H3C LS-3100-52P-OVS-H3 Operation Manual page 675

Figure 1-12 BGP route dampening
Peer group
You can organize BGP peers with the same attributes into a group to simplify configurations on them.
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 accordingly.
When a peer is added into a peer group, the peer enjoys 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 makes peers in it enjoy the same policy, while a community makes a group of BGP routers
in several ASs enjoy the same policy. Community is a path attribute and 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 should be fully meshed to maintain connectivity. If there are n routers in an AS, the number
of iBGP connections is n (n-1)/2, and therefore large amounts of network and CPU resources will be
consumed.
Using route reflectors can solve 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, and thus BGP sessions between clients need not be established.
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