Comprehensive and Detailed In-Depth Explanation:
Understanding OSPF Areas and Route Propagation in the Network:
* OSPF Area Types in the Question:
* Area 0 (Backbone Area): Connects all areas and distributes routing information.
* Area 1 (Standard Area): Regular OSPF area that can receive and forward external routes.
* Area 2 (Totally NSSA - Totally Not-So-Stubby Area):
* Does not allow external routes except for a default route injected by the ABR.
* Area 3 (NSSA - Not-So-Stubby Area):
* Allows external routes as Type 7 LSAs but does not accept Type 5 LSAs.
* How External Routes Are Advertised in This Scenario:
* R5 (in Area 3) imports 10.0.5.5/32 as an external route into OSPF.
* Since Area 3 is an NSSA, the external route is advertised as a Type 7 LSA (not Type 5).
* The ABR (R1) converts the Type 7 LSA into a Type 5 LSA and advertises it into Area 0.
* Once in Area 0, this Type 5 LSA can be distributed to other areas except totally stubby or totally NSSA areas.
Route Distribution Analysis:
* R5 (Area 3) # R1 (Area 0, ABR):
* R5 generates a Type 7 LSA for 10.0.5.5/32.
* R1 (ABR) converts this Type 7 LSA into a Type 5 LSA and injects it into Area 0.
* R2 (Area 0) # R3 (Area 0):
* Since Area 0 allows external Type 5 LSAs, R2 and R3 receive 10.0.5.5/32.# R2 and R3 have the route.
* R6 (Area 1) # Connected to Area 0:
* Area 1 is a common area, meaning it can receive external Type 5 LSAs.# R6 has the route.
* R4 (Area 2 - Totally NSSA):
* Totally NSSA areas do NOT accept Type 5 or Type 7 LSAs.
* Instead, they receive only a default route from the ABR (R3).
* Since R4 does not receive external routes explicitly, it does NOT have 10.0.5.5/32.# R4 does NOT have the route.
Final Conclusion:
* # R2, R3, and R6 have the route 10.0.5.5/32.
* # R4 does not have the route because Area 2 is a Totally NSSA and only gets a default route.
Thus, the correct answer is:# R2, R3, and R6 have the route 10.0.5.5/32 in their routing tables.