300-415 Question 39
Select 3A network engineer is configuring BFD (Bidirectional Forwarding Detection) for a Cisco SD-WAN overlay to ensure rapid failure detection between vEdge routers. The engineer notices that the BFD session was not established between two vEdge devices. Which of the following could be the cause of the issue?
- A
The BFD hello interval is mismatched between the two devices.
- B
One of the devices is configured to use a private IP address for the tunnel endpoint.
- C
The BFD multiplier value is set to 1 on both devices.
- D
The TLOC color used for the transport is different between the two devices.
- E
The MTU size on the WAN interface is misconfigured.
Show answer and explanation
Correct answers: A, D, E
Explanation
BFD is a critical component of Cisco SD-WAN to ensure rapid failure detection and convergence. For a BFD session to be established between two devices, certain parameters must match, including the BFD hello interval and TLOC colors. Additionally, misconfigured MTU sizes can prevent packet exchange needed to establish the session. Understanding these requirements is essential for troubleshooting BFD-related issues in SD-WAN deployments.
- A. Correct.
A mismatch in BFD hello intervals between devices can prevent the establishment of a BFD session, as both endpoints must agree on the timing parameters.
- B. Incorrect.
The use of a private IP address for the tunnel endpoint will not inherently prevent BFD sessions as long as NAT traversal is correctly configured and the devices can communicate.
- C. Incorrect.
A BFD multiplier value of 1 is valid, although it may result in very rapid session teardown upon hello packet loss. It would not prevent the session from being established.
- D. Correct.
The TLOC color must match between devices for a BFD session to be established, as it identifies the transport path for the tunnel.
- E. Correct.
An MTU size mismatch can cause packet fragmentation or loss, which may prevent the successful negotiation of BFD sessions.