Question 787 of 2,152

IPv6 First Hop Security →mediumMultiple ChoiceObjective-mapped

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.

A network engineer is troubleshooting an issue where IPv6 hosts are receiving multiple Router Advertisements from different routers, causing routing instability. The switch is configured with IPv6 First Hop Security features. The engineer wants to ensure that only the primary router's RAs are accepted by hosts. What is the most effective solution?

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: "primary"
Why it matters: Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.

A
Configure RA Guard with a policy that includes the primary router's MAC address in the allowed list and apply it to all ports.
Correct because RA Guard will drop RAs from any router not in the allowed list, preventing multiple routers from sending RAs.
B
Enable DHCPv6 Guard to block DHCPv6 messages from the secondary router.
Why wrong: Incorrect because DHCPv6 Guard does not affect RAs; it only blocks DHCPv6 server messages.
C
Use IPv6 Source Guard to filter traffic from the secondary router.
Why wrong: Incorrect because IPv6 Source Guard filters data traffic, not RAs.
D
Configure the switch to act as a router and send its own RAs with a higher priority to override the secondary router.
Why wrong: Incorrect because this would add another router sending RAs, potentially worsening the instability; RA Guard is the correct tool.

Full breakdown with real-world context →

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 includes the primary router's MAC address in the allowed list and apply it to all ports.

RA Guard with a policy that includes the primary router's MAC address in the allowed list is the most effective solution because it filters Router Advertisements (RAs) at Layer 2, permitting only RAs from the trusted primary router. This directly addresses the issue of multiple RAs causing routing instability by blocking RAs from any other source, such as the secondary router, without affecting other IPv6 traffic. RA Guard is an IPv6 First Hop Security feature designed specifically to prevent rogue or unwanted RAs from being processed by hosts.

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 includes the primary router's MAC address in the allowed list and apply it to all ports.
Why this is correct
Correct because RA Guard will drop RAs from any router not in the allowed list, preventing multiple routers from sending RAs.
Clue confirmation
The clue words "first", "primary" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Enable DHCPv6 Guard to block DHCPv6 messages from the secondary router.
Why it's wrong here
Incorrect because DHCPv6 Guard does not affect RAs; it only blocks DHCPv6 server messages.
✗
Use IPv6 Source Guard to filter traffic from the secondary router.
Why it's wrong here
Incorrect because IPv6 Source Guard filters data traffic, not RAs.
✗
Configure the switch to act as a router and send its own RAs with a higher priority to override the secondary router.
Why it's wrong here
Incorrect because this would add another router sending RAs, potentially worsening the instability; RA Guard is the correct tool.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the distinction between IPv6 First Hop Security features, where candidates confuse RA Guard (which filters RAs) with DHCPv6 Guard (which filters DHCPv6 messages) or IPv6 Source Guard (which prevents address spoofing), leading them to select an option that addresses a different type of attack or instability.

Detailed technical explanation

How to think about this question

RA Guard operates by inspecting ICMPv6 Type 134 (Router Advertisement) messages and applying a policy that can permit or deny based on source MAC address, prefix, or other criteria, as defined in RFC 6105. When applied to switch ports, it drops RAs from unauthorized sources at the hardware level before they reach hosts, ensuring only the primary router's RAs are forwarded. In a real-world scenario, this is critical in networks with redundant routers where a secondary router might be misconfigured or compromised, causing hosts to switch default gateways unpredictably.

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 security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.

Quick reference

Access Control Model Comparison

Model	Acronym	Who Controls Access?	Best For
Discretionary Access Control	DAC	Resource owner	Small teams, file shares
Mandatory Access Control	MAC	System / security labels	Classified govt / military
Role-Based Access Control	RBAC	Administrator (via roles)	Enterprise environments
Attribute-Based Access Control	ABAC	Policy engine (user + resource attributes)	Fine-grained, dynamic policies
Rule-Based Access Control	RuBAC	System rules / ACLs	Firewall rules, network ACLs

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 includes the primary router's MAC address in the allowed list and apply it to all ports. — RA Guard with a policy that includes the primary router's MAC address in the allowed list is the most effective solution because it filters Router Advertisements (RAs) at Layer 2, permitting only RAs from the trusted primary router. This directly addresses the issue of multiple RAs causing routing instability by blocking RAs from any other source, such as the secondary router, without affecting other IPv6 traffic. RA Guard is an IPv6 First Hop Security feature designed specifically to prevent rogue or unwanted RAs from being processed by hosts.

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", "primary". 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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