Peer group configuration

FIGURE 9 . 1 1 Peer group configuration
AS 100
AS 200
R3
R4
R5
R2
192.168.100.0 /24 R1 192.168.200.0 /24
Peer Groups 315
In this example, eBGP has already been configured between R1 and R2. What we need to do
is configure iBGP for AS 200. We will use a peer group on R2 for R3, R4, and R5. R2 will perform
as a route reflector for the AS. Lo0 on routers R3, R4, and R5 will be used as the source
interface for the BGP session to R2. R2 will use its Lo0 interface as the source for the BGP sessions
to all iBGP devices. The addresses for each of the device’s Lo0 interfaces are as follows:
R2-2.2.2.2
R3-3.3.3.3
R4-4.4.4.4
R5-5.5.5.5
The Ethernet segment on R1 with the address of 192.168.100.0 /24 should not be advertised
to R3, R4, and R5. All other routes should be known.
We will start by configuring the route map to block the network 192.168.100.0 /24:
R2#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R2(config)#access-list 1 permit 192.168.100.0 0.0.0.255
R2(config)#route-map PEERGROUPFILTER deny 10
R2(config-route-map)#match ip address 1
R2(config-route-map)#route-map PEERGROUPFILTER permit 20
R2(config-route-map)#exit
R2(config)#
Now that we have configured the route map, we need to create the peer group on R2:
R2(config)#router bgp 200
R2(config-router)#neighbor PEERGROUP1 peer-group
R2(config-router)#
After creating the peer group, we need to configure the update policy:
R2(config-router)#neighbor PEERGROUP1 remote-as 200
R2(config-router)#neighbor PEERGROUP1 route-reflector-client
R2(config-router)#neighbor PEERGROUP1 update-source lo0
R2(config-router)#neighbor PEERGROUP1 route-map PEERGROUPFILTER out
Finally, we need to add the respective peers to the peer group:
R2(config-router)#neighbor 3.3.3.3 peer-group PEERGROUP1
R2(config-router)#neighbor 4.4.4.4 peer-group PEERGROUP1
R2(config-router)#neighbor 5.5.5.5 peer-group PEERGROUP1
R2(config-router)#^Z
R2#
316 Chapter 9  Advanced Border Gateway Protocol
That is all that is needed for the configuration on R2. The configuration on the peers isn’t any
different from a normal BGP configuration:
R3#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R3(config)#router bgp 200
R3(config-router)#neighbor 2.2.2.2 remote-as 200
R3(config-router)#neighbor 2.2.2.2 update-source lo0
R3(config-router)#^Z
R3#
R4#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R4(config)#router bgp 200
R4(config-router)#neighbor 2.2.2.2 remote-as 200
R4(config-router)#neighbor 2.2.2.2 update-source lo0
R4(config-router)#^Z
R4#
R5#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R5(config)#router bgp 200
R5(config-router)#neighbor 2.2.2.2 remote-as 200
R5(config-router)#neighbor 2.2.2.2 update-source lo0
R5(config-router)#^Z
R5#
Peer groups can be used to cut down on the amount of configuration needed in large BGP
networks. They can also help to eliminate errors that occur when attempting to configure multiple
update policies that are supposed to contain the same information.