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When I filter all LSA advertisements from R5 to R2, I loose all routes on R2 except the E2 route from area 51.  This was strange at first since I still had connection to area 5 that should have advertised routes to me.  I also saw OSPF neighbor up on the connection to the frame cloud, but again, no routes in the routing table.  There are many LSA's in the database, but no routes in the route table. 

I built a Virtual link between R2 and R3 and Voila....routes fill the routing table......

With this troubleshooting I assume that the lack of routes before the virtual link has to do with the fact that R2 had "lost" its link to area 0 even though it was adjacent with R5.  My question is:  What exactly is considered "connected" to area 0? Obviously just having a neighbor on the interface is not enough to consider the router "connected" to are 0.  What LSA does R2 need to see to consider itself connecteds to area 0??

Hello,

As I was thinking about this situation like you as well let me try explain what is going on.

When you stop advertings LSA updates from R5 to R2 you do not stop flow of hellos that originally carried those LSAs. That's why R2 and R5 are still neighbors.

When LSA updates stop flowing routes on R2 will remain in routing table untill LSAs (not being updated any more) time out. MaxAge timer is usually 3600s by default but in my case I think it's just 1800s. When that happens you lose connectivity to all routes on R2.

You could have receive any LSA updates on R2 from R3 as any inter-area routing updates MUST pass area 0. But link R2-R3 is in area 5 and link R2-BB2 in area 51. As you noticed virtual-link between R2 and R3 brought area 0 between R2 and R3 and LSA updates arrived.

This outcome is based on my IOS release 12.4(15)T7 on 2600.

Tom