Question 373 of 2,152

IPv6 First Hop Security →hardMultiple ChoiceObjective-mapped

RA Guard Rogue Router Advertisement Prevention: Configuration Guide

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 issue where a rogue IPv6 router is sending false Router Advertisements on the network, causing hosts to use a malicious default gateway. The switch is configured with IPv6 First Hop Security features. The engineer wants to prevent this attack while allowing the legitimate router to send RAs. What is the correct configuration approach?

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.

A
Configure RA Guard with a policy that sets the legitimate router's port as 'device-role router' and all other ports as 'device-role host', and apply the policy globally.
Correct because RA Guard will allow RAs only on ports configured as 'device-role router', blocking rogue RAs on host ports.
B
Enable DHCPv6 Guard on all ports to block any DHCPv6 server messages, which will also block RAs.
Why wrong: Incorrect because DHCPv6 Guard does not block RAs; it only blocks DHCPv6 server messages.
C
Use IPv6 Source Guard to filter traffic from the rogue router based on its IPv6 address.
Why wrong: Incorrect because IPv6 Source Guard filters data traffic, not control plane messages like RAs; RA Guard is the appropriate feature.
D
Configure a static IPv6 neighbor entry for the legitimate router on the switch to override rogue RAs.
Why wrong: Incorrect because static neighbor entries do not prevent the switch from processing rogue RAs; RA Guard is needed to drop them.

Full breakdown with real-world context →

Quick Answer

The correct configuration approach is to configure RA Guard with a policy that sets the legitimate router’s port as device-role router and all other ports as device-role host, then apply the policy globally. This works because RA Guard is an IPv6 First Hop Security feature that inspects incoming Router Advertisements and drops any RA received on a port not explicitly trusted as a router port, thereby preventing rogue router advertisement prevention while allowing the authorized router to send legitimate RAs. On the Cisco CCNP ENARSI 300-410 exam, this topic tests your understanding of IPv6 RA Guard configuration under the First Hop Security domain, often appearing in scenario-based questions where a malicious RA attack must be mitigated without disrupting legitimate traffic. A common trap is applying the policy per-interface instead of globally, or forgetting to set the device-role on the trusted port. Memory tip: think “trust the port, guard the rest”—only the port with device-role router is allowed to send RAs.

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

✓

Configure RA Guard with a policy that sets the legitimate router's port as 'device-role router' and all other ports as 'device-role host', and apply the policy globally.

RA Guard is the correct IPv6 First Hop Security feature to block rogue Router Advertisements (RAs) while allowing legitimate RAs. By configuring a policy that sets the legitimate router's port as 'device-role router' and all other ports as 'device-role host', the switch will forward RAs only from the trusted router port and drop RAs received on host ports. This directly prevents the attack described.

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.

✓
Configure RA Guard with a policy that sets the legitimate router's port as 'device-role router' and all other ports as 'device-role host', and apply the policy globally.
Why this is correct
Correct because RA Guard will allow RAs only on ports configured as 'device-role router', blocking rogue RAs on host ports.
Clue confirmation
The clue word "first" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Enable DHCPv6 Guard on all ports to block any DHCPv6 server messages, which will also block RAs.
Why it's wrong here
Incorrect because DHCPv6 Guard does not block RAs; it only blocks DHCPv6 server messages.
✗
Use IPv6 Source Guard to filter traffic from the rogue router based on its IPv6 address.
Why it's wrong here
Incorrect because IPv6 Source Guard filters data traffic, not control plane messages like RAs; RA Guard is the appropriate feature.
✗
Configure a static IPv6 neighbor entry for the legitimate router on the switch to override rogue RAs.
Why it's wrong here
Incorrect because static neighbor entries do not prevent the switch from processing rogue RAs; RA Guard is needed to drop them.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the distinction between IPv6 First Hop Security features (RA Guard, DHCPv6 Guard, Source Guard, ND Inspection) and expects candidates to know that only RA Guard specifically blocks rogue Router Advertisements based on port role.

Detailed technical explanation

How to think about this question

RA Guard uses the IPv6 Router Advertisement Guard (RFC 6105) to inspect incoming RAs and enforce a policy based on the port's device role. The switch examines the source MAC address and the ICMPv6 type (134) to identify RAs; if a host port sends an RA, it is dropped. In a real-world scenario, a misconfigured host or an attacker could send RAs with a low hop limit to override a legitimate router, and RA Guard with device-role host prevents this without requiring per-host ACLs.

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.

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: Configure RA Guard with a policy that sets the legitimate router's port as 'device-role router' and all other ports as 'device-role host', and apply the policy globally. — RA Guard is the correct IPv6 First Hop Security feature to block rogue Router Advertisements (RAs) while allowing legitimate RAs. By configuring a policy that sets the legitimate router's port as 'device-role router' and all other ports as 'device-role host', the switch will forward RAs only from the trusted router port and drop RAs received on host ports. This directly prevents the attack described.

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". 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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