350-401 Question 532
Single answerIn a DMVPN Phase 2 deployment, a network engineer observes that spoke-to-spoke communication is not occurring as expected, and all traffic is being routed through the hub. What is the most likely cause of this behavior?
- A
The spokes are not configured with the 'ip nhrp shortcut' command.
- B
The hub router does not have a static route to the spoke networks.
- C
The NHRP authentication keys are mismatched between the spokes.
- D
The 'ip nhrp map multicast' command is missing on the spoke routers.
Show answer and explanation
Correct answer: A
Explanation
In DMVPN Phase 2, spoke-to-spoke communication requires the 'ip nhrp shortcut' command on the spoke routers. This command allows the spokes to dynamically learn and establish direct tunnels to each other via NHRP, bypassing the hub for data traffic. Without this configuration, spokes will always route traffic through the hub, which is not the desired behavior in Phase 2.
- A. Correct.
Correct. The 'ip nhrp shortcut' command is required on the spoke routers to enable spoke-to-spoke communication in DMVPN Phase 2. Without this configuration, traffic defaults to routing through the hub.
- B. Incorrect.
Incorrect. The hub router does not need a static route to the spoke networks for spoke-to-spoke communication in DMVPN Phase 2. The NHRP protocol dynamically resolves spoke-to-spoke next hops.
- C. Incorrect.
Incorrect. While mismatched NHRP authentication keys can cause communication issues, it would typically prevent all NHRP communications, not just spoke-to-spoke traffic.
- D. Incorrect.
Incorrect. The 'ip nhrp map multicast' command is used to support multicast traffic (e.g., routing protocols) in DMVPN. It does not directly impact spoke-to-spoke unicast traffic.