- A
EXP bits are always copied from the IP DSCP at the ingress PE.
Why wrong: Only in Uniform model; in Pipe models, EXP is set separately.
- B
In Pipe model, the egress PE uses EXP bits for queuing.
Why wrong: In Pipe, egress uses EXP; in Short Pipe, egress uses IP DSCP.
- C
The MPLS EXP field is 6 bits, same as DSCP.
Why wrong: EXP is 3 bits (8 values).
- D
In Short Pipe model, the egress PE uses the original IP DSCP for queuing decisions, not the EXP.
Short Pipe uses IP DSCP at egress, not EXP.
Question 30 of 1,000
350-501 Automation and Quality of Services Practice Question
This 350-501 practice question tests your understanding of automation and quality of services. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
In an SP MPLS core, a PE router maps incoming DSCP values to MPLS EXP bits. Which statement about EXP marking is accurate when using the DiffServ Tunneling Model?
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
✓
In Short Pipe model, the egress PE uses the original IP DSCP for queuing decisions, not the EXP.
In the DiffServ Tunneling Model, the Short Pipe model specifically instructs the egress PE to ignore the MPLS EXP bits for queuing and instead use the original IP DSCP value. This preserves the end-to-end QoS marking across the MPLS core, making option D correct. The Pipe model, by contrast, uses the EXP bits at the egress PE, which is why option B is incorrect.
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.
- ✗
EXP bits are always copied from the IP DSCP at the ingress PE.
Why it's wrong here
Only in Uniform model; in Pipe models, EXP is set separately.
- ✗
In Pipe model, the egress PE uses EXP bits for queuing.
Why it's wrong here
In Pipe, egress uses EXP; in Short Pipe, egress uses IP DSCP.
- ✗
The MPLS EXP field is 6 bits, same as DSCP.
Why it's wrong here
EXP is 3 bits (8 values).
- ✓
In Short Pipe model, the egress PE uses the original IP DSCP for queuing decisions, not the EXP.
Why this is correct
Short Pipe uses IP DSCP at egress, not EXP.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between Pipe and Short Pipe models, where candidates mistakenly think the egress PE always uses EXP bits for queuing, but in Short Pipe the egress PE reverts to the original IP DSCP.
Detailed technical explanation
How to think about this question
The DiffServ Tunneling Model defines three modes: Uniform, Pipe, and Short Pipe. In Short Pipe, the egress PE removes the MPLS label and uses the original IP DSCP for queuing, while the EXP bits are only relevant within the MPLS core for PHB scheduling. This model is commonly used when the service provider wants to isolate core QoS from customer markings, ensuring the customer's DSCP is preserved end-to-end.
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.
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Automation and Quality of Services — study guide chapter
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FAQ
Questions learners often ask
What does this 350-501 question test?
Automation and Quality of Services — This question tests Automation and Quality of Services — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: In Short Pipe model, the egress PE uses the original IP DSCP for queuing decisions, not the EXP. — In the DiffServ Tunneling Model, the Short Pipe model specifically instructs the egress PE to ignore the MPLS EXP bits for queuing and instead use the original IP DSCP value. This preserves the end-to-end QoS marking across the MPLS core, making option D correct. The Pipe model, by contrast, uses the EXP bits at the egress PE, which is why option B is incorrect.
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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Last reviewed: Jul 4, 2026
This 350-501 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-501 exam.
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