300-440 Question 196
Single answerAn enterprise network uses a DMVPN design with multiple branch offices connected to a central hub router. Due to increased traffic between branch offices, the network administrator wants to enable spoke-to-spoke communication to optimize routing and reduce latency. Which configuration step is mandatory to allow dynamic spoke-to-spoke tunnels in this DMVPN network?
- A
Enable NHRP shortcut commands on the spoke routers.
- B
Configure GRE multipoint tunnels on the spoke routers.
- C
Set the DMVPN network to operate in Phase 2 or Phase 3 mode.
- D
Enable OSPF as the routing protocol between the hub and spoke routers.
Show answer and explanation
Correct answer: C
Explanation
To allow spoke-to-spoke tunnels in a DMVPN network, the network must operate in either Phase 2 or Phase 3 mode. In Phase 1, all traffic must pass through the hub, preventing direct communication between spokes. Phase 2 allows direct spoke-to-spoke tunnels based on NHRP, while Phase 3 enhances this with routing optimization. Therefore, configuring the DMVPN network to operate in Phase 2 or 3 is a mandatory step for enabling spoke-to-spoke communication.
- A. Incorrect.
NHRP shortcut commands are not required to enable spoke-to-spoke communication. These commands help with optimizing routing decisions, but they are not mandatory for the creation of dynamic tunnels.
- B. Incorrect.
GRE multipoint tunnels are typically configured on the hub router, not on the spoke routers. While necessary for the overall DMVPN operation, this step alone does not enable direct spoke-to-spoke communication.
- C. Correct.
DMVPN Phase 2 or Phase 3 mode is mandatory for dynamic spoke-to-spoke tunnels. Phase 1 does not support direct spoke-to-spoke communication because all traffic is routed through the hub.
- D. Incorrect.
While OSPF is a valid routing protocol for DMVPN, the choice of routing protocol does not inherently enable or disable spoke-to-spoke tunnels. The DMVPN phase configuration is the critical factor.