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Chapter 9
BGP Scalability and Advanced Features
Peer Groups
When you maintain a large BGP network, there tend to be many small con-
figuration changes that need to be made to a number of BGP routers. To
avoid making an individual change to each and every router, peer groups
were created. This allows you to place those routers that share common pol-
icies into a group. You then make policy changes to the peer group instead
of to each individual router. Policies in your peer group can be overridden,
but only for incoming updates. The outgoing policies must always be iden-
tical for all of the members in your peer group. Peer group policies include
outbound route maps, distribute lists, filter lists, and prefix lists.
All members of the peer group are internal members of an AS and always
share the same ASN. You can assign a peer group name, but the name is local
only to the router it is configured on; it is not passed to any other router.
To configure a peer group, use the neighbor command followed by the
peer group name and then the peer-group syntax, as shown below:
neighbor peer-group-name peer-group
Let's look at an example of configuring a peer group using the command
and assigning the peer group name of group1 to AS 31,400:
RouterA(config)#router bgp 31400
RouterA(config-router)#neighbor group1 peer-group
We now have to identify the neighboring routers in our peer group using
the neighbor command followed by our BGP peer's IP address, the peer-
syntax, and the peer group's name. Let's take a look at the command
and the syntaxes:
neighbor ip-address peer-group peer-group-name
Let's now use the command to add the two neighbors to RouterA that we
have used in most of the demonstrations in this chapter, those being RouterB
using IP address and RouterC using IP address
RouterA(config)#router bgp 31400
RouterA(config-router)#neighbor group1 peer-group
RouterA(config-router)#neighbor peer-group
RouterA(config-router)#neighbor peer-group
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