- A
An IPv6 access list on the router is blocking Router Advertisement messages.
Why wrong: An access list could block ICMPv6 Router Advertisements, preventing hosts from obtaining prefixes and global unicast addresses. However, this does not explain why the router's own interface lacks a global unicast address when statically configured or when the router itself should be generating RAs. The missing ipv6 unicast-routing command is a more fundamental cause.
- B
IPv6 unicast routing has not been enabled on the router.
The ipv6 unicast-routing command is required to enable IPv6 forwarding on Cisco routers. Without it, the router does not participate in IPv6 routing, does not generate Router Advertisements, and interfaces will not obtain global unicast addresses through SLAAC or DHCPv6 relay. The show ipv6 interface output displaying only a link-local address, combined with the absence of ipv6 unicast-routing in the configuration, confirms this root cause.
- C
The IPv4 resource is not configured for NAT64 translation.
Why wrong: While NAT64 is a common method for IPv6-only hosts to access IPv4 resources, the symptom explicitly shows a missing global unicast address on the router interface and a missing ipv6 unicast-routing command. This indicates a basic IPv6 routing failure, not a translation service configuration issue.
- D
The host has an incorrect default gateway for IPv6.
Why wrong: A misconfigured default gateway on the host would prevent it from reaching off-link resources. However, the technician observed a missing global unicast address on the router interface and the absence of ipv6 unicast-routing, indicating that the router itself is not properly configured for IPv6 routing. The host's gateway issue would be a consequence, not the root cause.
Quick Answer
The answer is that the missing `ipv6 unicast-routing` command is the most likely cause, because without it the router does not function as an IPv6 router and therefore does not send Router Advertisement messages. These RAs are essential for stateless address autoconfiguration (SLAAC); without them, the IPv6-only host cannot generate a global unicast address or learn a default gateway, breaking its ability to reach any IPv4 resource even if NAT64 is configured. On the CCNA 200-301 v2 exam, this question tests your understanding of the IPv6 neighbor discovery process and the router’s role in SLAAC—a common trap is assuming a link-local address alone is sufficient for global connectivity. Remember the memory tip: “No unicast-routing, no RA, no global address.”
CCNA Network Infrastructure and Connectivity Practice Question
This 200-301 practice question tests your understanding of network infrastructure and connectivity. 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 technician is troubleshooting a dual-stack network where an IPv6-only host cannot reach an IPv4 resource. The technician issues the show ipv6 interface brief command on the local router and notices the interface facing the host has a link-local address but no global unicast address. The technician then checks the running configuration and finds that the command ipv6 unicast-routing is missing. 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
IPv6 unicast routing has not been enabled on the router.
The missing `ipv6 unicast-routing` command means the router is not acting as an IPv6 router, so it does not send Router Advertisement (RA) messages. Without RAs, the host cannot autoconfigure a global unicast address or learn a default gateway, breaking IPv6 connectivity to any IPv4 resource even if NAT64 is present.
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.
- ✗
An IPv6 access list on the router is blocking Router Advertisement messages.
Why it's wrong here
An access list could block ICMPv6 Router Advertisements, preventing hosts from obtaining prefixes and global unicast addresses. However, this does not explain why the router's own interface lacks a global unicast address when statically configured or when the router itself should be generating RAs. The missing ipv6 unicast-routing command is a more fundamental cause.
- ✓
IPv6 unicast routing has not been enabled on the router.
Why this is correct
The ipv6 unicast-routing command is required to enable IPv6 forwarding on Cisco routers. Without it, the router does not participate in IPv6 routing, does not generate Router Advertisements, and interfaces will not obtain global unicast addresses through SLAAC or DHCPv6 relay. The show ipv6 interface output displaying only a link-local address, combined with the absence of ipv6 unicast-routing in the configuration, confirms this root cause.
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 IPv4 resource is not configured for NAT64 translation.
Why it's wrong here
While NAT64 is a common method for IPv6-only hosts to access IPv4 resources, the symptom explicitly shows a missing global unicast address on the router interface and a missing ipv6 unicast-routing command. This indicates a basic IPv6 routing failure, not a translation service configuration issue.
- ✗
The host has an incorrect default gateway for IPv6.
