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 will 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
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 an MD5 digest of every TCP segment sent.
R1#show ip bgp summary BGP router identifier 188.8.131.52, 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 184.108.40.206, 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.
I would like to know how I can be able to see the ebgp prefixes from my OSPF lan segment without using redistribution of BGP to OSPF?
I would send you the configs and topology I have made if you are interested?
Hi Rane ,
I am a big fan of your blog. I find your lessons very helpful . Can you please publish an lesson " how BGP works " Explanation of the process.
There are many things to learn about BGP. If you are completely new to it then you might like some of my blog posts that I wrote a long time ago:
I’ll revise these sometime in the future.
If you need the prefixes that you learned through EBGP on your internal routers then you have two options:
- Redistribute them into your IGP (not a good idea if you have a LOT of prefixes).
- Run IBGP on your internal routers.
You also need to consider if you really need all EBGP prefixes on your internal routers, maybe a default route in OSPF also does the job…
1st of all thank you for all of your precious writings.
I started reading your BGP blog. But im struggling to find an easy way to start with BGP. Because topics are scattered all over the place. Can’t figure out which topics I should read first. Can you please help and show me the correct order that i should follow to become a BGP guru.