ICND2: Interconnecting Cisco Networking Devices Part 2 (legacy) — Question 7

After you configure a GRE tunnel between two networks, the tunnel comes up normally, but workstations on each side of the tunnel cannot communicate. Which reason for the problem is most likely true?

Answer options

• A. The tunnel source address is incorrect.
• B. The tunnel destination address is incorrect.
• C. The route between the networks is undefined.
• D. The IP MTU is incorrect.
• E. The distance configuration is missing.

Correct answer: D

Explanation

The correct answer is D because an incorrect IP MTU can lead to packet fragmentation issues, preventing communication between the networks over the GRE tunnel. Options A and B relate to address issues, which would typically prevent the tunnel from coming up at all. Option C indicates a routing problem that would affect connectivity but does not directly relate to communication through an established tunnel. Option E is not relevant to GRE tunnel operation.