Question 303 of 2,152

IPv6 Tunneling Techniques →mediumMultiple ChoiceObjective-mapped

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 network engineer is troubleshooting an IPv6 over IPv4 tunnel using Teredo on a Windows host. The host can access some IPv6 resources on the internet but cannot reach a specific internal IPv6 server. The engineer suspects the Teredo relay is misconfigured. What is the most likely issue?

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.

Question 1mediummultiple choice

Study the full IPv6 explanation →

A
The Teredo relay is not in the same IPv4 network as the host, or the relay does not have a route to the internal IPv6 server.
Correct because the Teredo relay must be able to forward packets to the destination IPv6 network. If the relay lacks a route, traffic will be dropped.
B
The host's firewall is blocking Teredo traffic on UDP port 3544.
Why wrong: Incorrect because the host can access some IPv6 resources, so Teredo is working for those destinations; the issue is specific to the internal server.
C
The internal server is not configured with an IPv6 address.
Why wrong: Incorrect because the server is reachable via other means (e.g., IPv4), but the question states the host cannot reach it via IPv6.
D
The Teredo client on the host is using an incorrect server.
Why wrong: Incorrect because the Teredo server is used for address assignment, not for forwarding traffic to native IPv6 networks.

Full breakdown with real-world context →

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 Teredo relay is not in the same IPv4 network as the host, or the relay does not have a route to the internal IPv6 server.

Teredo relays are responsible for forwarding traffic between the Teredo IPv6 tunnel and the native IPv6 network. If the relay is not on the same IPv4 subnet as the host or lacks a route to the internal IPv6 server, the host can reach public IPv6 resources (via other relays) but fails to reach the internal server. This matches the symptom of partial connectivity.

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 Teredo relay is not in the same IPv4 network as the host, or the relay does not have a route to the internal IPv6 server.
Why this is correct
Correct because the Teredo relay must be able to forward packets to the destination IPv6 network. If the relay lacks a route, traffic will be dropped.
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 firewall is blocking Teredo traffic on UDP port 3544.
Why it's wrong here
Incorrect because the host can access some IPv6 resources, so Teredo is working for those destinations; the issue is specific to the internal server.
✗
The internal server is not configured with an IPv6 address.
Why it's wrong here
Incorrect because the server is reachable via other means (e.g., IPv4), but the question states the host cannot reach it via IPv6.
✗
The Teredo client on the host is using an incorrect server.
Why it's wrong here
Incorrect because the Teredo server is used for address assignment, not for forwarding traffic to native IPv6 networks.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the distinction between Teredo relay and Teredo server roles, and the trap here is that candidates confuse a misconfigured relay (which affects specific destinations) with a misconfigured server (which breaks all Teredo connectivity).

Detailed technical explanation

How to think about this question

Teredo uses a relay (typically an anycast address 2001:0000::/32) to encapsulate IPv6 packets in IPv4 UDP datagrams. The relay must have a native IPv6 route to the destination; if the internal server is on a private IPv6 subnet not advertised to the relay, packets are dropped. This is common in enterprise networks where internal IPv6 prefixes are not globally routable.

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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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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 Teredo relay is not in the same IPv4 network as the host, or the relay does not have a route to the internal IPv6 server. — Teredo relays are responsible for forwarding traffic between the Teredo IPv6 tunnel and the native IPv6 network. If the relay is not on the same IPv4 subnet as the host or lacks a route to the internal IPv6 server, the host can reach public IPv6 resources (via other relays) but fails to reach the internal server. This matches the symptom of partial connectivity.

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.

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