HP 6125G HP 6125G & 6125G/XG Blade Switches Layer 3 - IP Routing Confi - Page 137

Figure 54 BGP route dampening Peer group You can organize BGP peers with the same attributes into a group to simplify their configurations. When a peer joins the peer group, the peer obtains the same configuration as the peer group. If the configuration of the peer group is changed, the configuration of group members is changed. When a peer is added into a peer group, the peer has the same route update policy as the peer group to improve route distribution efficiency. If an option is configured for both a peer and its peer group, the last configuration takes effect. Community A peer group provides each peer with the same policy. A community provides a group of BGP routers in several ASs with the same policy. Community is a path attribute advertised between BGP peers without being limited by AS. A BGP router can modify the COMMUNITY attribute for a route before sending it to other peers. Besides using well-known COMMUNITY attributes, you can define extended community attributes by using a community list to define a routing policy. Route reflector IBGP peers must be fully meshed to maintain connectivity. If n routers exist in an AS, the number of IBGP connections is n (n-1)/2, and large amounts of network and CPU resources are consumed. Using route reflectors can resolve this issue. In an AS, a router acts as a route reflector, and other routers act as clients connecting to the route reflector. The route reflector forwards routing information between clients, so BGP sessions between clients need not be established. A router that is neither a route reflector nor a client is a non-client, which, as shown in Figure 55, must establish BGP sessions to the route reflector and other non-clients. 127