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 source guard:
R1# debug ipv6 source-guard
*Mar 1 00:04:56.789: IPv6-Source-Guard: R1, Fa0/0, IPv6 packet from 2001:db8::5, src MAC 0011.2233.4455, dst 2001:db8::1
*Mar 1 00:04:56.789: IPv6-Source-Guard: R1, Fa0/0, Binding lookup: 2001:db8::5 not found in binding table
*Mar 1 00:04:56.789: IPv6-Source-Guard: R1, Fa0/0, Packet dropped: source 2001:db8::5 not allowed
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
IPv6 source guard is dropping packets from sources not in the binding table, preventing spoofing.
The debug shows IPv6 source guard dropping a packet because the source address 2001:db8::5 is not in the binding table, indicating an unauthorized source.
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.
✓
IPv6 source guard is dropping packets from sources not in the binding table, preventing spoofing.
Why this is correct
The packet is dropped because the source address is not found in the binding table.
Related concept
Read the scenario before looking for a memorised answer.
✗
IPv6 source guard is allowing the packet because the source MAC matches.
Why it's wrong here
The packet is dropped, not allowed.
✗
IPv6 source guard is not configured; the debug output is from default IPv6 forwarding.
Why it's wrong here
The debug references source guard, indicating it is configured.
✗
IPv6 source guard is learning the binding from the packet and will allow future packets.
Why it's wrong here
The packet is dropped, and there is no indication of learning.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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 practitioner preparing for the 300-410 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
Identify which 300-410 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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: IPv6 source guard is dropping packets from sources not in the binding table, preventing spoofing. — The debug shows IPv6 source guard dropping a packet because the source address 2001:db8::5 is not in the binding table, indicating an unauthorized source.
What should I do if I get this 300-410 question wrong?
Identify which 300-410 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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