Question 592 of 2,152

IPv6 First Hop Security →hardMultiple ChoiceObjective-mapped

RA Guard Misconfiguration — device-role host on Router Port | Cisco CCNP ENARSI 300-410

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 is troubleshooting an IPv6 connectivity issue where hosts on VLAN 10 cannot reach the internet. The switch is configured with IPv6 First Hop Security features including RA Guard and DHCPv6 Guard. The legitimate router is connected to port Gi1/0/1. The engineer notices that the router is sending RAs, but hosts are not receiving them. The switch shows that RA Guard is dropping packets on port Gi1/0/1. What is the most likely misconfiguration?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "first"
Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
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.

A
The RA Guard policy is configured with 'device-role host' on port Gi1/0/1, which causes the switch to drop all RAs received on that port.
Correct because 'device-role host' tells the switch that only hosts are allowed on that port; RAs from a router will be dropped.
B
DHCPv6 Guard is configured on port Gi1/0/1, blocking the router's DHCPv6 server messages.
Why wrong: Incorrect because DHCPv6 Guard blocks DHCPv6 server messages, not RAs; the symptom is about RAs being dropped.
C
IPv6 Source Guard is enabled on the VLAN, and the router's IPv6 address is not in the binding table.
Why wrong: Incorrect because IPv6 Source Guard filters traffic based on source address, not RAs; RAs are multicast and typically not filtered by Source Guard.
D
The switch has IPv6 unicast-routing enabled, and it is sending its own RAs, causing a conflict.
Why wrong: Incorrect because the issue is that the router's RAs are being dropped, not that there are conflicting RAs.

Full breakdown with real-world context →

Quick Answer

The answer is that the RA Guard policy is misconfigured with device-role host on the router port Gi1/0/1. RA Guard is a First Hop Security feature that validates Router Advertisement messages; when a port is set to device-role host, the switch treats any device on that port as an end host and drops all incoming RAs, even from the legitimate router. This explains why the router sends RAs but hosts never receive them—the switch is actively blocking the advertisements at the port level. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of IPv6 RA Guard policy application and the critical distinction between device-role router and device-role host. A common trap is assuming RA Guard only blocks rogue devices, but misassigning the role on the trusted router port will also drop legitimate RAs. Remember the memory tip: “Host drops, Router allows”—if you want RAs to pass, the port facing the router must be configured with device-role router.

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 RA Guard policy is configured with 'device-role host' on port Gi1/0/1, which causes the switch to drop all RAs received on that port.

RA Guard drops Router Advertisements (RAs) on ports where the policy's 'device-role' is set to 'host'. On port Gi1/0/1, the legitimate router is connected, but if the RA Guard policy incorrectly assigns 'device-role host' to that port, the switch will treat the router as a host and drop all incoming RAs, preventing hosts on VLAN 10 from receiving them. This matches the symptom where the router sends RAs but hosts do not receive them, and the switch reports RA Guard dropping packets on that port.

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 RA Guard policy is configured with 'device-role host' on port Gi1/0/1, which causes the switch to drop all RAs received on that port.
Why this is correct
Correct because 'device-role host' tells the switch that only hosts are allowed on that port; RAs from a router will be dropped.
Clue confirmation
The clue words "first", "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
DHCPv6 Guard is configured on port Gi1/0/1, blocking the router's DHCPv6 server messages.
Why it's wrong here
Incorrect because DHCPv6 Guard blocks DHCPv6 server messages, not RAs; the symptom is about RAs being dropped.
✗
IPv6 Source Guard is enabled on the VLAN, and the router's IPv6 address is not in the binding table.
Why it's wrong here
Incorrect because IPv6 Source Guard filters traffic based on source address, not RAs; RAs are multicast and typically not filtered by Source Guard.
✗
The switch has IPv6 unicast-routing enabled, and it is sending its own RAs, causing a conflict.
Why it's wrong here
Incorrect because the issue is that the router's RAs are being dropped, not that there are conflicting RAs.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the specific behavior of RA Guard's 'device-role' setting, where candidates mistakenly think RA Guard only blocks RAs from unauthorized routers, but the trap is that setting 'device-role host' on a port will drop all RAs, including those from the legitimate router, because the switch treats that port as a host port.

Detailed technical explanation

How to think about this question

RA Guard, defined in RFC 6105, inspects incoming RAs and drops them if the port is not trusted (i.e., device-role is 'router' for trusted ports). The 'device-role host' setting on a port tells the switch to drop any RAs received on that port, as hosts should never send RAs. In real-world scenarios, this misconfiguration often occurs when an engineer applies a default RA Guard policy that assumes all ports are host-facing, forgetting to change the role on the uplink port connecting the legitimate router.

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 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.

Visual reference

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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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 RA Guard policy is configured with 'device-role host' on port Gi1/0/1, which causes the switch to drop all RAs received on that port. — RA Guard drops Router Advertisements (RAs) on ports where the policy's 'device-role' is set to 'host'. On port Gi1/0/1, the legitimate router is connected, but if the RA Guard policy incorrectly assigns 'device-role host' to that port, the switch will treat the router as a host and drop all incoming RAs, preventing hosts on VLAN 10 from receiving them. This matches the symptom where the router sends RAs but hosts do not receive them, and the switch reports RA Guard dropping packets on that port.

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.

Are there clue words in this question I should notice?

Yes — watch for: "first", "most likely". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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