Basic BGP implementation

FIGURE 8 . 1 2 Basic BGP implementation
AS100
AS 200
AS 300
R1 R3
R2
10.10.10.0 /30
20.20.20.0 /30
.1 .1
.2 .2
S0
S0
S0
S1
Configuring BGP 261
In order to enable BGP on a device, the following command needs to be entered in global
configuration mode:
router bgp autonomous-system-number
autonomous-system-number - the AS number of the local AS.
Now that you know the relevant command, let’s go ahead and enable BGP on each of the
devices in Figure 8.12:
R1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R1(config)#router bgp 100
R1(config-router)#^Z
R1#
R2#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R2(config)#router bgp 200
R2(config-router)#^Z
R2#
R3#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R3(config)#router bgp 300
R3(config-router)#^Z
R3#
Now that we have enabled BGP on the router, we need to tell the BGP process which
routers we want to form peer relationships with. It’s important to note that BGP requires
you to manually set who your neighbors will be. This is accomplished through the use of
the following command:
neighbor address remote-as autonomous-system-number
address - the IP address of the remote device.
autonomous-system-number - the AS number of the remote device.
Be aware that because every bidirectional peering requires a complementary
neighbor statement on each peer, and because the formula for determining the
number of relationships in a full-mesh environment is n(n�"1)/2, the total number
of neighbor commands is twice that, or n(n�"1). That can be quite a few
neighbor commands.
With this in mind, let’s go ahead and set up our peer relationships for each device:
R1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R1(config)#router bgp 100
R1(config-router)#neighbor 10.10.10.2 remote-as 200
R1(config-router)#^Z
R1#
R2#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R2(config)#router bgp 200
R2(config-router)#neighbor 10.10.10.1 remote-as 100
R2(config-router)#neighbor 20.20.20.1 remote-as 300
R2(config-router)#^Z
R2#
R3#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R3(config)#router bgp 300
R3(config-router)#neighbor 20.20.20.2 remote-as 200
R3(config-router)#^Z
R3#
That’s all there is to a basic BGP configuration. Now that you have the basics down, we’re
going to incorporate configuring iBGP with eBGP.