- A
ND inspection is allowing NS messages but blocking NA messages from fe80::2, likely due to a MAC address mismatch or policy violation.
The NA is blocked, which could be due to the source MAC not matching the TLLA or policy rules.
- B
ND inspection is blocking all NS and NA messages, indicating a misconfiguration.
Why wrong: The NS from fe80::1 is allowed, so not all messages are blocked.
- C
ND inspection is allowing all messages but logging them for analysis.
Why wrong: The NA is explicitly blocked, so not all are allowed.
- D
ND inspection is not configured; the debug output is from default ND behavior.
Why wrong: The debug references policy INSPECT, indicating ND inspection is configured.
Question 639 of 2,152
300-410 IPv6 First Hop Security Practice Question
This 300-410 practice question tests your understanding of ipv6 first hop security. 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 runs the following command to troubleshoot IPv6 ND inspection:
R1# debug ipv6 nd inspection *Mar 1 00:02:34.567: IPv6-ND-Inspection: R1, Fa0/0, NS from fe80::1 to ff02::1, target 2001:db8::1, options: SLLA 0011.2233.4455 *Mar 1 00:02:34.567: IPv6-ND-Inspection: R1, Fa0/0, NS from fe80::1 to ff02::1, target 2001:db8::1, SLLA 0011.2233.4455 is allowed by policy INSPECT *Mar 1 00:02:35.890: IPv6-ND-Inspection: R1, Fa0/0, NA from fe80::2 to fe80::1, target 2001:db8::2, options: TLLA 00aa.bbcc.ddee *Mar 1 00:02:35.890: IPv6-ND-Inspection: R1, Fa0/0, NA from fe80::2 to fe80::1, target 2001:db8::2, TLLA 00aa.bbcc.ddee is blocked by policy INSPECT
What does this output indicate?
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
✓
ND inspection is allowing NS messages but blocking NA messages from fe80::2, likely due to a MAC address mismatch or policy violation.
The debug output shows that the Neighbor Solicitation (NS) from fe80::1 is allowed by policy INSPECT, while the Neighbor Advertisement (NA) from fe80::2 is blocked by the same policy. This indicates that IPv6 ND inspection is selectively permitting NS messages but denying NA messages from fe80::2, likely due to a MAC address mismatch (the TLLA in the NA does not match the expected binding) or a policy violation, making option A correct.
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.
- ✓
ND inspection is allowing NS messages but blocking NA messages from fe80::2, likely due to a MAC address mismatch or policy violation.
Why this is correct
The NA is blocked, which could be due to the source MAC not matching the TLLA or policy rules.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
ND inspection is blocking all NS and NA messages, indicating a misconfiguration.
Why it's wrong here
The NS from fe80::1 is allowed, so not all messages are blocked.
- ✗
ND inspection is allowing all messages but logging them for analysis.
Why it's wrong here
The NA is explicitly blocked, so not all are allowed.
- ✗
ND inspection is not configured; the debug output is from default ND behavior.
Why it's wrong here
The debug references policy INSPECT, indicating ND inspection is configured.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between NS and NA handling in ND inspection, where candidates may assume both messages are treated identically, but the policy can allow one and block the other based on binding table validation.
Detailed technical explanation
How to think about this question
IPv6 ND inspection (RFC 4861) uses a binding table to validate Neighbor Discovery messages; a Neighbor Advertisement with a Target Link-Layer Address (TLLA) that does not match the binding table entry for the source IPv6 address is blocked to prevent spoofing. The debug output shows the NA from fe80::2 to fe80::1 with TLLA 00aa.bbcc.ddee is blocked, suggesting the binding table either lacks an entry for fe80::2 or the MAC address does not match, while the NS with SLLA 0011.2233.4455 is allowed because it matches the policy.
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.
Visual reference
Quick reference
Access Control Model Comparison
| Model | Acronym | Who Controls Access? | Best For |
|---|---|---|---|
| Discretionary Access Control | DAC | Resource owner | Small teams, file shares |
| Mandatory Access Control | MAC | System / security labels | Classified govt / military |
| Role-Based Access Control | RBAC | Administrator (via roles) | Enterprise environments |
| Attribute-Based Access Control | ABAC | Policy engine (user + resource attributes) | Fine-grained, dynamic policies |
| Rule-Based Access Control | RuBAC | System rules / ACLs | Firewall rules, network ACLs |
What to study next
Got this wrong? Here's your next step.
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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: ND inspection is allowing NS messages but blocking NA messages from fe80::2, likely due to a MAC address mismatch or policy violation. — The debug output shows that the Neighbor Solicitation (NS) from fe80::1 is allowed by policy INSPECT, while the Neighbor Advertisement (NA) from fe80::2 is blocked by the same policy. This indicates that IPv6 ND inspection is selectively permitting NS messages but denying NA messages from fe80::2, likely due to a MAC address mismatch (the TLLA in the NA does not match the expected binding) or a policy violation, making option A correct.
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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