- A
The interface is in a down state due to a Layer 1 issue, preventing RA generation.
Why wrong: No interface down indication is given; the issue is configuration-based.
- B
The 'ipv6 nd suppress-ra' command is configured, which prevents Router Advertisements from being sent.
This command suppresses all RAs, so hosts cannot autoconfigure or learn the default router.
- C
Router R2 has IPv6 routing disabled, so it cannot process RAs from R1.
Why wrong: R2's neighbor cache would still show R1's link-local address if RAs were received.
- D
The IPv6 address on R1 is not in the same subnet as the hosts, causing RA filtering.
Why wrong: The address is in the same subnet; RA filtering is not standard behavior.
Question 1,388 of 2,152
IPv6 Router Advertisement Suppression: ipv6 nd suppress-ra Issue
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 notices that IPv6 hosts on a segment are not receiving Router Advertisements, even though Router R1 has IPv6 unicast-routing enabled and an IPv6 address on the interface. Router R1 has the following relevant configuration:
interface GigabitEthernet0/0
ipv6 address 2001:DB8:1::1/64 ipv6 nd suppress-ra !
Router R2, connected to the same segment, shows: no IPv6 neighbors in the neighbor cache for R1's link-local address. What is the root cause?
Quick Answer
The answer is the ipv6 nd suppress-ra command, which is the root cause of the Router Advertisement suppression misconfiguration. This command explicitly prevents the router from sending Router Advertisements (RAs) on the interface, so even though IPv6 unicast-routing is enabled and an address is configured, hosts never receive the RAs needed to learn the prefix, default gateway, and autoconfiguration parameters. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of IPv6 neighbor discovery operations and the distinction between address assignment via DHCPv6 and the mandatory RA process for default route discovery. A common trap is assuming that enabling IPv6 routing alone is sufficient for RA generation, or that DHCPv6 eliminates the need for RAs—it does not, as hosts still require RAs for default gateway detection. Memory tip: think of suppress-ra as "silencing the RA," so if hosts are missing their default route, check for this command first.
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 'ipv6 nd suppress-ra' command is configured, which prevents Router Advertisements from being sent.
The 'ipv6 nd suppress-ra' command explicitly disables the sending of Router Advertisements (RAs) on the interface. Even though IPv6 unicast-routing is enabled and an IPv6 address is configured, R1 will not transmit RAs, which prevents IPv6 hosts from autoconfiguring their addresses and default routes via SLAAC or DHCPv6. This is the direct root cause of the hosts not receiving RAs.
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 is in a down state due to a Layer 1 issue, preventing RA generation.
Why it's wrong here
No interface down indication is given; the issue is configuration-based.
- ✓
The 'ipv6 nd suppress-ra' command is configured, which prevents Router Advertisements from being sent.
Why this is correct
This command suppresses all RAs, so hosts cannot autoconfigure or learn the default router.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Router R2 has IPv6 routing disabled, so it cannot process RAs from R1.
Why it's wrong here
R2's neighbor cache would still show R1's link-local address if RAs were received.
- ✗
The IPv6 address on R1 is not in the same subnet as the hosts, causing RA filtering.
Why it's wrong here
The address is in the same subnet; RA filtering is not standard behavior.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the 'ipv6 nd suppress-ra' command as a direct countermeasure to RA generation, and the trap here is that candidates assume IPv6 unicast-routing alone is sufficient for RA generation, overlooking the explicit suppression command.
Trap categories for this question
Command / output trap
R2's neighbor cache would still show R1's link-local address if RAs were received.
Detailed technical explanation
How to think about this question
Router Advertisements are sent periodically and in response to Router Solicitations as defined in RFC 4861. The 'ipv6 nd suppress-ra' command is often used on interfaces where you want to prevent hosts from autoconfiguring, such as on point-to-point links or when using static addressing exclusively. A subtle behavior is that even with suppress-ra enabled, the router still responds to Neighbor Solicitations for its own address, but it will not send unsolicited RAs or respond to Router Solicitations.
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
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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 'ipv6 nd suppress-ra' command is configured, which prevents Router Advertisements from being sent. — The 'ipv6 nd suppress-ra' command explicitly disables the sending of Router Advertisements (RAs) on the interface. Even though IPv6 unicast-routing is enabled and an IPv6 address is configured, R1 will not transmit RAs, which prevents IPv6 hosts from autoconfiguring their addresses and default routes via SLAAC or DHCPv6. This is the direct root cause of the hosts not receiving RAs.
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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