- A
The policy-map is not applied to the correct interface direction (input vs output)
DSCP marking can be done inbound or outbound; applying to the wrong direction means the marking never occurs on the traffic path.
- B
The class-map is using the wrong match criteria (e.g., DSCP value)
If the class-map does not match the expected traffic, the marking action is never applied to that traffic.
- C
The policy-map is applied to a loopback interface
Why wrong: Loopback interfaces do not carry real traffic; packets are not forwarded through them.
- D
The marking is configured under the wrong policy-map
Why wrong: If marking is in the wrong policy, that policy might not even be applied to the interface.
- E
The device is running out of TCAM space
Why wrong: TCAM exhaustion would affect performance but would not silently cause missing markings; errors would appear.
Quick Answer
The answer is that DSCP markings are not being applied due to two common misconfigurations: the class-map using the wrong match criteria, or the policy-map being applied in the wrong direction. When a class-map matches on an incorrect DSCP value or protocol, the traffic never enters the correct traffic class, so the marking action in the policy-map is never executed. Similarly, a marking policy must be applied in the correct direction—ingress or egress—relative to the traffic flow; if you intend to mark packets as they enter an interface but apply the policy to the egress direction, the packets bypass the marking logic entirely. On the Cisco SPCOR / CCNP Service Provider Core 350-501 exam, this concept tests your understanding of the MQC (Modular QoS CLI) workflow and the critical role of policy-map application direction. A common trap is assuming that marking can occur on egress without verifying that the policy is actually attached to the correct interface and direction. Remember the memory tip: “Match first, then direct—wrong class or wrong way, DSCP will stay.”
350-501 Automation and Quality of Service Practice Question
This 350-501 practice question tests your understanding of automation and quality of service. 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.
During QoS troubleshooting, you capture traffic and see that DSCP markings are not being applied as configured. Which two common misconfigurations could cause this? (Choose two.)
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 policy-map is not applied to the correct interface direction (input vs output)
Option A is correct because a policy-map must be applied in the correct direction (input or output) for the marking to take effect. If a marking policy is applied to the wrong direction, the packets will not be processed by the policy, and DSCP values will remain unchanged. This is a common misconfiguration when the intended marking should occur on ingress but the policy is applied to egress, or vice versa.
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 policy-map is not applied to the correct interface direction (input vs output)
Why this is correct
DSCP marking can be done inbound or outbound; applying to the wrong direction means the marking never occurs on the traffic path.
Related concept
Read the scenario before looking for a memorised answer.
- ✓
The class-map is using the wrong match criteria (e.g., DSCP value)
Why this is correct
If the class-map does not match the expected traffic, the marking action is never applied to that traffic.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The policy-map is applied to a loopback interface
Why it's wrong here
Loopback interfaces do not carry real traffic; packets are not forwarded through them.
- ✗
The marking is configured under the wrong policy-map
Why it's wrong here
If marking is in the wrong policy, that policy might not even be applied to the interface.
- ✗
The device is running out of TCAM space
Why it's wrong here
TCAM exhaustion would affect performance but would not silently cause missing markings; errors would appear.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between input and output policy application, as candidates may overlook that a marking policy applied to the wrong direction will silently fail to modify DSCP values.
Detailed technical explanation
How to think about this question
DSCP marking is often performed using a 'set dscp' command inside a policy-map class. The policy-map must be applied to an interface in the correct direction (service-policy input or output) for the marking to occur at that stage of packet processing. In Cisco IOS, marking on ingress is common for trust boundaries, while egress marking is used for remarking before leaving the router. Misapplying the direction is a frequent error because engineers may confuse where in the path the marking should happen.
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 practitioner preparing for the 350-501 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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Automation and Quality of Service — study guide chapter
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FAQ
Questions learners often ask
What does this 350-501 question test?
Automation and Quality of Service — This question tests Automation and Quality of Service — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The policy-map is not applied to the correct interface direction (input vs output) — Option A is correct because a policy-map must be applied in the correct direction (input or output) for the marking to take effect. If a marking policy is applied to the wrong direction, the packets will not be processed by the policy, and DSCP values will remain unchanged. This is a common misconfiguration when the intended marking should occur on ingress but the policy is applied to egress, or vice versa.
What should I do if I get this 350-501 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: Jun 25, 2026
This 350-501 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 350-501 exam.
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