350-501 Automation and Quality of Service Practice Question
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.)
⚠ Common exam trap
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.
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)
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.
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.
- ✓
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.
- ✗
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.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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