- A
Only Gi0/0/0 and Gi0/0/1 have source guard enabled.
Why wrong: Gi0/0/2 also has source guard via the default policy.
- B
Source guard is enabled on all interfaces, preventing IPv6 address spoofing.
All interfaces show active state with source guard policy.
- C
Source guard is disabled on Gi0/0/2 because it uses the default policy.
Why wrong: Default policy still enables source guard with role 'host'.
- D
Role 'host' means the interface is a router port.
Why wrong: Role 'host' indicates it is a host-facing port.
Question 203 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 source-guard policy Interface Policy Role State
Gi0/0/0 SRC_GUARD host ACTIVE Gi0/0/1 SRC_GUARD host ACTIVE Gi0/0/2 (default) host ACTIVE
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
✓
Source guard is enabled on all interfaces, preventing IPv6 address spoofing.
The output shows that Gi0/0/2 uses the (default) policy, which still applies IPv6 source guard with the role 'host' and state 'ACTIVE'. This means source guard is enabled on all three interfaces, preventing IPv6 address spoofing by filtering traffic based on the source address learned via Neighbor Discovery (ND) or DHCPv6.
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.
- ✗
Only Gi0/0/0 and Gi0/0/1 have source guard enabled.
Why it's wrong here
Gi0/0/2 also has source guard via the default policy.
- ✓
Source guard is enabled on all interfaces, preventing IPv6 address spoofing.
Why this is correct
All interfaces show active state with source guard policy.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Source guard is disabled on Gi0/0/2 because it uses the default policy.
Why it's wrong here
Default policy still enables source guard with role 'host'.
- ✗
Role 'host' means the interface is a router port.
Why it's wrong here
Role 'host' indicates it is a host-facing port.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume 'default' policy means disabled or no protection, but in IPv6 source guard, the default policy still enforces source guard filtering with the host role.
Detailed technical explanation
How to think about this question
IPv6 source guard uses the binding table (populated by ND snooping or DHCPv6 snooping) to validate the source IPv6 address of packets received on a port. On a host port, only the learned source address is allowed; any other source address is dropped. The default policy applies the same filtering logic as a custom policy, so Gi0/0/2 is still protected against spoofing even without an explicit policy name.
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
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: Source guard is enabled on all interfaces, preventing IPv6 address spoofing. — The output shows that Gi0/0/2 uses the (default) policy, which still applies IPv6 source guard with the role 'host' and state 'ACTIVE'. This means source guard is enabled on all three interfaces, preventing IPv6 address spoofing by filtering traffic based on the source address learned via Neighbor Discovery (ND) or DHCPv6.
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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