attribute.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NLRI field, withdrawn routes field, and NEXT_HOP attribute cannot be extended to carry information
about 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.