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Cisco ME 3800X and 3600X Switch Software Configuration Guide
OL-23400-01
Chapter 29 Configuring IP Unicast Routing
Configuring BGP
To configure a BGP confederation, you must specify a confederation identifier that acts as the
autonomous system number for the group of autonomous systems. Beginning in privileged EXEC mode,
use these commands to configure a BGP confederation:
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 internal
neighbors to other internal neighbors.
With route reflectors, all IBGP speakers need not be fully meshed because another method 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 need not be
fully meshed.
Usually a cluster of clients have a single route reflector, and the cluster is identified by the route 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 updates from route reflectors in the same cluster. All
the route reflectors serving a cluster should be fully meshed and should have identical sets of client and
nonclient peers.
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
router bgp autonomous-system
Enter BGP router configuration mode.
Step 3
bgp confederation identifier autonomous-system Configure a BGP confederation identifier.
Step 4
bgp confederation peers autonomous-system
[autonomous-system ...]
Specify the autonomous systems that belong to the
confederation and that will be treated as special EBGP peers.
Step 5
end
Return to privileged EXEC mode.
Step 6
show ip bgp neighbor
show ip bgp network
Verify the configuration.
Step 7
copy running-config startup-config
(Optional) Save your entries in the configuration file.
