hardMultiple ChoiceObjective-mapped
300-410 Practice Question: An engineer configures a 6rd tunnel on a router
An engineer configures a 6rd tunnel on a router. The tunnel comes up and the router can reach IPv6 hosts on the 6rd domain, but IPv6 hosts behind the router cannot reach the internet (native IPv6). The 6rd border relay is configured correctly. What is the most likely cause?
⚠ Common exam trap
Cisco often tests the nuance that a tunnel being up and reachable within the 6rd domain does not imply a default route exists for native IPv6 internet access, leading candidates to overlook the missing static route.
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 6rd router does not have a default route pointing to the tunnel interface; a static route to ::/0 via the tunnel is required.
The 6rd tunnel is up and the router can reach IPv6 hosts on the 6rd domain, but native IPv6 hosts behind the router cannot reach the internet. This indicates that the tunnel encapsulation works, but return traffic from the native IPv6 internet cannot reach the hosts because the router lacks a default route pointing to the tunnel interface. A static route to ::/0 via the tunnel interface is required to forward all non-6rd IPv6 traffic to the border relay, which then encapsulates it for the native IPv6 internet.
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 6rd router does not have a default route pointing to the tunnel interface; a static route to ::/0 via the tunnel is required.
Why this is correct
6rd does not automatically install a default route. Without a default route via the tunnel, traffic to native IPv6 destinations is dropped.
- ✗
The 6rd prefix length is incorrect; it must be /32 for the tunnel to work.
Why it's wrong here
6rd prefix length can vary; it is not fixed to /32.
- ✗
The border relay is not configured with the same 6rd prefix.
Why it's wrong here
If the border relay were misconfigured, the tunnel would not come up.
- ✗
The router's IPv4 address is not in the 6rd delegated prefix range.
Why it's wrong here
The 6rd prefix is derived from the IPv4 address; if it were out of range, the tunnel would not form.
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JA
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.