mediumMultiple ChoiceObjective-mapped
300-410 Practice Question: Is troubleshooting a connectivity issue between…
A network engineer is troubleshooting a connectivity issue between two routers R1 and R2 connected via GigabitEthernet0/0. The engineer notices that R1 can ping its own IPv6 address 2001:db8:1::1/64, but cannot ping R2's interface address 2001:db8:1::2/64. The output of 'show ipv6 interface GigabitEthernet0/0' on R1 indicates that IPv6 is enabled and the interface is up/up. The engineer checks the access list applied to the interface and sees an inbound IPv6 ACL that permits only ICMPv6 echo requests from a specific source. What is the most likely cause of the ping failure?
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 ACL is applied inbound on R1 and does not permit ICMPv6 echo replies from R2.
The inbound ACL on R1 is blocking the ICMPv6 echo reply from R2, because the ACL only permits echo requests from a specific source, not replies. For a successful ping, both the echo request and echo reply must be permitted. The reply is sourced from R2's address, which is not matched by the permit statement.
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 ACL is applied inbound on R1 and does not permit ICMPv6 echo replies from R2.
Why this is correct
Correct because ICMPv6 echo replies are sourced from the destination address (R2) and must be permitted inbound on R1 for the ping to succeed.
- ✗
The ACL is applied outbound on R1 and blocks the echo request.
Why it's wrong here
Incorrect because the ACL is applied inbound, not outbound.
- ✗
IPv6 unicast-routing is not enabled on R1.
Why it's wrong here
Incorrect because R1 can ping its own address, indicating IPv6 is operational; unicast-routing is not required for direct link pings.
- ✗
The ACL is missing a permit statement for IPv6 neighbor discovery (ND) messages.
Why it's wrong here
Incorrect because ND messages are needed for address resolution, but the symptom is a ping failure after ND has likely succeeded (R1 can ping its own address, implying layer 2 is up).
Visual reference
Go deeper
Related to this question
About these practice questions
One of 1,966 original 300-410 practice questions on Courseiva, each with a full explanation and wrong-answer analysis — not exam dumps or protected exam content. Learn why practice questions differ from exam dumps →
JA
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.