300-410 IPv6 Traffic Filtering and uRPF Practice Question
This 300-410 practice question tests your understanding of ipv6 traffic filtering and urpf. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 on Router R1:
R1# show ipv6 access-list DENY-REMOTE
IPv6 access list DENY-REMOTE
deny ipv6 2001:DB8:2::/48 any sequence 10
permit ipv6 any any sequence 20
Based on this output, what is the effect of this access list when applied to an interface?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
It denies all IPv6 traffic from 2001:DB8:2::/48 and permits everything else
The access list DENY-REMOTE explicitly denies IPv6 traffic sourced from the prefix 2001:DB8:2::/48 (sequence 10) and then permits all other IPv6 traffic (sequence 20). When applied to an interface, this results in only traffic from that specific prefix being blocked, while all other IPv6 traffic is allowed. This matches option B.
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.
✗
It permits all IPv6 traffic
Why it's wrong here
Traffic from the specified prefix is denied.
✓
It denies all IPv6 traffic from 2001:DB8:2::/48 and permits everything else
Why this is correct
Sequence 10 denies the prefix, sequence 20 permits all other traffic.
Related concept
Read the scenario before looking for a memorised answer.
✗
It permits only IPv6 traffic from 2001:DB8:2::/48
Why it's wrong here
The ACL does the opposite – it denies that prefix.
✗
It denies all IPv6 traffic
Why it's wrong here
Only traffic from the specified prefix is denied; other traffic is permitted.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the concept that an ACL with an explicit permit any any at the end overrides the implicit deny, so candidates mistakenly think the ACL only denies or only permits based on the first line, ignoring the sequence of entries.
Detailed technical explanation
How to think about this question
IPv6 access lists operate similarly to IPv4 extended ACLs, using a first-match logic where the first matching entry determines the action. The 'any' keyword in the source or destination fields matches all IPv6 addresses, and the implicit deny at the end of the ACL would block all other traffic if no permit entry existed; here, the explicit permit any any ensures all non-denied traffic is allowed. In real-world scenarios, such ACLs are often applied inbound on WAN interfaces to block specific remote site prefixes while allowing all other IPv6 traffic.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
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: It denies all IPv6 traffic from 2001:DB8:2::/48 and permits everything else — The access list DENY-REMOTE explicitly denies IPv6 traffic sourced from the prefix 2001:DB8:2::/48 (sequence 10) and then permits all other IPv6 traffic (sequence 20). When applied to an interface, this results in only traffic from that specific prefix being blocked, while all other IPv6 traffic is allowed. This matches option B.
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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Question Discussion
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