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 PERMIT-ONLY
IPv6 access list PERMIT-ONLY
permit ipv6 2001:DB8:3::/48 any sequence 10
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 permits only IPv6 traffic from 2001:DB8:3::/48 and denies everything else
Option B is correct because an IPv6 access list, like its IPv4 counterpart, has an implicit deny all at the end. The single permit entry for source 2001:DB8:3::/48 allows only traffic from that prefix; all other IPv6 traffic is denied by the implicit deny ipv6 any any rule.
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
Only traffic from the specified prefix is permitted; other traffic is implicitly denied.
✓
It permits only IPv6 traffic from 2001:DB8:3::/48 and denies everything else
Why this is correct
The permit statement allows the prefix, and the implicit deny denies all other traffic.
Related concept
Read the scenario before looking for a memorised answer.
It permits all IPv6 traffic except from 2001:DB8:3::/48
Why it's wrong here
The ACL does the opposite – it permits that prefix and denies all else.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the implicit deny any any behavior in IPv6 ACLs, tricking candidates into thinking that a single permit entry allows all traffic or that the ACL only filters the specified prefix without affecting other traffic.
Detailed technical explanation
How to think about this question
IPv6 access lists use the same implicit deny any any logic as IPv4 ACLs, but they are applied with the ipv6 traffic-filter command (not access-group). The sequence number 10 indicates the order of evaluation; if multiple entries exist, they are processed top-down until a match is found. In real-world scenarios, failing to add a deny any statement explicitly can lead to unintended blocking of management or routing protocol traffic, such as OSPFv3 or EIGRP for IPv6, which use link-local addresses.
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 permits only IPv6 traffic from 2001:DB8:3::/48 and denies everything else — Option B is correct because an IPv6 access list, like its IPv4 counterpart, has an implicit deny all at the end. The single permit entry for source 2001:DB8:3::/48 allows only traffic from that prefix; all other IPv6 traffic is denied by the implicit deny ipv6 any any rule.
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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