I'm testing in lab environment this topology before to try with production environment: two OSPF ABR's R1 and R2 between backbone area and area 80 configured as totally stub area. Inside of this area 80 I have a router R3 with direct serial links to R1 and R2.
Well, R3 learns two default routes with the same metric to reach area 80 external networks. All seems to work fine.
Now let's assume R1 link to area 0 goes down. The problem which is making me crazy is R3 still learns two default routes pointing to R2 and... Â¿Â¿Â¿R1???
Taking a view to R1 routing table (router which lost it's link to backbone area), this router installs a default route pointing to R3, but if R3 maintain a default route to R1..., we have a loop for ip flows load balanced to R1.
I have tested this issue with totally NSSA area and occurs the same thing.
Is this the usual behavior for NSSA/Stub areas with more than one ABR, if one of the ABR losts it's link to backbone area?
On R1, you have both S0/0 and the loopback in area 0. If you take down F0/0, you still have the loopback up in area 0, and so R1 is still an ABR, and so still generates the default route.
You could put the loopback in area 80. I think that would do the trick.