The answer is that Catalyst 2960-X switches do not support VLAN matching in a QoS class-map, making the marking configuration ineffective. This limitation exists because these switches only allow classification based on CoS, DSCP, or IP precedence within a class map, not on Layer 2 VLAN IDs. On the ENCOR 350-401 exam, this tests your understanding of platform-specific QoS capabilities, often appearing as a trick where a candidate assumes all Catalyst switches support VLAN-based classification. A common trap is to overlook that the 2960-X is a fixed-configuration switch with reduced QoS features compared to the 3850 or 9300 series. To remember this, think: "2960-X can't match the VLAN, only the LAN's mark."
CCNP QoS Practice Question
This 350-401 practice question tests your understanding of qos. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 is configuring QoS on a Cisco Catalyst 2960-X switch to support marking of traffic based on VLAN. The switch has two VLANs: VLAN 10 (voice) and VLAN 20 (data). The engineer wants to mark all traffic from VLAN 10 with CoS 5 and all traffic from VLAN 20 with CoS 0. The engineer applies a policy map that matches on VLAN using a class map. However, the marking is not being applied. What is the most likely reason?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The switch does not support VLAN-based classification in QoS
The correct answer is that Catalyst 2960-X switches do not support matching on VLAN in a class map for QoS; they only support matching on CoS, DSCP, or IP precedence. The engineer must use a different matching criterion.
Key principle: A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
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 switch does not support VLAN-based classification in QoS
Why this is correct
Correct because Catalyst 2960-X switches lack the ability to match on VLAN in a class map; they rely on CoS or DSCP.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Access ports place end devices into a single VLAN.
✗
The policy map is applied in the wrong direction
Why it's wrong here
Incorrect because direction does not affect the ability to match on VLAN; the feature is simply not supported.
✗
The class map should use 'match access-group' instead of 'match vlan'
Why it's wrong here
Incorrect because while ACLs can match on VLAN, the switch does not support VLAN-based ACLs for QoS classification.
✗
The switch requires the 'mls qos' command to be enabled globally
Why it's wrong here
Incorrect because 'mls qos' is required for QoS, but even with it enabled, VLAN-based matching is not supported.
Common exam traps
Common exam trap: an active trunk can still block the VLAN you need
A trunk being up does not prove every VLAN is crossing it. Check allowed VLAN lists, native VLAN mismatch, VLAN existence and access-port assignment.
Detailed technical explanation
How to think about this question
VLAN questions usually combine access-port and trunking clues. The key is to identify whether the issue is local to one switchport, caused by the trunk, or caused by the VLAN not existing where it needs to exist.
KKey Concepts to Remember
Access ports place end devices into a single VLAN.
Trunk ports carry multiple VLANs between switches.
Allowed VLAN lists decide which VLANs can cross a trunk.
Native VLAN mismatch can create confusing symptoms.
TExam Day Tips
→Use show vlan brief to verify access VLANs.
→Use show interfaces trunk to verify trunk state and allowed VLANs.
→Do not treat every same-VLAN issue as a routing problem.
Key takeaway
A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
Real-world example
How this comes up in practice
A help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
What to study next
Got this wrong? Here's your next step.
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 350-401 questions on switching, trunking, and access-port configuration.
QoS — This question tests QoS — Access ports place end devices into a single VLAN..
What is the correct answer to this question?
The correct answer is: The switch does not support VLAN-based classification in QoS — The correct answer is that Catalyst 2960-X switches do not support matching on VLAN in a class map for QoS; they only support matching on CoS, DSCP, or IP precedence. The engineer must use a different matching criterion.
What should I do if I get this 350-401 question wrong?
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 350-401 questions on switching, trunking, and access-port configuration.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Access ports place end devices into a single VLAN.
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