350-501 Services Practice Question
Exhibit
interface GigabitEthernet0/0/0/0 ipv4 address 10.1.1.1 255.255.255.252 service-policy output QOS_POLICY ! class-map match-any REALTIME match precedence 5 match dscp ef ! policy-map QOS_POLICY class REALTIME priority level 1 police rate percent 10 class class-default bandwidth remaining ratio 1
Refer to the exhibit. A service provider is applying this QoS policy on a PE-CE interface. The business customer complains that voice traffic (marked with DSCP EF) experiences drops during congestion. What is the likely cause?
⚠ Common exam trap
Cisco often tests the distinction between priority queuing (which provides low latency) and policing (which enforces a rate limit), leading candidates to overlook that a police rate in a priority class can cause drops even when the priority queue is not congested.
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 police rate under the REALTIME class is limiting voice traffic to 10% of bandwidth.
The REALTIME class uses the 'police' command to enforce a rate of 10% of the interface bandwidth. When voice traffic marked DSCP EF exceeds this policed rate, packets are dropped, even though the class is configured with priority queuing. The police rate is the bottleneck, not the priority queue itself.
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 police rate under the REALTIME class is limiting voice traffic to 10% of bandwidth.
Why this is correct
Policing drops traffic exceeding 10%.
- ✗
The priority level is set too low; voice should be priority level 4.
Why it's wrong here
Priority level only affects the order of multiple priority queues; level 1 is highest.
- ✗
The 'bandwidth remaining ratio' command under class-default is starving the priority queue.
Why it's wrong here
The priority queue is not affected by bandwidth remaining ratio.
- ✗
The policy is applied in the output direction; it should be input.
Why it's wrong here
Output direction is correct for shaping/policing egress traffic.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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