300-510 practice question 7 of 35

Which statement about BFD on Cisco IOS XR Software is true?

Answer options

A: Cisco IOS XR router must use LDP to route back to the Cisco IOS router to establish the peer relationship.

B: Cisco IOS XR Software does not support BFD multihop for IPv4.

C: Cisco IOS XR router must use dynamic routing or a static route back to the Cisco IOS router to establish the peer relationship. Correct answer

D: BFD is not compatible between Cisco IOS XR and Cisco IOS Software.

Correct Answer:

C. Cisco IOS XR router must use dynamic routing or a static route back to the Cisco IOS router to establish the peer relationship.

Explanation

On IOS XR, a BFD session comes up only after the peer’s address is reachable in the RIB. That reachability can be provided either by any dynamic routing protocol (OSPF, IS-IS, BGP, …) or by a static route. No particular signalling protocol (for example LDP) is required, and IOS XR interoperates with IOS BFD.

Why Incorrect

A. LDP is not a BFD prerequisite; only plain IP reachability is needed.
B. IOS XR supports IPv4 single-hop and multihop BFD (since release 3.9).
D. BFD packets use UDP and standardized formats, allowing interoperation between IOS XR and IOS.

References

1. Cisco IOS XR BFD Configuration Guide, Rel 7.3.x – “BFD Session Requirements”, para 1 (route must exist via dynamic or static).

2. Cisco IOS XR Software System Architectures—BFD, p. 9.

3. RFC 5880 – Bidirectional Forwarding Detection, Sec 1 (protocol interoperability).

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