350-401 Question 509
Single answerAn enterprise is configuring a DMVPN single-hub topology to connect its branch offices. The hub router is configured with the following partial NHRP configuration:
interface Tunnel0
ip address 10.1.1.1 255.255.255.0
tunnel source GigabitEthernet0/0
tunnel mode gre multipoint
ip nhrp network-id 1
ip nhrp authentication securekey
ip nhrp map multicast dynamic
After completing the corresponding configuration on the spoke routers, the spoke routers cannot establish connectivity with the hub. What additional configuration is required on the hub router to resolve this issue?
- A
Configure 'ip nhrp map
' on the hub router - B
Add 'ip nhrp redirect' to the Tunnel0 interface configuration
- C
Enable the 'ip nhrp short-path' command on the hub router
- D
Ensure the hub router has a default route to reach the spoke routers' public IPs
Show answer and explanation
Correct answer: B
Explanation
In a DMVPN single-hub topology, the 'ip nhrp redirect' command is necessary on the hub to enable dynamic NHRP resolution and inform spoke routers of the hub's role in managing traffic flow. Without this command, the spoke routers cannot establish proper communication with the hub, leading to connectivity issues. The other options are either not required or irrelevant in this scenario.
- A. Incorrect.
This command is not needed on the hub, as the 'ip nhrp map' configuration is typically used on spoke routers to statically map the spoke's public and private IP addresses. In a single-hub DMVPN, this is not required on the hub for dynamic mapping.
- B. Correct.
The 'ip nhrp redirect' command is required on the hub router in single-hub DMVPN setups to inform spoke routers of the hub's role in facilitating dynamic spoke-to-spoke communication.
- C. Incorrect.
The 'ip nhrp short-path' command is not valid in this context. It does not exist as a configuration command and is not related to DMVPN operation.
- D. Incorrect.
While a default route is essential for the hub router to communicate with the spokes, the issue described in the question pertains to NHRP configuration, not route reachability.