300-410 IPv6 Tunneling Techniques Practice Question
This 300-410 practice question tests your understanding of ipv6 tunneling techniques. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
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?
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.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Related concept
Read the scenario before looking for a memorised answer.
✗
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
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.
Detailed technical explanation
How to think about this question
In 6rd (RFC 5969), the customer's delegated IPv6 prefix is computed by concatenating the 6rd prefix (e.g., 2001:DB8::/32) with the customer's IPv4 address (e.g., 192.0.2.1 = 0xC0000201), resulting in a /64 prefix like 2001:DB8:C000:201::/64. The BR must have a route for this specific delegated prefix pointing to the customer's IPv4 address; without it, the BR cannot encapsulate return traffic. This is a common misconfiguration where the BR is not statically or dynamically aware of the customer's delegated prefix, even though the 6rd tunnel itself is up.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the 300-410 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
IPv6 Tunneling Techniques — This question tests IPv6 Tunneling Techniques — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: 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.
What should I do if I get this 300-410 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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