mediumMultiple ChoiceObjective-mapped
300-410 Practice Question: Given this configuration on Router R6: ```…
Given this configuration on Router R6: ```
interface Tunnel0
ipv6 address 2001:DB8:8::1/64 tunnel source 2001:DB8:9::1 tunnel destination 2001:DB8:10::2 tunnel mode gre ipv6 tunnel path-mtu-discovery ``` What is the effect?
⚠ Common exam trap
Cisco often tests the misconception that path-mtu-discovery is unsupported with GRE tunnels, but it is actually supported and commonly used to avoid fragmentation in overlay networks.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The tunnel will dynamically adjust the MTU based on the path MTU discovery.
The `tunnel path-mtu-discovery` command enables Path MTU Discovery (PMTUD) for the GRE tunnel, which dynamically determines the maximum MTU along the path to the tunnel destination and adjusts the tunnel interface's MTU accordingly. This prevents fragmentation issues by allowing the tunnel to use the smallest MTU in the path. Option B correctly identifies this behavior.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The tunnel will not work because path-mtu-discovery is not supported with GRE.
Why it's wrong here
Path MTU discovery is supported with GRE tunnels.
- ✓
The tunnel will dynamically adjust the MTU based on the path MTU discovery.
Why this is correct
The 'tunnel path-mtu-discovery' command enables PMTUD for the tunnel.
- ✗
The tunnel mode should be 'ipv6ip' for IPv6 transport.
Why it's wrong here
GRE over IPv6 is correctly configured; ipv6ip is for IPv4 transport.
- ✗
The tunnel source and destination must be IPv4 addresses.
Why it's wrong here
For gre ipv6, source and destination are IPv6.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.