mediumMultiple Choice
350-401 Practice Question: Given the following configuration: interface…
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?
⚠ Common exam trap
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.
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 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.
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
Applying a policy-map with the output keyword attaches it to the egress path of the interface. This allows the router to perform congestion management tasks such as class-based weighted fair queueing (CBWFQ), low-latency queueing (LLQ), and traffic shaping on packets as they leave the interface. The queuing and scheduling decisions determine how traffic is transmitted, including bandwidth allocation and priority for real-time flows.
- ✗
The policy-map is applied to traffic entering the interface, performing classification and marking.
Why it's wrong here
An input service-policy (using the 'input' keyword) inspects packets as they arrive, enabling classification and marking of fields like IP precedence or DSCP. This is useful for metering and coloring, but it does not affect egress queuing and scheduling. Congestion management is performed on the output side, so an input policy-map cannot directly control how traffic is forwarded or queued out of the interface.
- ✗
The policy-map can only be applied if the interface is in a shutdown state.
Why it's wrong here
Cisco IOS allows a service-policy to be attached to an active, up/up interface without putting it into shutdown state. The interface's operating state does not restrict configuration, and the policy-map can be applied or removed on a live interface. While some QoS changes might cause a brief interface reset, applying a policy-map does not require a shutdown.
- ✗
The policy-map must contain a class-default with a shape command to be valid.
Why it's wrong here
A policy-map is valid even if the default class does not have a shape command. You can configure class-default with bandwidth, priority, fair-queue, or leave it with default FIFO behavior. Traffic shaping is just one possible action and is not a mandatory requirement for the policy-map to be accepted or function properly.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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