H3C S5600 Series Operation Manual page 397

Operation Manual – Routing Protocol
H3C S5600 Series Ethernet Switches
Caution:
If a BGP peer and the peer group containing the BGP peer are configured differently,
the last configuration takes effect.
IV. Community
Different form peer group, you can apply the same policy to BGP routers residing in
different ASs through community. Community is a route attribute transmitted among
BGP peers. It is independent of AS.
Before sending a route with the COMMUNITY attribute to its peers, a BGP router can
change the original COMMUNITY attribute of the route.
Besides the well-known COMMUNITY attributes, you can also use the COMMUNITY
attributes list to customize extended COMMUNITY attributes, so as to control the
routing policy with more flexibility.
V. Router reflector
To ensure the connectivity among the IBGP peers in an AS, you need to make the
IBGP peers fully connected. For an AS with the number of the routers in it being n, you
need 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 of
IBGP peers exist in the AS.
You can decrease the use of network resources and CPU time through route
reflection in this case. That is, use a router as a router reflector (RR) and establish
IBGP connections between the RR and other routers known as clients. Routing
information exchanged between the clients is passed/reflected by the RR. This
eliminates 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
5-13
Chapter 5 BGP Configuration
Figure 5-11.