The answer is that the `ipv6 nd suppress` command blocks all Router Advertisement traffic on the port, including RAs forwarded from other router ports. This occurs because the command is designed to treat the switch port as a host-facing port, which means the switch not only stops sending its own RAs but also suppresses any RAs that would normally be flooded or forwarded from other VLAN interfaces. On the Cisco CCNP ENARSI 300-410 exam, this is a classic trap that tests your understanding of how IPv6 neighbor discovery suppression interacts with Layer 2 forwarding behavior—many engineers mistakenly assume the command only prevents the switch from originating RAs, but it actually drops all RA traffic on that port. A common memory tip is to think of "suppress" as "silence all RA traffic on this port," not just "stop sending." Remember: if you suppress RAs on a port, no router—local or remote—can reach that segment with advertisements.
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.
An engineer configures 'ipv6 nd suppress' on a switch port to prevent the switch from sending Router Advertisements. However, after this configuration, hosts on that port cannot obtain IPv6 addresses via SLAAC, even though a router on another port is sending RAs. What is the most likely explanation?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The 'ipv6 nd suppress' command blocks all RA traffic on the port, including RAs forwarded from other ports.
The 'ipv6 nd suppress' command on a switch port prevents the switch from sending RAs, but it does not forward RAs from other routers. In fact, on some platforms, 'ipv6 nd suppress' also blocks the forwarding of RAs received on other ports to that port, because the switch treats the port as a host port. This is an edge case where the command is misunderstood: it suppresses all RA traffic on that port, both outgoing and incoming (forwarded). The hosts never receive the router's RAs.
Key principle: A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
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 'ipv6 nd suppress' command blocks all RA traffic on the port, including RAs forwarded from other ports.
Why this is correct
Suppress prevents any RA from being sent or forwarded on that port.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Access ports place end devices into a single VLAN.
✗
The router's RAs are being filtered by an ACL on the switch.
Common exam trap: an active trunk can still block the VLAN you need
A trunk being up does not prove every VLAN is crossing it. Check allowed VLAN lists, native VLAN mismatch, VLAN existence and access-port assignment.
Detailed technical explanation
How to think about this question
VLAN questions usually combine access-port and trunking clues. The key is to identify whether the issue is local to one switchport, caused by the trunk, or caused by the VLAN not existing where it needs to exist.
KKey Concepts to Remember
Access ports place end devices into a single VLAN.
Trunk ports carry multiple VLANs between switches.
Allowed VLAN lists decide which VLANs can cross a trunk.
Native VLAN mismatch can create confusing symptoms.
TExam Day Tips
→Use show vlan brief to verify access VLANs.
→Use show interfaces trunk to verify trunk state and allowed VLANs.
→Do not treat every same-VLAN issue as a routing problem.
Key takeaway
A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
Real-world example
How this comes up in practice
A help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 300-410 questions on switching, trunking, and access-port configuration.
IPv6 First Hop Security — This question tests IPv6 First Hop Security — Access ports place end devices into a single VLAN..
What is the correct answer to this question?
The correct answer is: The 'ipv6 nd suppress' command blocks all RA traffic on the port, including RAs forwarded from other ports. — The 'ipv6 nd suppress' command on a switch port prevents the switch from sending RAs, but it does not forward RAs from other routers. In fact, on some platforms, 'ipv6 nd suppress' also blocks the forwarding of RAs received on other ports to that port, because the switch treats the port as a host port. This is an edge case where the command is misunderstood: it suppresses all RA traffic on that port, both outgoing and incoming (forwarded). The hosts never receive the router's RAs.
What should I do if I get this 300-410 question wrong?
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 300-410 questions on switching, trunking, and access-port configuration.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Access ports place end devices into a single VLAN.
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