300-440 Question 178
Single answerAn organization is implementing a multipoint GRE (mGRE) tunnel on a hub-and-spoke topology to enable dynamic tunneling between branch offices. After configuring the mGRE interface on the hub router, you notice that traffic is not being forwarded to the spokes. Upon reviewing the configuration, which additional step should be taken to ensure proper functionality of the mGRE tunnel?
- A
Configure NHRP (Next Hop Resolution Protocol) on the hub router.
- B
Enable IP multicast routing on the hub router.
- C
Apply a static GRE tunnel destination on the hub router.
- D
Increase the MTU size on the mGRE interface.
Show answer and explanation
Correct answer: A
Explanation
In a hub-and-spoke topology using mGRE, dynamic resolution of tunnel endpoints is required. This is achieved by configuring NHRP on the hub router, allowing the hub to resolve and communicate with the dynamically defined spokes. Without NHRP, the mGRE tunnel cannot function correctly in a dynamic environment, which leads to traffic forwarding issues.
- A. Correct.
Correct. NHRP (Next Hop Resolution Protocol) is required to resolve dynamic tunnel endpoints and is an essential component for mGRE functionality in a dynamic environment like a hub-and-spoke topology.
- B. Incorrect.
Incorrect. While IP multicast routing can be useful in certain scenarios, it is not a requirement for basic mGRE tunnel functionality.
- C. Incorrect.
Incorrect. Static GRE tunnel destinations are not used in mGRE configurations, as mGRE is designed for dynamic tunnels.
- D. Incorrect.
Incorrect. Increasing the MTU size on the mGRE interface is not necessary for basic mGRE functionality and would not resolve the traffic forwarding issue.