hardMultiple ChoiceObjective-mapped
300-410 Practice Question: Runs the following command to debug IPv6 traffic…
A network engineer runs the following command to debug IPv6 traffic filtering:
R1# debug ipv6 packet access-list FILTER detail
IPv6 packet debugging is on for access list FILTER (detail)
*Mar 1 00:01:23.456: IPv6: source 2001:DB8:2::1 (GigabitEthernet0/0) *Mar 1 00:01:23.456: dest 2001:DB8:3::1 (GigabitEthernet0/1) *Mar 1 00:01:23.456: traffic class 0, flowlabel 0, hlim 64, next header 6 (TCP) *Mar 1 00:01:23.456: denied by access-list FILTER
What does this output indicate?
⚠ Common exam trap
Cisco often tests the misconception that a packet is permitted by default if the destination is not explicitly listed in the access list, but the implicit deny at the end of every IPv6 access list means any unmatched packet is denied, and the debug output here explicitly shows a deny due to a match on the source address.
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 packet is denied because the source address 2001:DB8:2::1 matches the deny entry in the access list.
The debug output explicitly states 'denied by access-list FILTER', confirming that the packet was dropped due to a match against a deny entry in the named IPv6 access list. The source address 2001:DB8:2::1 is shown as the matching source, and since the debug includes 'detail', it provides the exact reason for denial. Access lists process entries sequentially, and the first match (permit or deny) determines the action; here, the source matched a deny 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 packet is denied because the source address 2001:DB8:2::1 matches the deny entry in the access list.
Why this is correct
Correct. The debug clearly states the packet is denied by the access list, which has a deny for that source prefix.
- ✗
The packet is permitted because it is a TCP packet.
Why it's wrong here
Incorrect. The debug shows it is denied regardless of protocol.
- ✗
The packet is denied because of uRPF check failure.
Why it's wrong here
Incorrect. The debug explicitly says 'denied by access-list FILTER', not uRPF.
- ✗
The packet is permitted because the destination is not in the access list.
Why it's wrong here
Incorrect. The access list filters based on source; the packet is denied.
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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.