Multihomed to different ISPs BGP, OSPF config

[rgoddard]

Have 2 7206VXR gateways each conected to different ISP via BGP. Getting full routes from ISPs to start - plan to filter later. Migrating from a single ISP via static default, as well as internal static routes. Have OSPF running between gateways as well as some uBRs (add'l non-cisco CMTS will only run RIP or OSPF, hence OSPF choice for igp). Following the Cisco docs and the sample config for multihomed to different ISPs, when we kick in the iBGP config router cpu spikes and some WAN routing gets hammered.

First Question: Must I run iBGP between the 2 gateways to utilize both ISPs via BGP?

Second Question: Doesn't there need to be some redistribution command in the configs for OSPF>BGP, and vice-versa?

[Richard Burts]

Ryan

1) Yes you do need to run IBGP between the 2 gateways. If there is more than one router running BGP within an AS there needs to be a mesh between all BGP speaking routers. That mesh can either be direct peering or can be Route Reflectors.

2) It is considered generally best practice not to redistribute between BGP and the IGP (OSPF in your case). Generally the BGP network statements will find the routes in your routing table that you want it to advertise. And generally having OSPF advertise the default route to its neighbors is sufficient without needing to have OSPF learn LOTS of routes from BGP which it would need to advertise.

HTH

Rick

[rgoddard]

thanks Rick for confirming the iBGP, and addressing the redistribute question.

I've got TAC looking into the cpu spike on iBGP - they say the config looks proper, but then not sure how closely they've looked. Until we can get the iBGP issue resolved, got a nice brand new DS3 sitting idle, so any suggestions are appreciated.

[Richard Burts]

Ryan

It is good that you have a case open with the TAC since they bring the most expertise and resources to troubleshooting things like this. But we can work in parallel with them.

I assume that they have had you capture the output of show process cpu while you had IBGP running? What was consuming most of the cycles?

If you want to post the configs we will take a look at them. (It would also help to have some understanding of the topology of the network - what is connected to what on what kind of interface).

HTH

Rick

[rgoddard]

Rick -

thanks again. "BGP Router" was the real cpu hog - 13% avg. I had to back out the iBGP config immediately after the problem arose, to keep customers happy.

Attaching a rather crude visio of network topology.

Working on some sanitized configs.

[vdadlaney]

Hi Ryan,

I believe that BGP Router does cause a temporary spike when it initiates due to the prefix exchanges between the peers. Was this spike consistent? Can you post an output of the show ip bgp summ at regular intervals. Trying to see if the TblVer changes rapidly which I think would give an indication of how often prefixes are being exchanged. Not sure exactly what the normal increment should be. HTH and please do correct me if I am totally of base on this. Thx

Regards,

Vikram