300-440 Question 41
Select 3A network engineer has configured Bidirectional Forwarding Detection (BFD) on an OSPF-enabled router to detect failures quickly. However, the BFD sessions are not coming up. Upon investigation, it is found that the neighboring router is configured differently. Which of the following must match between the two routers for BFD sessions to be established?
- A
The BFD timer settings, such as desired minimum transmit interval and required minimum receive interval
- B
The authentication method used by BFD, if enabled
- C
The configured BFD version on both routers
- D
The OSPF router IDs on both routers
- E
The interface MTU values on both sides
Show answer and explanation
Correct answers: A, B, C
Explanation
For a BFD session to be established, critical parameters such as timer settings, authentication (if enabled), and BFD version must match between the two routers. These settings ensure proper negotiation and compatibility for fast failure detection. OSPF router IDs and interface MTU values, while important for other functions, do not affect BFD session establishment.
- A. Correct.
BFD timer settings must match between neighbors for successful negotiation and session establishment. Mismatches can cause the session to fail.
- B. Correct.
If BFD authentication is enabled, both routers must use the same authentication method and credentials for the session to be established.
- C. Correct.
BFD versions must match for compatibility between routers. A version mismatch will prevent the session from being established.
- D. Incorrect.
The OSPF router ID does not directly affect BFD session establishment. It is used for OSPF adjacency formation, not BFD.
- E. Incorrect.
The interface MTU value does not impact BFD session establishment. While MTU mismatches can cause issues in other protocols, it is unrelated to BFD negotiation.