Why it's wrong here
A misconfigured default gateway on the host would prevent it from reaching off-link resources. However, the technician observed a missing global unicast address on the router interface and the absence of ipv6 unicast-routing, indicating that the router itself is not properly configured for IPv6 routing. The host's gateway issue would be a consequence, not the root cause.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓IPv6 unicast routing has not been enabled on the router.Correct answer▾
Why this is correct
The ipv6 unicast-routing command is required to enable IPv6 forwarding on Cisco routers. Without it, the router does not participate in IPv6 routing, does not generate Router Advertisements, and interfaces will not obtain global unicast addresses through SLAAC or DHCPv6 relay. The show ipv6 interface output displaying only a link-local address, combined with the absence of ipv6 unicast-routing in the configuration, confirms this root cause.
✗An IPv6 access list on the router is blocking Router Advertisement messages.Wrong answer — click to see why▾
Why this is wrong here
This option focuses on a filtering issue, not the disabled routing engine, and would not cause the router’s own interface to lack a global unicast address.
✗The IPv4 resource is not configured for NAT64 translation.Wrong answer — click to see why▾
Why this is wrong here
NAT64 configuration would affect translation, but the root cause visible in the output is the lack of IPv6 routing capability on the router.
✗The host has an incorrect default gateway for IPv6.Wrong answer — click to see why▾
Why this is wrong here
This shifts the blame to the host, but the router-side evidence (missing command and missing global unicast) clearly indicates a router configuration problem.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that configuring an IPv6 address on an interface is sufficient for IPv6 routing, when in fact the global `ipv6 unicast-routing` command is required to enable the router to forward IPv6 packets and send Router Advertisements.
Trap categories for this question
Command / output trap
An access list could block ICMPv6 Router Advertisements, preventing hosts from obtaining prefixes and global unicast addresses. However, this does not explain why the router's own interface lacks a global unicast address when statically configured or when the router itself should be generating RAs. The missing ipv6 unicast-routing command is a more fundamental cause.
Detailed technical explanation
How to think about this question
The `ipv6 unicast-routing` command globally enables IPv6 forwarding on the router, which is a prerequisite for the router to originate Router Advertisements (per RFC 4861). Without this command, even if interfaces have IPv6 addresses configured, the router will not respond to Neighbor Solicitations for the all-routers multicast address or send periodic RAs, leaving hosts unable to perform Stateless Address Autoconfiguration (SLAAC) or learn a default route. In a dual-stack scenario, this often manifests as the host having only a link-local address and no reachability beyond the local link.
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.
- →
Network Infrastructure and Connectivity — study guide chapter
Learn the concepts, then practise the questions
- →
Network Infrastructure and Connectivity practice questions
Targeted practice on this topic area only
- →
All 200-301 questions
1,819 questions across all exam domains
- →
CCNA 200-301 v2 study guide
Full concept coverage aligned to exam objectives
- →
200-301 practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Related 200-301 practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Network Infrastructure and Connectivity practice questions
Practise 200-301 questions linked to Network Infrastructure and Connectivity.
Switching and Network Access practice questions
Practise 200-301 questions linked to Switching and Network Access.
IP Routing practice questions
Practise 200-301 questions linked to IP Routing.
Network Services and Security practice questions
Practise 200-301 questions linked to Network Services and Security.
AI and Network Operations practice questions
Practise 200-301 questions linked to AI and Network Operations.
CCNA subnetting practice questions
Practise IPv4 subnetting, CIDR, masks, host ranges and subnet selection.
CCNA OSPF practice questions
Practise OSPF neighbours, router IDs, metrics, areas and routing-table interpretation.
CCNA VLAN practice questions
Practise VLANs, access ports, trunks, allowed VLANs and switching scenarios.
CCNA STP practice questions
Practise spanning tree, root bridge election, port roles and STP troubleshooting.
CCNA EtherChannel practice questions
Practise LACP, PAgP, port-channel behaviour and bundle requirements.
CCNA ACL practice questions
Practise standard and extended ACLs, permit/deny logic and traffic filtering.
CCNA NAT practice questions
Practise static NAT, dynamic NAT, PAT and inside/outside address translation.
Practice this exam
Start a free 200-301 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 200-301 question test?
Network Infrastructure and Connectivity — This question tests Network Infrastructure and Connectivity — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: IPv6 unicast routing has not been enabled on the router. — The missing `ipv6 unicast-routing` command means the router is not acting as an IPv6 router, so it does not send Router Advertisement (RA) messages. Without RAs, the host cannot autoconfigure a global unicast address or learn a default gateway, breaking IPv6 connectivity to any IPv4 resource even if NAT64 is present.
What should I do if I get this 200-301 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 →
Last reviewed: Jun 25, 2026
This 200-301 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 200-301 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.