300-415 Question 38
Select 4A network engineer is configuring BFD (Bidirectional Forwarding Detection) on a Cisco SD-WAN environment to ensure fast link failure detection and path selection. The engineer notices that some BFD sessions are not establishing correctly between two SD-WAN edge devices. Which of the following could be the reasons for the issue?
- A
Mismatched BFD timers configured on the SD-WAN edge devices
- B
BFD is disabled globally on one of the SD-WAN edge devices
- C
The transport interfaces between the SD-WAN edge devices are in different VPNs
- D
BFD authentication is misconfigured between the SD-WAN edge devices
- E
The devices are using different system IP addresses
Show answer and explanation
Correct answers: A, B, C, D
Explanation
BFD is used in Cisco SD-WAN to detect link failures rapidly and ensure optimal path selection. However, for BFD sessions to establish successfully, several factors must align: timers must be matched, BFD must be enabled globally, transport interfaces must be in the same VPN, and authentication must be correctly configured if enabled. Mismatched configurations or misalignment in these areas will prevent BFD sessions from forming, leading to potential connectivity issues.
- A. Correct.
Mismatched BFD timers can prevent BFD sessions from being established, as both devices need to agree on the timing parameters.
- B. Correct.
If BFD is disabled globally on one of the devices, no BFD sessions can be initiated or established with any peer.
- C. Correct.
BFD sessions require transport interfaces to be in the same VPN for communication. If they are in different VPNs, the session cannot establish.
- D. Correct.
Misconfigured BFD authentication (e.g., incorrect key or method) can lead to session establishment failure as the devices are unable to authenticate each other.
- E. Incorrect.
System IP addresses being different is not a requirement for BFD to establish. BFD operates at the transport level and is not dependent on system IP address configurations.