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300-410 Practice Question: A service provider is using 6rd (IPv6 Rapid…
A service provider is using 6rd (IPv6 Rapid Deployment) tunnels to provide IPv6 to customers. Customer router R1 has the following relevant configuration: interface Tunnel0 ipv6 address 2001:DB8:1::1/64 tunnel source 192.0.2.1 tunnel mode ipv6ip 6rd ipv6 6rd prefix 2001:DB8::/32 6rd-br 198.51.100.1. Router R2 (BR) shows: R2# show ipv6 route 2001:DB8:1::/64 % Route not found. What is the root cause?
⚠ Common exam trap
Cisco often tests the misconception that 6rd requires matching tunnel configurations on both ends, when in reality the BR only needs a route for the delegated prefix and does not run a 6rd tunnel interface itself.
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 prefix on R1 should match the BR's configured 6rd prefix, and the BR must have a route for the customer's delegated prefix.
The 6rd (IPv6 Rapid Deployment) tunnel requires both the customer router (R1) and the border relay (BR, R2) to agree on the same 6rd prefix. R1 is configured with prefix 2001:DB8::/32, but the BR has no route for the delegated prefix 2001:DB8:1::/64, which is derived from R1's IPv4 address (192.0.2.1) and the 6rd prefix. Without this route in the BR's IPv6 routing table, the BR cannot forward traffic to the customer's 6rd tunnel, causing the 'Route not found' error.
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 prefix on R1 should match the BR's configured 6rd prefix, and the BR must have a route for the customer's delegated prefix.
Why this is correct
The BR must have a route for the customer's IPv6 prefix, which is derived from the 6rd prefix and the customer's IPv4 address.
- ✗
The tunnel mode should be ipv6ip 6rd on both ends, but the BR is missing the 6rd configuration.
Why it's wrong here
The BR is configured as a border relay, but the route is missing.
- ✗
The customer's IPv4 address is not reachable from the BR.
Why it's wrong here
The issue is the IPv6 route, not IPv4 reachability.
- ✗
The 6rd prefix length should be /64 instead of /32.
Why it's wrong here
The 6rd prefix is typically /32, and the customer gets a /64 delegation.
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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.