An administrator has configured OSPF on a FortiGate with multiple areas. They want to ensure that routes from area 0 are redistributed into area 1, but they notice that routes from area 1 are not appearing in area 0. What is the most likely configuration issue?
Correct. For a router to act as an ABR and exchange routes between areas, it must have interfaces in both area 0 and the other area (area 1). If the router lacks an interface in area 0, it cannot generate Type 3 LSAs, and routes from area 1 will not appear in area 0.
Why this answer
The most likely configuration issue is that the ABR is not properly configured as an ABR – it must have interfaces in both area 0 and area 1. Without an interface in area 0, the router cannot generate Type 3 LSAs (inter-area advertisements) between the areas, so routes from area 1 never appear in area 0. Option B is incorrect because a stub area blocks Type 5 LSAs from entering the stub area, but it does not block Type 3 LSAs from being advertised out of the stub area into the backbone; therefore, stub configuration would not prevent inter-area routes from reaching area 0.
Exam trap
The trap is that candidates often assume that any router connecting area 1 to area 0 is automatically an ABR, but it must have an interface in area 0 to function as an ABR. Without it, the router cannot perform inter-area route advertisement.
How to eliminate wrong answers
Option A is wrong because a firewall policy blocking OSPF packets would prevent OSPF neighbor formation entirely, not selectively block route redistribution from area 1 to area 0 while allowing redistribution from area 0 to area 1. Option C is wrong because redistribution with a route map is used for importing external routes into OSPF (e.g., from other protocols), not for controlling inter-area route advertisement between OSPF areas; inter-area routes are handled by ABR Type 3 LSA generation, not redistribution. Option D is wrong because an ABR must have interfaces in both area 0 and area 1 to function as an ABR; if the ABR were not configured with both areas, it would not be an ABR and inter-area routing would fail entirely, not just in one direction.