The correct answer is that the service-policy output QOS_POLICY applies queuing and scheduling decisions to traffic exiting the interface. This is because when you use the output direction in a service-policy, the policy-map inspects packets as they leave the interface, allowing mechanisms like CBWFQ, LLQ, or shaping to manage bandwidth and latency on egress. On the ENCOR 350-401 exam, this concept tests your understanding of where QoS actions occur in the data path—a common trap is confusing output with input, where input policies typically mark or police traffic before routing. Remember that queuing and scheduling (e.g., priority queues or fair queues) only happen on the output side, as they require packets to be buffered and ordered before transmission. A useful memory tip: "Output is for ordering; Input is for marking."
350-401 QoS Architecture Practice Question
This 350-401 practice question tests your understanding of qos architecture. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
Given the following configuration:
interface GigabitEthernet0/1
service-policy output QOS_POLICY
Which statement is true about applying a service-policy in the output direction?
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 applied to traffic exiting the interface, allowing queuing and scheduling decisions.
When a service-policy is applied in the output direction, the policy-map inspects and acts on packets as they leave the interface. This allows the policy to perform queuing and scheduling decisions (e.g., CBWFQ, LLQ, shaping) on outbound traffic, which is the correct behavior for managing bandwidth and latency on egress.
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 applied to traffic exiting the interface, allowing queuing and scheduling decisions.
Why this is correct
Output service-policy controls how traffic is queued and transmitted out of the interface.
Related concept
Read the scenario before looking for a memorised answer.
✗
The policy-map is applied to traffic entering the interface, performing classification and marking.
Why it's wrong here
Input direction is used for classification and marking; output is for queuing.
✗
The policy-map can only be applied if the interface is in a shutdown state.
Why it's wrong here
Service-policy can be applied on active interfaces without shutdown.
✗
The policy-map must contain a class-default with a shape command to be valid.
Why it's wrong here
Shape is not mandatory; the policy-map can use bandwidth, priority, or fair-queue in class-default.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between input and output service-policies, where candidates mistakenly assume that output policies are used for marking or classification, when in fact those actions are typically performed on ingress.
Trap categories for this question
Command / output trap
Input direction is used for classification and marking; output is for queuing.
Detailed technical explanation
How to think about this question
Under the hood, output service-policies leverage the Modular QoS CLI (MQC) to attach a policy-map to the egress hardware queue structure. For example, on a Cisco Catalyst switch, an output policy can enable Shaped Round Robin (SRR) or Weighted Tail Drop (WTD) to manage egress buffering. In real-world scenarios, this is critical for ensuring voice traffic (marked EF) is placed into a strict priority queue (LLQ) while data traffic is shaped to avoid oversubscription on a WAN link.
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 350-401 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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 350-401 question in full detail.
QoS Architecture — This question tests QoS Architecture — 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 applied to traffic exiting the interface, allowing queuing and scheduling decisions. — When a service-policy is applied in the output direction, the policy-map inspects and acts on packets as they leave the interface. This allows the policy to perform queuing and scheduling decisions (e.g., CBWFQ, LLQ, shaping) on outbound traffic, which is the correct behavior for managing bandwidth and latency on egress.
What should I do if I get this 350-401 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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