How do you connect two OSPF autonomous systems?

Question

New member. Pls advise if this post does not belong here. Cheers.
You have two entirely separate OSPF systems. You wish to share routing
information between the two systems, but you don't want to join the
systems into one big OSPF system (you still want two area 0's).
Since OSPF does not use an AS number, as does EIGRP, how do you
redistribute routes between the two systems? Is it as simple as using
an ASBR and redistribute routes as you would any other non-OSPF routing
protocol? In that case, wouldn't configuring two interfaces of an ASBR
to join two different areas, of two different OSPF systems just screw
up the protocol and confuse it?
Thanx
Jim

Answer 1

This is simple, but not so simple. :-) On one of the two routers, run two OSPF processes. Then set the processes up so one runs on all the interfaces except the connecting the two routers, and set the other one up so it runs on the interface connecting the two routers. Redistribute between the two processes.
So, if you have this:
10.2.0.0/16--A--10.1.1.0/24--B--10.3.0.0/16
On A:
router ospf 1
network 10.2.0.0 0.0.255.255 area 0
redistribute ospf 1 (insert metric, type, etc)
router ospf 2
network 10.1.1.0 0.0.0.255 area 0
redistribute ospf 1 (insert metric, type, etc)
On B:
router ospf 1
network 0.0.0.0 0.0.0.0 area 0
I would strongly suggest you use route tags or filters (tags are preferrable) to prevent routing loops between the two ospf processes/domains.
Russ