150-820 · Question #202
You need to configure an OSPF virtual link in an existing fabric. Which two parameter fields must be defined? (Choose two)
The correct answer is A. transit area ID B. neighbor router. See the full explanation below for the reasoning.
Question
You need to configure an OSPF virtual link in an existing fabric. Which two parameter fields must be defined? (Choose two)
Options
- Atransit area ID
- Bneighbor router
- CRBridge ID
- Ddefault router ID
How the community answered
(40 responses)- A80% (32)
- C13% (5)
- D8% (3)
Community Discussion
6
Grace U.Apr 21, 2026The answer is A and B, transit area ID and neighbor router, and once you see why, it sticks. A virtual link is essentially a logical tunnel you build through a transit area to reconnect a partitioned area back to the backbone, so OSPF inherently needs two pieces of information to build that tunnel: which area it is traveling through, and the router ID of the peer at the far end. Without the transit area ID, OSPF has no idea what path the virtual link is following, and without the neighbor router ID, it has no endpoint to form an adjacency with. Options C and D are distractors, RBridge ID belongs to TRILL and FabricPath concepts, and there is no such configuration field as a default router ID in this context. If you missed this one, it just means the virtual link concept needs a little more time to settle, which is completely normal at this stage of prep.
Yusuf A.Apr 23, 2026Worth adding that both endpoints of that virtual link have to be ABRs, which my senior pointed out is what makes the neighbor router ID specifically mean the far-end ABR's Router ID and not just any reachable IP in the transit area.
Wesley A.Apr 14, 2026A and B are your answers, and here is why they stick once you understand what a virtual link actually does. The whole point of a virtual link is to extend the backbone to a disconnected area, and to do that the router has to know which area it is tunneling through (the transit area ID) and which specific router is sitting at the other end of that tunnel (the neighbor router ID). C is there to trip up anyone who has been studying TRILL or FabricPath alongside OSPF, because RBridge ID is a fabric concept that has nothing to do with OSPF virtual link config, and D is just noise since the default router ID is not something you hand-define in this context. First time I sat this exam I second-guessed myself on a question almost identical to this one and circled C thinking the fabric context made it relevant, which cost me. When I came back and took it again I had drilled enough scenarios to recognize that the two required fields map directly to the two endpoints of the logical path, the area in between and the router on the other side, and I locked in A and B without hesitation.
Yusuf A.Apr 10, 2026Totally blanked on this one at first but then remembered when my senior set up a virtual link on a non-backbone area and had to specify both the transit area and the far-end neighbor router address, so I went with A and B and it clicked right away. That hands-on moment saved me because C and D are just distractors that sound official but have nothing to do with what OSPF actually needs to form that logical connection across the transit area.
Bao N.Apr 13, 2026Solid recall, though worth drilling that the transit area itself has to be backbone-adjacent or that virtual link just refuses to come up, which catches people off guard on the sim questions.
Bao N.Apr 30, 2026The neighbor router field trips people up because some vendors call it the remote router ID in their GUI, so if you saw "default router ID" as option D you might second-guess yourself, but default router ID is not a thing you configure for a virtual link. Transit area ID and neighbor router are the two required fields, full stop.