In this lesson I will show you how to configure EBGP (External BGP) and how to advertise networks. I will be using the following topology:
Let’s start with a simple topology. Just two routers and two autonomous systems. Each router has a network on a loopback interface which we are going to advertise in BGP.
R1(config)#router bgp 1 R1(config-router)#neighbor 192.168.12.2 remote-as 2
R2(config)#router bgp 2 R2(config-router)#neighbor 192.168.12.1 remote-as 1
Use the router bgp command with the AS number to start BGP. Neighbors are not configured automatically this is something you’ll have to do yourself with the neighbor x.x.x.x remote-as command. This is how we configure external BGP.
R1# %BGP-5-ADJCHANGE: neighbor 192.168.12.2 Up
R2# %BGP-5-ADJCHANGE: neighbor 192.168.12.1 Up
If everything goes ok you should see a message that we have a new BGP neighbor adjacency.
R1(config)#router bgp 1 R1(config-router)#neighbor 192.168.12.2 password MYPASS
R2(config)#router bgp 2 R2(config-router)#neighbor 192.168.12.1 password MYPASS
If you like you can enable MD5 authentication by using the neighbor password command. Your router will calculate a MD5 digest of every TCP segment that is being sent.
R1#show ip bgp summary BGP router identifier 184.108.40.206, local AS number 1 BGP table version is 1, main routing table version 1 Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd 192.168.12.2 4 2 10 10 1 0 0 00:07:12 0
R2#show ip bgp summary BGP router identifier 220.127.116.11, local AS number 2 BGP table version is 1, main routing table version 1 Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd 192.168.12.1 4 1 11 11 1 0 0 00:08:33 0
Show ip bgp summary is an excellent command to check if you have BGP neighbors. You also see how many prefixes you received from each neighbor.