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.
300-410 IPv6 First Hop Security Practice Question
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:
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 suppresses Router Advertisements, which prevents hosts from learning the prefix and default route. This is a common misconfiguration when an administrator intends to use DHCPv6 for address assignment but forgets that hosts still need RAs for default gateway discovery. The correct answer identifies this suppression as the root cause.
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
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.
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: OSPF can fail even when IP connectivity looks correct
OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.
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
OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.
KKey Concepts to Remember
OSPF neighbours must agree on key parameters.
Router ID selection can affect neighbour relationships and LSDB output.
OSPF cost influences the preferred path.
A route can appear in OSPF information but not become the installed route.
TExam Day Tips
→Check area mismatch first when OSPF adjacency fails.
→Review passive interfaces when a network is advertised but no neighbour forms.
→Use show ip ospf neighbor and show ip route clues carefully.
Key takeaway
OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
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.
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 OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 300-410 OSPF questions on adjacency and route selection.
IPv6 First Hop Security — This question tests IPv6 First Hop Security — OSPF neighbours must agree on key parameters..
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 suppresses Router Advertisements, which prevents hosts from learning the prefix and default route. This is a common misconfiguration when an administrator intends to use DHCPv6 for address assignment but forgets that hosts still need RAs for default gateway discovery. The correct answer identifies this suppression as the root cause.
What should I do if I get this 300-410 question wrong?
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 300-410 OSPF questions on adjacency and route selection.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
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