- A
The PC's default gateway address is in a different subnet than the PC's IPv6 address.
An IPv6 host only uses a default gateway if it is on the same subnet. Since 2001:db8:acad:2::1 is in a different /64 subnet than the PC's 2001:db8:acad:1::100/64, the host considers the gateway unreachable and cannot send traffic beyond the local link.
- B
The PC's IPv6 stack has a corrupted binding that prevents routing.
Why wrong: Corrupted bindings might cause intermittent issues but are not the most likely cause when the configuration shows a clear subnet mismatch. Additionally, the IPv6 stack would have to be specifically damaged to affect only routing while leaving local communication intact.
- C
The router's IPv6 routing table does not have a route back to the PC's subnet.
Why wrong: If the router did not have a route back, the PC could still send packets out to the router if the gateway is correct. Here, the PC cannot even reach the gateway because it is misconfigured. Also, IPv4 connectivity works normally, indicating the router has proper connectivity on the link.
- D
The DNS server for IPv6 resolution is misconfigured, causing all off-subnet traffic to fail.
Why wrong: DNS problems only prevent name resolution; they do not block direct IP connectivity. If the PC can ping an off-subnet destination's IPv6 address, it would still work. The symptom describes inability to access any resources, not just name-based ones.
Quick Answer
The answer is that the PC’s default gateway is in a different subnet than its own IPv6 address. This is because IPv6 hosts require the default gateway to be on the same on-link subnet; the PC’s address 2001:db8:acad:1::100/64 places it in the 2001:db8:acad:1::/64 subnet, while the gateway 2001:db8:acad:2::1 belongs to the 2001:db8:acad:2::/64 subnet, so the host cannot directly reach the gateway and all off-subnet traffic fails. On the CCNA 200-301 v2 exam, this concept tests your understanding of IPv6 neighbor discovery and the fundamental rule that a host will only consider a next-hop router if its address is within the same prefix—a common trap is assuming IPv6 behaves like IPv4, where a gateway in a different subnet might still work with proxy ARP. Remember the memory tip: “Same /64, or it’s dead to me”—if the gateway’s prefix doesn’t match the host’s, the host won’t even attempt to send packets to it.
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 network technician configures a Windows 10 PC with a static IPv6 address of 2001:db8:acad:1::100/64 and a default gateway of 2001:db8:acad:2::1. The PC can communicate with other hosts in the 2001:db8:acad:1::/64 subnet, but it cannot access any resources on other subnets, even though IPv4 connectivity through the same network works normally. What is the most likely reason for this 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.
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 PC's default gateway address is in a different subnet than the PC's IPv6 address.
The PC's IPv6 address is 2001:db8:acad:1::100/64, placing it in the 2001:db8:acad:1::/64 subnet. The configured default gateway is 2001:db8:acad:2::1, which belongs to the 2001:db8:acad:2::/64 subnet. For IPv6, a host will only consider a default gateway on the same link-local or on-link subnet; if the gateway address is not within the same /64 prefix as the host's address, the host cannot send packets to it directly, and all off-subnet traffic fails.
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 PC's default gateway address is in a different subnet than the PC's IPv6 address.
Why this is correct
An IPv6 host only uses a default gateway if it is on the same subnet. Since 2001:db8:acad:2::1 is in a different /64 subnet than the PC's 2001:db8:acad:1::100/64, the host considers the gateway unreachable and cannot send traffic beyond the local link.
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 PC's IPv6 stack has a corrupted binding that prevents routing.
Why it's wrong here
Corrupted bindings might cause intermittent issues but are not the most likely cause when the configuration shows a clear subnet mismatch. Additionally, the IPv6 stack would have to be specifically damaged to affect only routing while leaving local communication intact.
- ✗
The router's IPv6 routing table does not have a route back to the PC's subnet.
Why it's wrong here
If the router did not have a route back, the PC could still send packets out to the router if the gateway is correct. Here, the PC cannot even reach the gateway because it is misconfigured. Also, IPv4 connectivity works normally, indicating the router has proper connectivity on the link.
- ✗
The DNS server for IPv6 resolution is misconfigured, causing all off-subnet traffic to fail.
Why it's wrong here
DNS problems only prevent name resolution; they do not block direct IP connectivity. If the PC can ping an off-subnet destination's IPv6 address, it would still work. The symptom describes inability to access any resources, not just name-based ones.
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.
✓The PC's default gateway address is in a different subnet than the PC's IPv6 address.Correct answer▾
Why this is correct
An IPv6 host only uses a default gateway if it is on the same subnet. Since 2001:db8:acad:2::1 is in a different /64 subnet than the PC's 2001:db8:acad:1::100/64, the host considers the gateway unreachable and cannot send traffic beyond the local link.
✗The PC's IPv6 stack has a corrupted binding that prevents routing.Wrong answer — click to see why▾
Why this is wrong here
This is a less common and less specific cause; the symptom points directly to a misconfigured gateway address in a different subnet.
✗The router's IPv6 routing table does not have a route back to the PC's subnet.Wrong answer — click to see why▾
Why this is wrong here
This option assumes a routing problem on the router, but the scenario indicates the PC cannot send packets to its gateway, which points to host configuration, not routing tables.
✗The DNS server for IPv6 resolution is misconfigured, causing all off-subnet traffic to fail.Wrong answer — click to see why▾
Why this is wrong here
DNS misconfiguration would cause failures when using hostnames, but not for direct IP connectivity tests like pinging a remote IPv6 address.
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 concept that an IPv6 host will only use a default gateway that is within the same subnet (same /64 prefix) as its own configured IPv6 address, unlike IPv4 where a gateway in a different subnet can still be used if the host has a route to it.
Trap categories for this question
Command / output trap
Corrupted bindings might cause intermittent issues but are not the most likely cause when the configuration shows a clear subnet mismatch. Additionally, the IPv6 stack would have to be specifically damaged to affect only routing while leaving local communication intact.
Detailed technical explanation
How to think about this question
IPv6 hosts use Neighbor Discovery (ND) to resolve the link-layer address of a next-hop router. The host checks if the destination or default gateway is on-link by comparing the prefix length (here /64) with the destination address. Since the gateway is in a different /64 subnet, the host will not attempt ND for it and will not send packets to it, effectively treating the gateway as unreachable. This behavior is defined in RFC 4861 and is a common misconfiguration pitfall when statically assigning IPv6 addresses and gateways.
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 network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
What to study next
Got this wrong? Here's your next step.
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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: The PC's default gateway address is in a different subnet than the PC's IPv6 address. — The PC's IPv6 address is 2001:db8:acad:1::100/64, placing it in the 2001:db8:acad:1::/64 subnet. The configured default gateway is 2001:db8:acad:2::1, which belongs to the 2001:db8:acad:2::/64 subnet. For IPv6, a host will only consider a default gateway on the same link-local or on-link subnet; if the gateway address is not within the same /64 prefix as the host's address, the host cannot send packets to it directly, and all off-subnet traffic fails.
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.
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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.
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