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Question 554 of 1,052
hardmultiple choiceObjective-mapped
CCNA Practice Question: A network administrator is troubleshooting an…
This 200-301 practice question tests your understanding of 200-301 exam topics. 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.
Exhibit
Router# show ipv6 interface g0/0/0
GigabitEthernet0/0/0 is up, line protocol is up
IPv6 is enabled, link-local address is FE80::21A:2BFF:FE3C:4D5E
No global unicast address is configured
Joined group address(es):
FF02::1
FF02::2
FF02::1:FF3C:4D5E
MTU is 1500 bytes
ICMP error messages limited to one every 100 milliseconds
ICMP redirects are enabled
ICMP unreachables are sent
ND DAD is enabled, number of DAD attempts: 1
ND reachable time is 30000 milliseconds (using 30000)
ND advertised reachable time is 0 (unspecified)
ND advertised retransmit interval is 0 (unspecified)
ND router advertisements are sent every 200 seconds
ND router advertisements live for 1800 seconds
ND advertised default router preference is Medium
Hosts use stateless autoconfiguration for addresses.A network administrator is troubleshooting an IPv6 connectivity issue on a newly deployed router. The router's G0/0/0 interface is configured with an IPv6 address using EUI-64, but hosts on that subnet cannot reach the router's link-local address. The administrator runs 'show ipv6 interface g0/0/0' and sees that the interface is up/up but the IPv6 address is not in the expected format. What is the most likely cause of the problem?
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 IPv6 address was not configured correctly; the 'ipv6 address' command was likely omitted or misconfigured.
The output shows a link-local address using EUI-64 format (FE80::21A:2BFF:FE3C:4D5E), but no global unicast address. The 'No global unicast address is configured' line indicates that the IPv6 address was not assigned correctly. Since the interface is up and the link-local address is present, the issue is not hardware. The most likely cause is that the 'ipv6 address' command was omitted or incorrectly configured, such as using 'ipv6 address autoconfig' without a global prefix or not specifying a global address with EUI-64.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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 interface is administratively down.
Why it's wrong here
The output clearly shows 'up, line protocol is up', so the interface is not administratively down.
- ✓
The IPv6 address was not configured correctly; the 'ipv6 address' command was likely omitted or misconfigured.
Why this is correct
The lack of a global unicast address despite EUI-64 being used for the link-local address suggests that the global address configuration is missing or incorrect. The correct command would be 'ipv6 address 2001:DB8::/64 eui-64' or similar.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
CIDR notation defines the prefix length.
- ✗
The MAC address of the interface is invalid, preventing EUI-64 from generating a proper address.
Why it's wrong here
The link-local address is correctly formed using EUI-64 (FE80::21A:2BFF:FE3C:4D5E), indicating the MAC address is valid and EUI-64 is functioning.
- ✗
The router is not sending Router Advertisements, so hosts cannot autoconfigure.
Why it's wrong here
The output shows 'ND router advertisements are sent every 200 seconds', so RA is enabled. The problem is about the router's own address, not host autoconfiguration.
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 IPv6 address was not configured correctly; the 'ipv6 address' command was likely omitted or misconfigured.Correct answer▾
Why this is correct
The lack of a global unicast address despite EUI-64 being used for the link-local address suggests that the global address configuration is missing or incorrect. The correct command would be 'ipv6 address 2001:DB8::/64 eui-64' or similar.
✗The interface is administratively down.Wrong answer — click to see why▾
Why this is wrong here
The interface status is up/up, ruling out this option.
✗The MAC address of the interface is invalid, preventing EUI-64 from generating a proper address.Wrong answer — click to see why▾
Why this is wrong here
The link-local address is properly generated, so the MAC address is not the issue.
✗The router is not sending Router Advertisements, so hosts cannot autoconfigure.Wrong answer — click to see why▾
Why this is wrong here
RA is enabled and being sent, so this is not the cause.
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: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Trap categories for this question
Command / output trap
The output clearly shows 'up, line protocol is up', so the interface is not administratively down.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
- CIDR notation defines the prefix length.
- Block size helps identify subnet boundaries.
- Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
- The required host count determines the smallest suitable subnet.
TExam Day Tips
- Write the block size before choosing the subnet.
- Check whether the question asks for hosts, subnets or a specific address range.
- Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 200-301 subnetting questions on CIDR, address ranges, and subnet selection.
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FAQ
Questions learners often ask
What does this 200-301 question test?
CIDR notation defines the prefix length.
What is the correct answer to this question?
The correct answer is: The IPv6 address was not configured correctly; the 'ipv6 address' command was likely omitted or misconfigured. — The output shows a link-local address using EUI-64 format (FE80::21A:2BFF:FE3C:4D5E), but no global unicast address. The 'No global unicast address is configured' line indicates that the IPv6 address was not assigned correctly. Since the interface is up and the link-local address is present, the issue is not hardware. The most likely cause is that the 'ipv6 address' command was omitted or incorrectly configured, such as using 'ipv6 address autoconfig' without a global prefix or not specifying a global address with EUI-64.
What should I do if I get this 200-301 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 200-301 subnetting questions on CIDR, address ranges, and subnet selection.
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?
CIDR notation defines the prefix length.
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