300-440 Question 117
Single answerAn enterprise network is running OSPF as its routing protocol. A network administrator notices that Area 1 cannot directly connect to the OSPF backbone (Area 0) due to a design constraint. To resolve this, a virtual link is configured between Router A in Area 1 and Router B in Area 0 through Area 2. After the configuration, the virtual link is not functioning as expected. What could be the potential issue?
- A
Router A and Router B do not have a direct physical connection.
- B
The transit area (Area 2) is not configured as a standard OSPF area.
- C
Authentication is not enabled on the virtual link.
- D
Router A and Router B are not Area Border Routers (ABRs).
Show answer and explanation
Correct answer: B
Explanation
A virtual link in OSPF is used to connect a non-backbone area (such as Area 1) to the backbone area (Area 0) when a direct connection is not possible. It is established through a transit area, which must be a standard area. If the transit area is configured as a stub or NSSA, the virtual link will fail because such areas do not allow the propagation of inter-area routes, which are necessary for the virtual link to operate. Ensuring the transit area is a standard area is essential for a successful virtual link setup.
- A. Incorrect.
A direct physical connection between Router A and Router B is not required for a virtual link to function. Virtual links are established logically over a transit area.
- B. Correct.
The transit area for a virtual link must be a standard OSPF area (non-stub and non-NSSA). If the transit area is misconfigured as a stub or NSSA, the virtual link will not function.
- C. Incorrect.
While authentication can enhance security, it is not mandatory for the virtual link to function. The absence of authentication would not cause the virtual link to fail.
- D. Incorrect.
Both Router A and Router B need to be ABRs for the virtual link to function since they need to establish a logical connection through the transit area. If they are not ABRs, the virtual link could not be configured in the first place.