I found a document on internet that will give some idea on OSPF ABR and Loop Prevention. In that document, they mention This:
- ABR expects summary LSAs from Area 0 only. This means there should be at least one adjacency in FULL state built over Area 0 interface. In case if ABR has such adjacency, it will ignore summary-LSAs received over non-backbone areas. These LSAs will be installed in the database, but not used for SPF calculations.
- ABR will accept and use summary-LSAs learned over non-backbone area if it DOES NOT have a FULL adjacency built over an Area 0 interface. It is safe to do so, since the ABR will not be able to flood the summary back into Area 0 creating routing loops.
Can someone give topology that contradicts to point 1? According to my knowledge, in all the cases ABR will establish FULL neighbor relationship to some other "Router" (P2P) or "DR" (Broadcast) in Area0. Why would they specifically mention point 1. Point 2 make sense because of Point 1