Combining 2 OSPF Area 0

dppagc

Assume that I have 2 different companies that are running OSPF area 0.
I want to combine them together using bgp.
Is it possible:

1) If they have overlapping ip addresses?
2) They dont have overlapping ip addresses?

OfWolfAndMan

It depends on how you merge them. If it's an in-place kind of thing and they have conflicting spaces i.e. 10.x.x.x, then you could always advertise their subnets inter-campus using NAT (Meaning one campus sees the 10.x.x.x as a 192.168.x.x, which it doesn't have internally). It depends on who needs to be able to reach what. Route maps and/or route filtering may be applicable depending on the situation.

If they don't have overlapping IPs, and you are using BGP through your SP, the complexity is much less likely to be there. Depending on distance, you could always just purchase a VPLS circuit if it's close enough and you could combine the two OSPF area 0s and that would work too. It depends on how many points of ingress you want.

dppagc

Can you provide more information like sample topology or config? Thanks.

Danielh22185

This sounds strangely fishy, like a school project seeking answers for...

Silverymoon

From the CCNP Route studies I think I remember how this can work. If we take two unconnected area 0's and connect them via area 2.

Both area 0's will pass their route's to area 2 but area 2 will not pass routes from one area 0 to the second area 0. Both area 0's will not know if the other exists. You can connect the two area 0's together with a virtual link and they will become a single area 0 logically.

Merging the two backbone area 0s together would be a nightmare if each network is using multiple ospf areas or even having overlapping networks. Would be better to use bgp which would be the easiest way of merging the two networks and avoid merging both area 0's with a virtual link. Remember all the normal routing rules apply. You can't have two different locations for the same address range without using NAT.