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 1.1.1.1, 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 2.2.2.2, 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.
Hi Romeo,
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:
https://gns3vault.com/blog/bgp-for-beginners
https://gns3vault.com/blog/why-do-we-use-bgp
I’ll revise these sometime in the future.
Rene
Hi @williebrown2463,
If you get this message, it means you are entering a network address instead of an IP address.
1.1.1.0/24 is a network address…
* 1.1.1.0 = network address
* 1.1.1.1 up to 254 are host addresses
* 1.1.1.255 = broadcast address
For R1, try using 1.1.1.1/24
Rene
Hi Laz,
Yes, that’s exactly what i was thinking as an EBGP scenario, as a matter of fact as soon as i sent the question, i realized what i was thinking.
Thanks for clearing it up for me.
Thanks lagapides.
reviewing I understood.
If I need to filter what I redistribute from OSPF to BGP I can do it with filters, for example avoid redistributing private prefixes
regards
Thank you Lazaros!!!