Operation Manual – Routing ProtocolH3C S5600 Series Ethernet Switches Chapter 5 BGP Configuration5-13Caution:If a BGP peer and the peer group containing the BGP peer are configured differently,the last configuration takes effect.IV. CommunityDifferent form peer group, you can apply the same policy to BGP routers residing indifferent ASs through community. Community is a route attribute transmitted amongBGP peers. It is independent of AS.Before sending a route with the COMMUNITY attribute to its peers, a BGP router canchange the original COMMUNITY attribute of the route.Besides the well-known COMMUNITY attributes, you can also use the COMMUNITYattributes list to customize extended COMMUNITY attributes, so as to control therouting policy with more flexibility.V. Router reflectorTo ensure the connectivity among the IBGP peers in an AS, you need to make theIBGP peers fully connected. For an AS with the number of the routers in it being n, youneed to establish at least n*(n-1)/2 IBGP connections to make them fully connected.This requires large amount of network resources and CPU time if large amount ofIBGP peers exist in the AS.You can decrease the use of network resources and CPU time through routereflection in this case. That is, use a router as a router reflector (RR) and establishIBGP connections between the RR and other routers known as clients. Routinginformation exchanged between the clients is passed/reflected by the RR. Thiseliminates the need to establish IBGP connections among the clients.Note that a BGP router which is neither the RR nor a client is called a non-client.Non-clients and the RR must be fully connected, as shown in Figure 5-11.
