hardMultiple ChoiceObjective-mapped
300-410 Practice Question: Notices that IPv6 hosts on a segment are not…
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?
⚠ Common exam trap
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.
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.
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.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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