OSPF Default Route

[EMES]

We recently had a network event where a card in our core switch would not lock OSPF neighbors. I ended up rebooting this card and was able to restore services. However, I am confused why the network didn't alter the default route in the rest of our routers to redirect traffic. I have attached a simple diagram, red routers are ospf and green routers include BGP. My problem was the link between the green routers and when I tried to get traffic in a peer on the north side(north is up, right?!?) destined for a customer attached via BGP on the south peer, it goes from green to the red just north of it, once it got there, it didn't have a route in it's table for that southern peer, it only has the default route.

So...should it recalculate the default route or should I see a route in the routing table on that first hop away from the green so it doesn't use the default route. The default route is viable so I'm not sure that truly needs recalculated. I do have the following commands on the south BGP router:

enable ospf export e-bgp ExportToBGP
enable ospf export i-bgp ExportToBGP

that policy just states that all networks are accepted:
permit;
cost 2;
cost-type ase-type-1;

[Stephane_Grosj1]

Why do you need EAPS? Isn't it all routed?
I'd be interested in seeing the RIB of the BGP routers for the "faulty" prefixes, and the loopback, and have a view of the RIB from the OSPF router. The BGP config as well, if possible.

[EMES]

i don't see the prefixes, that's why it's falling back to the default route.

correct, all based on prepends.

a card on north green router was not passing traffic but did not fault EAPS, however that happens. This issue with traffic caused the customer BGP session to fail, which is part of the problem but not entirely. When I rebooted that card, all bgp sessions came back up...but in the midst of trying to restore services, i had disabled the interface with the X. When the card came online, all was well but I couldn't reach some of the customers networks. It would route to the first red router away and come back. When I enabled that port, things came back as expected...i'm just concerned that a fiber cut between those locations would cause an issue in the future. Also..now, when i do a show iproute a/24, it will show the actual P2P interface to the south router and not the loopback IP.

[EMES]

essentially one AS, we have a customer connected to both green routers with a private AS...when one peer goes down they just route through the other one. So both green routers receive routes for all networks, say A/24, B/24 and C/24 but one router will get 3 prepends for a subnet and the other will get one prepend so it will send A & B north and C south...one fails, they all default to the other peer.

Your statement about directions is correct. the default route on router just north of northern green points back to the green router. when I do a show iproute it says it originates from ospf. yes, the green routers have an I-peer setup, that is where it decides to send the traffic when it starts the routing process but when it hits the first red router, it gets pointed back where it came from. The peers are setup on the loopback interface and the only way to distribute that is ospf. both routers are setup with next-hop-self.

[Stephane_Grosj1]

Hi,

I'm not sure to fully understand the network diagram. Is that diagram your whole AS, or are there different AS in it?

I'm assuming this is a single AS. So, tell me if I got it right: traffic coming from the upper ring, with a destination to a remote customer connected to the lower green BGP router, would reach the upper green router, and from there it goes to the red router just above it (directly connected to it) and stops there. Correct?

That red router has a default route, as you said, but pointing to what router? From what that default originate? Is it a static route created somewhere and redistributed in OSPF, is it originated from your BGP routers? Which one? Both? What about metric?

Do your BGP routers have an iBGP peering? Did you configure that peering on their loopback, which are redistributed in your OSPF? Do you have next-hop-self set on your iBGP?