- A
Router B is missing a static route pointing the local IPv6 prefix to the tunnel interface.
Correct because without a return route, Router B cannot forward packets destined to the local prefix, breaking bidirectional communication.
- B
The tunnel mode is set to 'ipv6ip 6to4' instead of 'ipv6ip'.
Why wrong: Incorrect because 'tunnel mode ipv6ip' is correct for manual tunnels; 6to4 mode would change the encapsulation and addressing.
- C
The tunnel source on Router B is misconfigured with the wrong IPv4 address.
Why wrong: Incorrect because if the tunnel is up and they can ping each other's tunnel IPv6 addresses, the tunnel source is correct.
- D
The IPv6 access-list on Router B is blocking incoming traffic from the local prefix.
Why wrong: Incorrect because the issue is routing, not filtering; the engineer should check the routing table first.
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 a manual IPv6-in-IPv4 tunnel between two Cisco routers. The tunnel is up, and both routers can ping each other's tunnel IPv6 addresses. However, traffic from a host behind Router A to a host behind Router B fails. The engineer notices that Router A has a route to the remote IPv6 prefix via the tunnel, but Router B does not have a route to the local IPv6 prefix. 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
Router B is missing a static route pointing the local IPv6 prefix to the tunnel interface.
The tunnel is up and both routers can ping each other's tunnel IPv6 addresses, confirming that the tunnel itself is operational. However, traffic from a host behind Router A to a host behind Router B fails because Router B lacks a route back to the local IPv6 prefix (the network behind Router A). For bidirectional communication, both routers must have a route to the remote IPv6 prefix pointing to the tunnel interface. Since Router B is missing this static route, it cannot forward return traffic into the tunnel, causing the failure.
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.
- ✓
Router B is missing a static route pointing the local IPv6 prefix to the tunnel interface.
Why this is correct
Correct because without a return route, Router B cannot forward packets destined to the local prefix, breaking bidirectional communication.
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 tunnel mode is set to 'ipv6ip 6to4' instead of 'ipv6ip'.
Why it's wrong here
Incorrect because 'tunnel mode ipv6ip' is correct for manual tunnels; 6to4 mode would change the encapsulation and addressing.
- ✗
The tunnel source on Router B is misconfigured with the wrong IPv4 address.
Why it's wrong here
Incorrect because if the tunnel is up and they can ping each other's tunnel IPv6 addresses, the tunnel source is correct.
- ✗
The IPv6 access-list on Router B is blocking incoming traffic from the local prefix.
Why it's wrong here
Incorrect because the issue is routing, not filtering; the engineer should check the routing table first.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between tunnel reachability (Layer 3 connectivity between tunnel endpoints) and prefix reachability (routing of actual user networks), leading candidates to overlook the missing static route on the return path.
Detailed technical explanation
How to think about this question
In a manual IPv6-in-IPv4 tunnel (RFC 4213), the tunnel interface acts as a point-to-point link, and each router must have a static route (or dynamic route) pointing the remote IPv6 prefix to the tunnel interface. Without this route, the router has no path to forward packets destined for the remote prefix, even though the tunnel itself is up. This is a common misconfiguration where the tunnel is established but routing is incomplete, often verified by checking 'show ipv6 route' on both routers.
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 security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
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.
- →
IPv6 Tunneling Techniques — study guide chapter
Learn the concepts, then practise the questions
- →
IPv6 Tunneling Techniques practice questions
Targeted practice on this topic area only
- →
All 300-410 questions
2,152 questions across all exam domains
- →
Cisco CCNP ENARSI 300-410 study guide
Full concept coverage aligned to exam objectives
- →
300-410 practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Related 300-410 practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Layer 3 Technologies practice questions
Practise 300-410 questions linked to Layer 3 Technologies.
EIGRP Troubleshooting practice questions
Practise 300-410 questions linked to EIGRP Troubleshooting.
OSPF Troubleshooting (v2/v3) practice questions
Practise 300-410 questions linked to OSPF Troubleshooting (v2/v3).
BGP Troubleshooting practice questions
Practise 300-410 questions linked to BGP Troubleshooting.
Route Redistribution practice questions
Practise 300-410 questions linked to Route Redistribution.
Policy-Based Routing (PBR) practice questions
Practise 300-410 questions linked to Policy-Based Routing (PBR).
VRF-Lite practice questions
Practise 300-410 questions linked to VRF-Lite.
Route Maps and Route Filtering practice questions
Practise 300-410 questions linked to Route Maps and Route Filtering.
Administrative Distance practice questions
Practise 300-410 questions linked to Administrative Distance.
Route Summarization practice questions
Practise 300-410 questions linked to Route Summarization.
Bidirectional Forwarding Detection (BFD) practice questions
Practise 300-410 questions linked to Bidirectional Forwarding Detection (BFD).
VPN Technologies practice questions
Practise 300-410 questions linked to VPN Technologies.
Practice this exam
Start a free 300-410 practice session
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
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: Router B is missing a static route pointing the local IPv6 prefix to the tunnel interface. — The tunnel is up and both routers can ping each other's tunnel IPv6 addresses, confirming that the tunnel itself is operational. However, traffic from a host behind Router A to a host behind Router B fails because Router B lacks a route back to the local IPv6 prefix (the network behind Router A). For bidirectional communication, both routers must have a route to the remote IPv6 prefix pointing to the tunnel interface. Since Router B is missing this static route, it cannot forward return traffic into the tunnel, causing the failure.
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 →
Keep practising
More 300-410 practice questions
- Drag and drop the steps to negotiate an IKEv2 IPsec site-to-site tunnel into the correct order, from first to last.
- Drag and drop the steps to troubleshoot an IPsec site-to-site VPN adjacency failure into the correct order, from first t…
- Drag and drop the steps to verify and validate the operational state of an IPsec site-to-site VPN into the correct order…
- Drag and drop the steps to configure a GRE tunnel for IPv6 over IPv4 into the correct order, from first to last.
- Drag and drop the steps to troubleshoot IPv6 over IPv4 tunnel adjacency or connectivity failures into the correct order,…
- Drag and drop the steps to verify and validate the operational state of an IPv6 tunneling technique into the correct ord…
Last reviewed: Jun 24, 2026
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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.