Advanced Configuration and Management Guide

NOTE: Route reflection applies only among IBGP routers within the same AS. You cannot configure a cluster that spans multiple ASs.

Figure 10.3 shows an example of a route reflector configuration. In this example, two routing switches are configured as route reflectors for the same cluster. The route reflectors provide redundancy in case one of the reflectors becomes unavailable. Without redundancy, if a route reflector becomes unavailable, its clients are cut off from BGP4 updates.

AS1 contains a cluster with two route reflectors and two clients. The route reflectors are fully meshed with other BGP4 routers, but the clients are not fully meshed. They rely on the route reflectors to propagate BGP4 route updates.

AS 1

AS 2

 

Cluster 1

Route

Route

Reflector 1

Reflector 2

 

EBGP

IBGP

IBGP

IBGP

Route

Route

Reflector

Reflector

Client 1

Client 2

10.0.1.0

10.0.2.0

Figure 10.3 Example route reflector configuration

Support for RFC 2796

In software release 07.1.10 and higher, route reflection is based on RFC 2796. This updated RFC helps eliminate routing loops that are possible in some implementations of the older specification, RFC 1966.

NOTE: The configuration procedure for route reflection is the same regardless of whether your software release is using RFC 1966 or RFC 2796. However, the operation of the feature is different as explained below.

RFC 2796 provides more details than RFC 1966 regarding the use of the route reflection attributes, ORIGINATOR_ID and CLUSTER_LIST, to help prevent loops.

•ORIGINATOR_ID – Specifies the router ID of the BGP4 router that originated the route. The route reflector inserts this attribute when reflecting a route to an IBGP neighbor. If a BGP4 router receives an advertisement that contains its own router ID as the ORIGINATOR_ID, the router discards the advertisement and does not forward it.

•CLUSTER_LIST – A list of the route reflection clusters through which the advertisement has passed. A cluster contains a route reflector and its clients. When a route reflector reflects a route, the route reflector adds its cluster ID to the front of the CLUSTER_LIST. If a route reflector receives a route that has its own cluster ID, the router discards the advertisement and does not forward it.

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