- A
All neighbors are in a stable state.
Why wrong: The DELAY state indicates a transition; not all are stable.
- B
The neighbor 2001:DB8:1::3 is in DELAY state, meaning a Neighbor Solicitation will be sent soon.
DELAY state means a NS is pending after a delay timer.
- C
The neighbor 2001:DB8:1::2 is unreachable.
Why wrong: STALE state means the entry is valid but not recently verified.
- D
The link-local address FE80::1 is not valid.
Why wrong: It is REACH, so it is valid.
Question 1,835 of 2,152
300-410 IPv6 First Hop Security Practice Question
This 300-410 practice question tests your understanding of ipv6 first hop security. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 runs the following command on Router R1:
R1# show ipv6 neighbors
IPv6 Address Age Link-layer Addr State Interface 2001:DB8:1::1 0 aaaa.bbbb.cccc REACH Gi0/0/0 2001:DB8:1::2 10 aaaa.bbbb.cccd STALE Gi0/0/0 2001:DB8:1::3 - aaaa.bbbb.ccce DELAY Gi0/0/1 FE80::1 0 aaaa.bbbb.cccf REACH Gi0/0/0
Based on this output, which statement is correct?
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 neighbor 2001:DB8:1::3 is in DELAY state, meaning a Neighbor Solicitation will be sent soon.
Option B is correct because the DELAY state in IPv6 Neighbor Discovery (ND) indicates that a neighbor has not been confirmed reachable within the last 5 seconds, and the router will send a Neighbor Solicitation (NS) message after the DELAY timer expires (default 5 seconds) to verify reachability. The entry for 2001:DB8:1::3 shows a hyphen in the Age column, meaning it was just created or refreshed, and it is in DELAY, so an NS will be sent soon.
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.
- ✗
All neighbors are in a stable state.
Why it's wrong here
The DELAY state indicates a transition; not all are stable.
- ✓
The neighbor 2001:DB8:1::3 is in DELAY state, meaning a Neighbor Solicitation will be sent soon.
Why this is correct
DELAY state means a NS is pending after a delay timer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The neighbor 2001:DB8:1::2 is unreachable.
Why it's wrong here
STALE state means the entry is valid but not recently verified.
- ✗
The link-local address FE80::1 is not valid.
Why it's wrong here
It is REACH, so it is valid.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that STALE means unreachable or that DELAY is a failure state, when in fact STALE is a normal aging state and DELAY is a brief waiting period before probing.
Detailed technical explanation
How to think about this question
IPv6 Neighbor Discovery (RFC 4861) defines five reachability states: INCOMPLETE, REACHABLE, STALE, DELAY, and PROBE. The DELAY state is entered from STALE when a packet is sent to the neighbor, and the router waits up to 5 seconds for a reachability confirmation before transitioning to PROBE and sending unicast Neighbor Solicitations. In real-world scenarios, this mechanism prevents unnecessary NS flooding when a single packet is sent to a stale neighbor, such as during a brief network hiccup.
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 at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
What to study next
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FAQ
Questions learners often ask
What does this 300-410 question test?
IPv6 First Hop Security — This question tests IPv6 First Hop Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The neighbor 2001:DB8:1::3 is in DELAY state, meaning a Neighbor Solicitation will be sent soon. — Option B is correct because the DELAY state in IPv6 Neighbor Discovery (ND) indicates that a neighbor has not been confirmed reachable within the last 5 seconds, and the router will send a Neighbor Solicitation (NS) message after the DELAY timer expires (default 5 seconds) to verify reachability. The entry for 2001:DB8:1::3 shows a hyphen in the Age column, meaning it was just created or refreshed, and it is in DELAY, so an NS will be sent soon.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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