System information

Configuring BGP
12-15
Configuring a Route Reflector
A BGP speaker cannot advertise a route to an IBGP neighbor if that BGP speaker
originally heard the route from another IBGP speaker. The result of the this rule
requires a full mesh of IBGP sessions within an AS to fully distribute routes via IBGP.
If an AS has many BGP speakers, the number of peer connections can become very
large.
A route reflector alleviates this problem. A route reflector is a BGP speaker that
learns routes from an IBGP neighbor and advertises the routes to other IBGP
neighbors. A route reflector client is a router within the same AS that depends on a
router reflector to readvertise its routes to the entire AS and to learn about routes from
the rest of the AS.
Figure 12-6 shows how a route reflector works. Without Router Los Angeles as a
route reflector, the network requires a full IBGP mesh and that Router New York is a
peer of Router Boston.
Figure 12-6 A BGP Route Reflector
AS 100
AS 200
AS 300
AS 400
LA
2.2.2.2
1.1.1.1
NY
Boston