The answer is that the VoIP traffic is not marked with DSCP EF from the source. This is correct because the 'match ip dscp ef' command in a QoS class-map evaluates the DSCP value already present in the incoming packet; if the source device, such as an IP phone, has not set DSCP 46, the class map will not match, and the policy cannot apply any re-marking. On the Cisco SPCOR 350-501 exam, this scenario tests your understanding that classification happens before marking—a common trap is assuming the router will mark unmarked traffic based on the match statement alone. Remember the key principle: you cannot re-mark what you have not first matched. A useful memory tip is “match first, mark second”—the class-map is a gatekeeper, not a painter.
350-501 Automation and Quality of Service Practice Question
This 350-501 practice question tests your understanding of automation and quality of service. 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.
A network administrator configures a class map to match VoIP traffic using 'match ip dscp ef' on a Cisco router. However, the QoS policy is not applying the expected marking to VoIP packets. What is a possible reason?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The VoIP traffic is not marked with DSCP EF from the source.
Option B is correct because the 'match ip dscp ef' command in the class map checks the DSCP value already present in the incoming VoIP packets. If the source device (e.g., an IP phone) does not mark the packets with DSCP EF (46), the class map will not match, and the QoS policy will not apply the expected marking. The policy can only re-mark packets that are already matched by the class map.
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 is applied in the output direction instead of input.
Why it's wrong here
The direction would affect all traffic, not just VoIP.
✓
The VoIP traffic is not marked with DSCP EF from the source.
Why this is correct
If the source does not set DSCP EF, the match will fail and the traffic will not be classified.
Related concept
Read the scenario before looking for a memorised answer.
✗
The policy is applied to the wrong interface.
Why it's wrong here
If the policy were on the wrong interface, no traffic would be affected.
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that a QoS policy can re-mark traffic regardless of the original packet markings, when in fact the class map must first match the existing DSCP value for the policy to take effect.
Detailed technical explanation
How to think about this question
DSCP EF (Expedited Forwarding, value 46) is defined in RFC 3246 for low-loss, low-latency traffic like VoIP. The 'match ip dscp' command matches the DSCP field in the IP header, which is set by the source device; if the source does not set it, the router cannot match it. In real-world deployments, IP phones often mark DSCP EF automatically, but misconfigured endpoints or intermediate devices (e.g., switches stripping or not setting DSCP) can cause this issue, requiring trust boundaries to be configured correctly.
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.
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 VoIP traffic is not marked with DSCP EF from the source. — Option B is correct because the 'match ip dscp ef' command in the class map checks the DSCP value already present in the incoming VoIP packets. If the source device (e.g., an IP phone) does not mark the packets with DSCP EF (46), the class map will not match, and the QoS policy will not apply the expected marking. The policy can only re-mark packets that are already matched by the class map.
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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Question Discussion
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