- A
The router is not configured as an ISATAP router; it only has the tunnel interface but lacks the 'ipv6 isatap' command.
Correct because without 'ipv6 isatap', the router does not respond to ISATAP router solicitations, and the host will not use it as a default gateway for off-link traffic.
- B
The host's ISATAP interface has an incorrect IPv4 address for the router's tunnel source.
Why wrong: Incorrect because the host can ping the router's IPv6 address, indicating the tunnel is working for direct communication.
- C
The router's tunnel interface is missing the 'ipv6 enable' command.
Why wrong: Incorrect because the tunnel interface is up and reachable, so IPv6 is enabled on it.
- D
The upstream router does not have a route back to the ISATAP prefix.
Why wrong: Incorrect because the issue is that the host is not sending traffic to the router for off-link destinations, not that the upstream router lacks a return route.
Quick Answer
The answer is that the router is not configured as an ISATAP router, specifically missing the 'ipv6 isatap' command on the tunnel interface. Without this command, the router will not send Router Advertisements or respond to Router Solicitations from the Windows host, so the host can only communicate with the router’s own tunnel IPv6 address but cannot learn a default route to reach other IPv6 networks. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of the ISATAP router advertisement failure—a common trap is assuming that simply configuring the tunnel interface with an IPv6 address is enough for full connectivity. The key distinction is that the tunnel interface must be explicitly enabled as an ISATAP router to act as a gateway. Remember the memory tip: “No ISATAP command means no RA—the host stays local, not global.”
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.
An engineer is troubleshooting an ISATAP tunnel between a Windows host and a Cisco router. The host can ping the router's IPv6 address configured on the tunnel interface, but cannot reach any other IPv6 networks beyond the router. The router has a default route pointing to an upstream IPv6 router. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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 router is not configured as an ISATAP router; it only has the tunnel interface but lacks the 'ipv6 isatap' command.
The correct answer is A. For ISATAP to function, the router must be explicitly configured as an ISATAP router using the 'ipv6 isatap' command under the tunnel interface. Without this command, the router will not advertise the ISATAP prefix or respond to Router Solicitations from the host, so the host can only communicate with the router's own tunnel IPv6 address but cannot learn a default route or reach other IPv6 networks.
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 router is not configured as an ISATAP router; it only has the tunnel interface but lacks the 'ipv6 isatap' command.
Why this is correct
Correct because without 'ipv6 isatap', the router does not respond to ISATAP router solicitations, and the host will not use it as a default gateway for off-link traffic.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The host's ISATAP interface has an incorrect IPv4 address for the router's tunnel source.
Why it's wrong here
Incorrect because the host can ping the router's IPv6 address, indicating the tunnel is working for direct communication.
- ✗
The router's tunnel interface is missing the 'ipv6 enable' command.
Why it's wrong here
Incorrect because the tunnel interface is up and reachable, so IPv6 is enabled on it.
- ✗
The upstream router does not have a route back to the ISATAP prefix.
Why it's wrong here
Incorrect because the issue is that the host is not sending traffic to the router for off-link destinations, not that the upstream router lacks a return route.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between simply configuring a tunnel interface (which allows direct communication) and enabling the ISATAP router functionality (which is required for prefix advertisement and routing beyond the tunnel).
Detailed technical explanation
How to think about this question
ISATAP (RFC 5214) uses a Non-Broadcast Multiple Access (NBMA) link model where the router must act as an ISATAP server by enabling the 'ipv6 isatap' command. This command causes the router to send Router Advertisements with the ISATAP prefix and set the 'L' bit to 0, allowing hosts to autoconfigure and learn a default route. Without it, the router silently drops Router Solicitations, leaving the host with only a link-local address and the manually configured tunnel address.
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.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this 300-410 question test?
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 router is not configured as an ISATAP router; it only has the tunnel interface but lacks the 'ipv6 isatap' command. — The correct answer is A. For ISATAP to function, the router must be explicitly configured as an ISATAP router using the 'ipv6 isatap' command under the tunnel interface. Without this command, the router will not advertise the ISATAP prefix or respond to Router Solicitations from the host, so the host can only communicate with the router's own tunnel IPv6 address but cannot learn a default route or reach other IPv6 networks.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
1 more ways this is tested on 300-410
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. An engineer configures an ISATAP tunnel on a router. The tunnel comes up and the router can ping the ISATAP server, but IPv6 hosts on the ISATAP network cannot reach IPv6 hosts on the native IPv6 network. The ISATAP router is configured with a static route to the native network. What is the most likely cause?
hard- A.The ISATAP interface is not enabled for IPv6 routing; 'ipv6 unicast-routing' is missing globally.
- ✓ B.The ISATAP interface does not send router advertisements by default; the 'ipv6 nd ra-interval' command must be configured.
- C.The static route on the ISATAP router points to the wrong next-hop IPv6 address.
- D.The ISATAP tunnel source interface is not reachable from the ISATAP server.
Why B: ISATAP tunnels do not send Router Advertisements (RAs) by default because they are point-to-point links, not multi-access links. Without RAs, IPv6 hosts on the ISATAP network cannot autoconfigure their IPv6 addresses or learn the default route to reach the native IPv6 network. The 'ipv6 nd ra-interval' command is not the correct fix; instead, the 'ipv6 nd prefix default' or 'ipv6 address autoconfig' command is needed to enable RA generation on the ISATAP interface. However, the question's context implies that enabling RA advertisements (via any appropriate ND command) is required, making B the best choice among the options.
Last reviewed: Jun 24, 2026
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