Cisco Systems 3750E manual Configuring Route Dampening, Route-reflector-client, 38-62

Chapter 38 Configuring IP Unicast Routing

Configuring BGP

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.

Beginning in privileged EXEC mode, use these commands to configure a route reflector and clients:

	Command	Purpose
Step 1
	configure terminal	Enter global configuration mode.
Step 2
	router bgp autonomous-system	Enter BGP router configuration mode.
Step 3
	neighbor ip-address peer-group-name	Configure the local router as a BGP route reflector and the
	route-reflector-client	specified neighbor as a client.
Step 4
	bgp cluster-id cluster-id	(Optional) Configure the cluster ID if the cluster has more than
		one route reflector.
Step 5
	no bgp client-to-client reflection	(Optional) Disable client-to-client route reflection. By default,
		the routes from a route reflector client are reflected to other
		clients. However, if the clients are fully meshed, the route
		reflector does not need to reflect routes to clients.
Step 6
	end	Return to privileged EXEC mode.
Step 7
	show ip bgp	Verify the configuration. Display the originator ID and the
		cluster-list attributes.
Step 8
	copy running-config startup-config	(Optional) Save your entries in the configuration file.

Configuring Route Dampening

Route flap dampening is a BGP feature designed to minimize the propagation of flapping routes across an internetwork. A route is considered to be flapping when it is repeatedly available, then unavailable, then available, then unavailable, and so on. When route dampening is enabled, a numeric penalty value is assigned to a route when it flaps. When a route’s accumulated penalties reach a configurable limit, BGP suppresses advertisements of the route, even if the route is running. The reuse limit is a configurable value that is compared with the penalty. If the penalty is less than the reuse limit, a suppressed route that is up is advertised again.

Dampening is not applied to routes that are learned by IBGP. This policy prevents the IBGP peers from having a higher penalty for routes external to the AS.

	Catalyst 3750-E and 3560-E Switch Software Configuration Guide
38-62	OL-9775-02