OSPF, eBGP and iBGP working together

[Anuj Singhi]

Hi Team,

I have setup wherein I have two CE (A & B) routers connected back to back and running ospf. Both these CE are connected to one PE (A & B ) each and running eBGP with them. I am also running ibgp between the CE's along with ospf. Now I am redistributing the ebgp routes in the ospf and ospf routes in the bgp table. The setup is ACTIVE-ACTIVE.

There are couple of downstream switches connected to CE's which are also running ospf with ce and between them.

Now if I disconnect the shutdown the ebgp peering between CE-B and PE-B, my complete site goes down and my route doesn't work through CE-A and PE-A though I can see PE-A is sending the routes to CE-A.

Can anybody help me in finding the root cause for it.

Regards,

Anuj

[paul driver · Accepted solution]

Hello

sounds like trafffic is blackholing when you lose the pe-ce link

You don’t say what routes you receiving from the pe -ce routers

let’s say you are receiving a default from either mpls -  you can then advertise a ospf default via a prefix-list and route-map matching on the bgp defaults with the best path advertising with a better ospf metric type conditionally.

when redistributing into bgp you advertise again via a route map. Allowing everything other then a default

Now  if you lose a pe-ce link your rtr will lose its bgp default thus the ospf default will be removed  then the less preferable default will instead be advertised

Lastly ou also need to check that your ibgp peering is specifying to each other as next- hop-self so it will advertise the ebgp default with its own connected interface