BGP What?

November 5, 2012 8:28 AM

I need to answer these three questions for Mr. Orsonet. Does anyone know how to find the answers? It's not for a test or anything - nothing nefarious going on.

Q1: After a router reboot you notice you are not receiving any BGP routes from the service provider, what command would you run to verify the BGP neighborship with the service provider and what would you look for?

Q2: What does the command "no synchronization" achieve in a BGP configuration

Q3: At a High Level what 2 commands are required to establish a BGP Neighbor relationship?

posted by orsonet to computers & internet (4 answers total)

That's pretty advanced stuff to be asking about here. Honestly if I have BGP issues I'm on a call to the ISP NOC asap becasue 99% of the time we didn't cause it and we can't fix it.

Regardless, some Cisco/ IOS specific answers below.

A1 - "show ip bgp neighbor" and check the state of the remote end. Google bgp states, but any result other than established means something is going on.

A2 - that command disables synchronization, which is what allows your AS to redistribute IG routes or other AS routes. Sync is disabled by default.

A3 - "2 commands" seems oddly like a test question. You need at minimum 2 pieces of information, remote AS and the remote IP to setup a neighbor, but in cisco land those are entered in the same "command". Maybe they mean add the peer as #1 and then activate the connection as #2? Or enabling BGP on the router as #1 and then add the peer as #2? It's just oddly phrased.

> Does anyone know how to find the answers?

For BGP intro, this cisco doc on basic BGP is pretty good place to start. in general? Google mostly, also on the job training, classes, and enjoying reading networking blogs. Also the book 'Network Warrior' is a must for any networking pro or want-to-be pro.
posted by anti social order at 9:39 AM on November 5, 2012 [1 favorite]

Looks like anti social already gave you most of what you need on this. However, here is a good troubleshooting doc from Cisco on your first Q, and I'd second "show ip bgp neigh" as well as all the other info in the comment above me. Cisco has a score of quality docs online, so I'd imagine some time spent there would pull in all the answers needed, you just have to weed through the massive "Everything you ever wanted to know about BGP" docs. While they are, of course, Cisco/IOS specific, they should translate fairly well to other platforms - there may be some command syntax and terminology changes, but BGP is BGP. Troubleshooting BGP on Juniper routers, just in case - they seem funky (or they did to me at least) if you're coming to them from a Cisco background. I spent a good amount of time relearning firewalls when I went from Cisco Pix to Juniper Netscreen for example - Juniper likes to use terms like vrouter and VIP and MIP.
posted by routergirl at 9:57 AM on November 5, 2012

and then juniper made it all weird again in a different way for their SRX platform (firewall running JunOS)

Important tip for looking at BGP on a cisco. A neighbor state of "Active" does NOT mean that you have an active neighbor relationship. It means that your router is actively trying to talk to the neighbor but hasn't actually got a connection set up with it.
posted by rmd1023 at 10:17 AM on November 5, 2012

Thanks everyone!
posted by orsonet at 10:21 AM on November 5, 2012