350-401 Question 520
Single answerAn enterprise network is deploying DMVPN with NHRP to support dynamic spoke-to-spoke communication. The engineer observes that the spokes are successfully registering with the hub, but direct communication between the spokes is failing. What could be the cause of this issue?
- A
The spoke routers are missing the 'ip nhrp redirect' command.
- B
The hub router is missing the 'ip nhrp shortcut' command.
- C
The spoke routers are missing the 'ip nhrp map' command for the hub.
- D
The hub router is missing the 'ip nhrp redirect' command.
Show answer and explanation
Correct answer: D
Explanation
In a DMVPN topology, the 'ip nhrp redirect' command on the hub router enables the hub to send NHRP redirect messages to spokes. These messages inform spoke routers that they can establish direct tunnels to other spokes for efficient spoke-to-spoke communication. Without this command, spoke-to-spoke traffic will always traverse the hub, and direct communication between spokes will fail.
- A. Incorrect.
This is incorrect. The 'ip nhrp redirect' command is not required on the spoke routers; it is configured on the hub router to enable spoke-to-spoke communication in DMVPN Phase 2 or 3.
- B. Incorrect.
This is incorrect. The 'ip nhrp shortcut' command is not needed on the hub router; it is used on spoke routers to allow them to establish direct tunnels to other spokes.
- C. Incorrect.
This is incorrect. The 'ip nhrp map' command is used to manually map the NHRP address to the NBMA address, but it is not necessary in this scenario since the spokes are dynamically registering with the hub.
- D. Correct.
This is correct. The 'ip nhrp redirect' command is required on the hub router to notify spoke routers that they can communicate directly with each other instead of routing traffic through the hub.