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Cisco ME 3400 EthernetAccess Switch SoftwareConfiguration Guide
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Chapter32 Configuring IP Unicast Routing
Configuring BGP
Configuring BGP Route Reflectors
BGP requires that all of the IBGP speakers be fully meshed. When a router receives a route from an
external neighbor, it must advertise it to all internal neighbors. To prevent a routing information loop,
all IBPG speakers must be connected. The internal neighbors do not send routes learned from inte rnal
neighbors to other internal neighbors.
With route reflectors, all IBGP speakers need not be fully meshed because a no ther meth od is used to
pass learned routes to neighbors. When you configure an internal BGP peer to be a route reflector, it is
responsible for passing IBGP learned routes to a set of IBGP neighbors. The internal peers of the route
reflector are divided into two groups: client peers and nonclient peers (all the other routers in the
autonomous system). A route reflector reflects routes between these two groups. The route reflector and
its client peers form a cluster. The nonclient peers must be fully meshed with each other, but the client
peers need not be fully meshed. The clients in the cluster do not communicate with IBGP speakers
outside their cluster.
When the route reflector receives an advertised route, it takes one of these actions, depending on the
neighbor:
•A route from an external BGP speaker is advertised to all clients and nonclient peers.
•A route from a nonclient peer is advertised to all clients.
•A route from a client is advertised to all clients and nonclient peers. Hence, the clients ne ed not be
fully meshed.
Usually a cluster of clients have a single route reflector, and the cluster is identified by the r oute reflector
router ID. To increase redundancy and to avoid a single point of failure, a cluster might have more than
one route reflector. In this case, all route reflectors in the cluster must be configured with the same 4-byte
cluster ID so that a route reflector can recognize update s from rout e ref lect ors in th e same clust er. All
the route reflectors serving a cluster should be fully meshed and should have identical sets of client and
nonclient peers.
Beginning in privileged EXEC mode, use these commands to configure a route refl ect or a nd clie nts:
Step6 show ip bgp neighbor
show ip bgp network
Verify the configuration.
Step7 copy running-config startup-config (Optional) Save your entries in the configuration file.
Command Purpose
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 router bgp autonomous-system Enter BGP router configuration mode.
Step3 neighbor ip-address | peer-group-name
route-reflector-client Configure the local router as a BGP route reflector and the
specified neighbor as a client.
Step4 bgp cluster-id cluster-id (Optional) Configure the cluster ID if the cluster has more than
one route reflector.
Step5 no bgp client-to-client reflection (Optional) Disable client-to-client route reflection. By default,
the routes from a route reflector client are reflect ed t o ot her
clients. However, if the clients are fully meshed, the route
reflector does not need to reflect routes to clients.