iBGP and eBGP network

FIGURE 8 . 1 3 iBGP and eBGP network
AS100
AS 200
AS 300
R1 R5
10.10.10.0 /30
20.20.20.0 /30
.1 .1
.2
.1 .1
.2
.2
S0
S0
S0
S0
S0
S1
S1
.2
S1
30.30.30.0 /30
40.40.40.0 /30
R2
R3
R4
264 Chapter 8  Border Gateway Protocol
Armed with this information, let’s go ahead and enable BGP on all of the devices and disable
synchronization on the devices that will be running iBGP:
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)#no synchronization
R2(config-router)#^Z
R2#
R3#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R3(config)#router bgp 200
R3(config-router)#no synchronization
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)#no synchronization
R4(config-router)#^Z
R4#
R5#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R5(config)#router bgp 300
R5(config-router)#^Z
R5#
Now that we have BGP enabled, let’s go ahead and assign the neighbors. Don’t forget the
update-source command for the iBGP connections:
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
Configuring BGP 265
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 3.3.3.3 remote-as 200
R2(config-router)#neighbor 4.4.4.4 remote-as 200
R2(config-router)#neighbor 3.3.3.3 update-source Lo0
R2(config-router)#neighbor 4.4.4.4 update-source Lo0
R2(config-router)#^Z
R2#
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 4.4.4.4 remote-as 200
R3(config-router)#neighbor 2.2.2.2 update-source Lo0
R3(config-router)#neighbor 4.4.4.4 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 20.20.20.1 remote-as 300
R4(config-router)#neighbor 3.3.3.3 remote-as 200
R4(config-router)#neighbor 2.2.2.2 remote-as 200
R4(config-router)#neighbor 3.3.3.3 update-source Lo0
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 300
R4(config-router)#neighbor 20.20.20.2 remote-as 200
R5(config-router)#^Z
R5#
266 Chapter 8  Border Gateway Protocol
As you can see, the configuration of iBGP compared to eBGP isn’t different. What determines
whether the connection is iBGP or eBGP is whether the remote BGP speaker is in the same AS or not.