350-401 Question 535
Single answerAn enterprise network is configured with a DMVPN topology. The hub router is successfully facilitating communication between spoke routers. However, direct spoke-to-spoke communication is not working. What is the most likely reason for this issue?
- A
The spoke routers are configured with 'ip nhrp map multicast dynamic'.
- B
The NHRP shortcuts are not enabled on the spoke routers.
- C
The spoke routers do not have a default route pointing to the hub router.
- D
The spoke routers are configured with 'ip nhrp redirect' instead of 'ip nhrp shortcut'.
Show answer and explanation
Correct answer: B
Explanation
In a DMVPN environment, spoke-to-spoke communication depends on NHRP shortcuts, which allow spoke routers to dynamically learn and establish direct tunnels to other spokes. If NHRP shortcuts are not enabled, spoke traffic will always be routed through the hub router, preventing direct communication. Configuring 'ip nhrp shortcut' on the spokes resolves this issue.
- A. Incorrect.
This is a correct configuration and does not prevent spoke-to-spoke communication. The 'ip nhrp map multicast dynamic' command allows multicast traffic, but it is unrelated to NHRP shortcuts required for direct spoke-to-spoke traffic.
- B. Correct.
Correct. The absence of NHRP shortcuts on spoke routers would prevent them from establishing direct tunnels for spoke-to-spoke communication, as the shortcuts are essential for determining dynamic routes between spokes.
- C. Incorrect.
While a default route pointing to the hub router is necessary for initial communication, it is unrelated to enabling direct spoke-to-spoke communication. Spoke-to-spoke traffic relies on NHRP shortcuts.
- D. Incorrect.
The 'ip nhrp redirect' command is configured on the hub router, not on the spoke routers. Misconfiguring this on spokes would not directly address the issue of enabling spoke-to-spoke communication.