300-410 Question 173
Single answerA network engineer is tasked with configuring a DMVPN (Dynamic Multipoint Virtual Private Network) using a single hub architecture. The engineer has successfully configured the hub router with NHRP (Next Hop Resolution Protocol) and GRE over IPsec. However, the spoke routers cannot communicate with each other directly. Which configuration step should the engineer review to allow direct spoke-to-spoke communication?
- A
Ensure the
ip nhrp map multicastcommand is configured on the hub router's tunnel interface. - B
Verify that the
ip nhrp network-idvalue matches on all routers within the DMVPN network. - C
Enable the
ip nhrp redirectcommand on the hub router's tunnel interface. - D
Ensure the spoke routers are configured with static routes for each other's private subnets.
Show answer and explanation
Correct answer: C
Explanation
For a single-hub DMVPN topology, the ip nhrp redirect command on the hub router is crucial for enabling direct spoke-to-spoke communication. When this command is active, the hub router informs the spokes about optimized routes, allowing them to bypass the hub and communicate directly. Without this configuration, all traffic between spokes would default to being routed through the hub.
- A. Incorrect.
This command is necessary for multicast traffic to traverse the tunnel but does not enable spoke-to-spoke communication. It is not relevant to resolving the issue in this scenario.
- B. Incorrect.
The
ip nhrp network-idis required to match across all devices in the DMVPN domain, but it does not directly enable spoke-to-spoke communication. The issue described suggests a different missing configuration. - C. Correct.
The
ip nhrp redirectcommand on the hub router is essential for enabling spoke-to-spoke communication. It instructs the hub to notify spoke routers about optimized paths for direct communication. - D. Incorrect.
Static routes are not required for DMVPN spoke-to-spoke communication because NHRP dynamically resolves next-hop information. Configuring static routes would be an unnecessary and inefficient approach.