- A
IPv6 access-list with the 'flow-label' option
The 'flow-label' keyword allows matching the 20-bit Flow Label field in the IPv6 header.
- B
IPv6 prefix-list
Why wrong: Prefix-lists match on prefixes, not flow labels.
- C
IPv6 route-map with match ipv6 address
Why wrong: Route-maps can reference access-lists but do not directly match flow labels.
- D
IPv6 uRPF
Why wrong: uRPF checks routing table reachability, not flow labels.
Question 1,514 of 2,152
How to Match IPv6 Flow Label in Access Lists
This 300-410 practice question tests your understanding of ipv6 traffic filtering and urpf. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
Which IPv6 traffic filter can be used to match traffic based on the Flow Label field?
Quick Answer
The answer is an IPv6 access-list configured with the flow-label keyword. This is correct because the IPv6 Flow Label field is a 20-bit value in the IPv6 header designed for per-flow packet classification, and Cisco IOS supports matching this field directly within an extended IPv6 ACL using the `flow-label` parameter. On the Cisco CCNP ENARSI 300-410 exam, this tests your understanding of advanced IPv6 ACL features beyond basic source/destination matching; a common trap is assuming only QoS policies can inspect the flow label, but the ACL match is a distinct filtering capability. Remember that the flow-label match is optional and must be explicitly specified in the access-list entry, often combined with other match criteria like protocol or port. A useful memory tip: think of the flow label as a “traffic fingerprint” — you match it with the `flow-label` keyword in the ACL, not with a class-map or route-map.
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
✓
IPv6 access-list with the 'flow-label' option
Option A is correct because the IPv6 access-list supports the 'flow-label' keyword, which allows matching packets based on the 20-bit Flow Label field in the IPv6 header. This field is defined in RFC 2460 and is used for per-flow processing, such as QoS or load balancing, without needing to inspect upper-layer headers.
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.
- ✓
IPv6 access-list with the 'flow-label' option
Why this is correct
The 'flow-label' keyword allows matching the 20-bit Flow Label field in the IPv6 header.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
IPv6 prefix-list
Why it's wrong here
Prefix-lists match on prefixes, not flow labels.
- ✗
IPv6 route-map with match ipv6 address
Why it's wrong here
Route-maps can reference access-lists but do not directly match flow labels.
- ✗
IPv6 uRPF
Why it's wrong here
uRPF checks routing table reachability, not flow labels.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between packet-matching tools (access-lists) and route-matching tools (prefix-lists, route-maps), leading candidates to incorrectly select prefix-lists or route-maps when the question involves header fields like Flow Label.
Detailed technical explanation
How to think about this question
The Flow Label field is a 20-bit field in the IPv6 header that can be set by a source to label packets belonging to the same flow, enabling intermediate routers to identify and process them as a group without deep packet inspection. In real-world scenarios, this is particularly useful for traffic engineering or QoS policies where you want to treat all packets from a video stream identically, and the 'flow-label' option in an IPv6 ACL allows granular matching for such purposes.
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: IPv6 access-list with the 'flow-label' option — Option A is correct because the IPv6 access-list supports the 'flow-label' keyword, which allows matching packets based on the 20-bit Flow Label field in the IPv6 header. This field is defined in RFC 2460 and is used for per-flow processing, such as QoS or load balancing, without needing to inspect upper-layer headers.
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
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.
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