bgp router-id command

Ran into a problem with my lab where I accidentally gave 2 of my routers the same loopback address (which BGP usually uses as the router-id).

Error was

%BGP-3-NOTIFICATION: received from neighbor 10.0.0.8 (BGP identifier wrong)

So I gave the problem router a unique IP but still got the same errors as you need to reset BGP in some way to get it to advertise a new router-id.

Lots of ways to do this although I did find that the clear ip bgp commands don't help with this (as far as I can tell).

I didn't want to reload or tear down BGP and start over (too easy).

So what I finally decided on was to enter BGP config and use the bgp router-id to explicitly tell BGP to use the new ID. That worked.

I noticed that a possible drawback was that the router-id was now in the start config and so I issued the command no bgp router-id to get rid of the explicit instructions. Worked perfectly and BGP did not even need to restart.

Hope this helps someone although maybe this is beyond the scope of the exam?

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Comments

vinbuck

This is a perfect exercise to illustrate why router ids should be assigned under the routing protocol and not through the default highest ip method. BGP is actually a very robust protocol in terms of being able to modify it without disrupting everything.

This is why I like getting my hands dirty in the lab because you never know where it's going to lead. I was working on labs for SWITCH today and discovered that if you don't shut down your ports while trying to put them into an etherchannel, you can get them into a state known as err-disabled. Had to google that one to figure out how to get everything back to working (you just do a shut/no shut), but I learned a valuable lesson that will be helpful in future troubleshooting.

Good stuff Netwurk...

Netwurk

vinbuck wrote: »

I was working on labs for SWITCH today and discovered that if you don't shut down your ports while trying to put them into an etherchannel, you can get them into a state known as err-disabled.

Even worse, try tearing down an etherchannel without first doing a no shut on the ports. On some switches (like the one I tried it on), it will ignore the spanning tree rules and create a switch crippling endless loop. Cool that I learned these things in my lab as it prevents me from doing things like that at work.