- A
The interface filters all incoming IPv6 traffic unless the source address is in the DHCP snooping binding table.
IPv6 Source Guard checks source IPv6 and MAC against the binding table; unmatched traffic is dropped.
- B
The interface allows all IPv6 traffic but logs violations.
Why wrong: IPv6 Source Guard drops traffic, not just logs.
- C
The interface only filters Neighbor Discovery messages.
Why wrong: It filters all IPv6 traffic, not just ND.
- D
The interface requires a static binding to be configured first.
Why wrong: It uses dynamic DHCP snooping bindings; static bindings are optional.
Question 39 of 2,152
IPv6 Verify Source — Immediate Effect on Traffic | Cisco CCNP ENARSI 300-410
This 300-410 practice question tests your understanding of ipv6 first hop security. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 configures IPv6 Source Guard on an interface:
interface GigabitEthernet0/3
ipv6 verify source
What is the immediate effect of this command?
Quick Answer
The immediate effect of the `ipv6 verify source` command on a Cisco interface is that it filters all incoming IPv6 traffic unless the source address is present in the DHCPv6 snooping binding table. This occurs because IPv6 Source Guard, when configured without any additional parameters, defaults to using the DHCPv6 snooping database as its sole source of trust, dropping any packet whose source IPv6 or MAC address does not match a valid binding entry. On the Cisco CCNP ENARSI 300-410 exam, this concept tests your understanding of first-hop security features and how they interact with DHCP snooping; a common trap is assuming the command also checks neighbor discovery (ND) cache entries, which it does not unless you add the `nd` keyword. To remember this, think of the command as a strict bouncer at a club: if your name isn’t on the DHCP guest list, you’re not getting in.
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 interface filters all incoming IPv6 traffic unless the source address is in the DHCP snooping binding table.
The 'ipv6 verify source' command enables IPv6 Source Guard, which filters incoming IPv6 traffic on the interface. It permits only packets whose source IPv6 address matches a binding in the DHCPv6 snooping binding table (or static IPv6 source guard entries). Traffic from unknown or mismatched sources is dropped, preventing spoofing attacks.
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.
- ✓
The interface filters all incoming IPv6 traffic unless the source address is in the DHCP snooping binding table.
Why this is correct
IPv6 Source Guard checks source IPv6 and MAC against the binding table; unmatched traffic is dropped.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The interface allows all IPv6 traffic but logs violations.
Why it's wrong here
IPv6 Source Guard drops traffic, not just logs.
- ✗
The interface only filters Neighbor Discovery messages.
Why it's wrong here
It filters all IPv6 traffic, not just ND.
- ✗
The interface requires a static binding to be configured first.
Why it's wrong here
It uses dynamic DHCP snooping bindings; static bindings are optional.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that 'ipv6 verify source' requires a preconfigured static binding, but the command works dynamically with DHCPv6 snooping, and the trap is that candidates overlook the DHCP snooping dependency.
Detailed technical explanation
How to think about this question
IPv6 Source Guard leverages the DHCPv6 snooping binding table (populated via 'ipv6 dhcp snooping') to validate source addresses. It operates similarly to IPv4 Source Guard, using a per-interface ACL that matches allowed source prefixes. In real-world deployments, this is critical for preventing rogue IPv6 addresses on access ports, especially in enterprise networks with stateless address autoconfiguration (SLAAC) where DHCPv6 may not be used, requiring static bindings or neighbor discovery snooping integration.
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: The interface filters all incoming IPv6 traffic unless the source address is in the DHCP snooping binding table. — The 'ipv6 verify source' command enables IPv6 Source Guard, which filters incoming IPv6 traffic on the interface. It permits only packets whose source IPv6 address matches a binding in the DHCPv6 snooping binding table (or static IPv6 source guard entries). Traffic from unknown or mismatched sources is dropped, preventing spoofing attacks.
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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