The answer is CoS 0-1 to queue 1, CoS 2-3 to queue 2, CoS 4-5 to queue 3, and CoS 6-7 to queue 4. This default CoS-to-queue mapping on a Cisco switch that supports QoS is based on the 802.1p priority bits in the VLAN tag, where lower CoS values are assigned to lower-numbered egress queues (best effort) and higher CoS values to higher-numbered queues (priority traffic). For the ENCOR 350-401 exam, this mapping tests your understanding of how QoS classifies and prioritizes traffic at Layer 2, often appearing in questions about trust boundaries or queue scheduling. A common trap is confusing CoS values with DSCP or assuming all switches use the same mapping—Cisco Catalyst switches typically follow this four-queue scheme by default. To remember it, think of the pairs: 0-1 (low), 2-3 (medium-low), 4-5 (medium-high), 6-7 (high), or use the mnemonic “Lowest Two, Highest Two, Middle Pairs.”
CCNP QoS Architecture Practice Question
This 350-401 practice question tests your understanding of qos architecture. 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.
What is the default CoS-to-queue mapping on a Cisco switch that supports QoS?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
CoS 0-1 to queue 1, CoS 2-3 to queue 2, CoS 4-5 to queue 3, CoS 6-7 to queue 4
On Cisco switches that support QoS, the default Class of Service (CoS) to queue mapping distributes CoS values across four egress queues. CoS 0 and 1 are mapped to queue 1 (best effort), CoS 2 and 3 to queue 2, CoS 4 and 5 to queue 3, and CoS 6 and 7 to queue 4 (highest priority). This mapping is defined by the default trust state and is used to prioritize traffic based on the 802.1p priority bits in the VLAN tag.
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.
✓
CoS 0-1 to queue 1, CoS 2-3 to queue 2, CoS 4-5 to queue 3, CoS 6-7 to queue 4
Why this is correct
This is the default mapping for many Cisco switches.
Related concept
Read the scenario before looking for a memorised answer.
✗
CoS 0-2 to queue 1, CoS 3-5 to queue 2, CoS 6-7 to queue 3
Why it's wrong here
This is not the standard default mapping.
✗
CoS 0 to queue 1, CoS 1 to queue 2, CoS 2 to queue 3, CoS 3 to queue 4
Why it's wrong here
This is too granular; default mapping groups CoS values.
✗
All CoS values are mapped to a single queue by default.
Common exam trap: answer the scenario, not the keyword
Cisco often tests the default CoS-to-queue mapping as a memorization point, and the trap here is that candidates confuse the default mapping with a custom or logical grouping, such as assuming CoS 5 is always in the highest queue or that each CoS gets its own queue.
Detailed technical explanation
How to think about this question
The default CoS-to-queue mapping is implemented via the 'mls qos srr-queue output cos-map' command on Catalyst switches, which assigns CoS values to specific queues. Queue 1 is typically the best-effort queue with a lower priority, while queue 4 is the expedited forwarding queue for high-priority traffic like voice. In a real-world scenario, if a network engineer does not reconfigure this mapping, voice traffic (CoS 5) will be placed in queue 3 by default, which may not be the highest priority queue unless the scheduler is also tuned.
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 help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
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.
QoS Architecture — This question tests QoS Architecture — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: CoS 0-1 to queue 1, CoS 2-3 to queue 2, CoS 4-5 to queue 3, CoS 6-7 to queue 4 — On Cisco switches that support QoS, the default Class of Service (CoS) to queue mapping distributes CoS values across four egress queues. CoS 0 and 1 are mapped to queue 1 (best effort), CoS 2 and 3 to queue 2, CoS 4 and 5 to queue 3, and CoS 6 and 7 to queue 4 (highest priority). This mapping is defined by the default trust state and is used to prioritize traffic based on the 802.1p priority bits in the VLAN tag.
What should I do if I get this 350-401 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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