- A
The access list will permit traffic from 2001:DB8:1::/48 and deny traffic from 2001:DB8:2::/48, but permit all other IPv6 traffic.
Correct. Sequence 10 permits the first prefix, sequence 20 denies the second, and sequence 30 permits everything else.
- B
The access list will permit traffic from 2001:DB8:1::/48 and deny traffic from 2001:DB8:2::/48, and implicitly deny all other IPv6 traffic.
Why wrong: Incorrect. There is an explicit permit any any at sequence 30, so other traffic is permitted.
- C
The access list will deny all traffic because of the deny statement.
Why wrong: Incorrect. The deny only applies to the specified prefix; other traffic is permitted by sequence 30.
- D
The access list is invalid because IPv6 access lists require implicit deny at the end.
Why wrong: Incorrect. IPv6 access lists do have an implicit deny, but the explicit permit any any overrides it.
300-410 IPv6 Traffic Filtering and uRPF Practice Question
This 300-410 practice question tests your understanding of ipv6 traffic filtering and urpf. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 runs the following command to troubleshoot an IPv6 traffic filtering issue:
R1# show ipv6 access-list FILTER
IPv6 access list FILTER
permit ipv6 2001:DB8:1::/48 any sequence 10
deny ipv6 2001:DB8:2::/48 any sequence20
permit ipv6 any any sequence 30
What does this output indicate?
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 access list will permit traffic from 2001:DB8:1::/48 and deny traffic from 2001:DB8:2::/48, but permit all other IPv6 traffic.
The output shows an IPv6 access list with three explicit entries. Sequence 10 permits traffic from source 2001:DB8:1::/48 to any destination, sequence 20 denies traffic from 2001:DB8:2::/48 to any destination, and sequence 30 permits all other IPv6 traffic. Because sequence 30 explicitly permits any any, traffic not matching the first two entries is permitted, overriding the default implicit deny at the end of the list.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 access list will permit traffic from 2001:DB8:1::/48 and deny traffic from 2001:DB8:2::/48, but permit all other IPv6 traffic.
Why this is correct
Correct. Sequence 10 permits the first prefix, sequence 20 denies the second, and sequence 30 permits everything else.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The access list will permit traffic from 2001:DB8:1::/48 and deny traffic from 2001:DB8:2::/48, and implicitly deny all other IPv6 traffic.
Why it's wrong here
Incorrect. There is an explicit permit any any at sequence 30, so other traffic is permitted.
- ✗
The access list will deny all traffic because of the deny statement.
Why it's wrong here
Incorrect. The deny only applies to the specified prefix; other traffic is permitted by sequence 30.
- ✗
The access list is invalid because IPv6 access lists require implicit deny at the end.
Why it's wrong here
Incorrect. IPv6 access lists do have an implicit deny, but the explicit permit any any overrides it.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the interaction between explicit permit entries and the implicit deny, where candidates mistakenly assume the implicit deny applies even when a later explicit permit any any exists.
Detailed technical explanation
How to think about this question
IPv6 access lists are processed top-down by sequence number, and the first matching entry is applied. The implicit deny any any at the end is a standard behavior for both IPv4 and IPv6 access lists (per RFC 2460 and Cisco implementation). In real-world scenarios, forgetting to add a permit any any entry after deny statements can cause unintended traffic drops, but here the explicit permit ensures all non-denied traffic is allowed.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
Visual reference
What to study next
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FAQ
Questions learners often ask
What does this 300-410 question test?
IPv6 Traffic Filtering and uRPF — This question tests IPv6 Traffic Filtering and uRPF — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The access list will permit traffic from 2001:DB8:1::/48 and deny traffic from 2001:DB8:2::/48, but permit all other IPv6 traffic. — The output shows an IPv6 access list with three explicit entries. Sequence 10 permits traffic from source 2001:DB8:1::/48 to any destination, sequence 20 denies traffic from 2001:DB8:2::/48 to any destination, and sequence 30 permits all other IPv6 traffic. Because sequence 30 explicitly permits any any, traffic not matching the first two entries is permitted, overriding the default implicit deny at the end of the list.
What should I do if I get this 300-410 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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