hardMultiple ChoiceObjective-mapped
300-410 Practice Question: Is troubleshooting IPv6 connectivity issues on a…
A network engineer is troubleshooting IPv6 connectivity issues on a multi-access segment where Router R1 and Router R2 are both acting as default routers. Hosts on the segment are not using R1 as a preferred router, even though R1 has a higher router preference. Router R1 has the following relevant configuration:
interface GigabitEthernet0/0
ipv6 address 2001:DB8:1::1/64 ipv6 nd router-preference high !
Router R2 shows: debug ipv6 nd output indicates that R2 is sending RAs with default preference (medium). What is the root cause?
⚠ Common exam trap
Cisco often tests the misconception that router preference alone guarantees selection, but the trap here is that an ACL or other filter can silently drop RAs, making the preference irrelevant because hosts never receive the RA.
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
✓
An IPv6 ACL applied to the interface is blocking Router Advertisements from R1.
An IPv6 ACL applied to the interface can filter Router Advertisement (RA) messages. If R1's RAs are blocked, hosts will never receive the high-preference indication and will instead use R2's default-preference RAs, causing R1 not to be preferred. The debug output confirms R2 is sending RAs with medium preference, and R1's configuration explicitly sets preference high, so the only explanation for hosts ignoring R1's preference is that its RAs are not reaching them.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Router R1's RA interval is set too high, causing hosts to prefer R2's more frequent RAs.
Why it's wrong here
The RA interval is not shown; preference should override frequency per RFC.
- ✓
An IPv6 ACL applied to the interface is blocking Router Advertisements from R1.
Why this is correct
An ACL with an implicit deny can block RAs, even if the router is configured to send them with high preference.
- ✗
Router R2 is configured with 'ipv6 nd router-preference high' as well, overriding R1's preference.
Why it's wrong here
The debug shows R2 sends medium preference, not high.
- ✗
Hosts are configured to ignore router preference due to a security policy.
Why it's wrong here
Hosts typically follow RFC 4191 unless explicitly configured otherwise.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.