- A
A class map can match traffic based on DSCP, CoS, IP precedence, or ACL.
Correct because class maps support multiple match criteria including DSCP, CoS, IP precedence, and ACLs.
- B
Marking should be performed as close to the source as possible, typically at the access layer.
Correct because marking at the access layer ensures consistent treatment throughout the network.
- C
Marking can only be applied to Layer 2 frames using CoS bits.
Why wrong: Incorrect because marking can be applied at Layer 3 using DSCP or IP precedence, not just Layer 2 CoS.
- D
Marking is a congestion avoidance mechanism that uses tail drop.
Why wrong: Incorrect because marking is a classification tool, not a congestion avoidance mechanism; tail drop is used in queuing.
- E
A class map is used to apply marking actions to classified traffic.
Why wrong: Incorrect because class maps only define match criteria; policy maps apply actions like marking.
350-401 QoS Architecture Practice Question
This 350-401 practice question tests your understanding of qos architecture. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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.
Which two statements about Cisco QoS classification and marking are true? (Choose two.)
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
A class map can match traffic based on DSCP, CoS, IP precedence, or ACL.
Classification identifies traffic based on fields like DSCP, CoS, or IP precedence. Marking sets the DSCP or CoS value for subsequent actions. The 'class-map' command matches traffic, and 'policy-map' applies marking. Option A is correct because class maps can match on DSCP, CoS, IP precedence, or even ACLs. Option B is correct because marking is typically done at the trust boundary (access layer) to set the initial QoS marking. Option C is incorrect because marking is not limited to Layer 2; Layer 3 DSCP marking is common. Option D is incorrect because marking does not use tail drop; tail drop is a congestion avoidance mechanism. Option E is incorrect because class maps do not apply actions; policy maps do.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
A class map can match traffic based on DSCP, CoS, IP precedence, or ACL.
- ✓
Marking should be performed as close to the source as possible, typically at the access layer.
Why this is correct
Correct because marking at the access layer ensures consistent treatment throughout the network.
Related concept
Standard ACLs match source addresses.
- ✗
Marking can only be applied to Layer 2 frames using CoS bits.
- ✗
Marking is a congestion avoidance mechanism that uses tail drop.
Why it's wrong here
Incorrect because marking is a classification tool, not a congestion avoidance mechanism; tail drop is used in queuing.
- ✗
A class map is used to apply marking actions to classified traffic.
Why it's wrong here
Incorrect because class maps only define match criteria; policy maps apply actions like marking.
Common exam traps
Common exam trap: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
- Standard ACLs match source addresses.
- Extended ACLs can match source, destination, protocol and ports.
- The first matching ACL entry is used.
- There is usually an implicit deny at the end.
TExam Day Tips
- Check inbound versus outbound direction.
- Read the ACL from top to bottom.
- Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Real-world example
How this comes up in practice
A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
What to study next
Got this wrong? Here's your next step.
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related 350-401 ACL questions on filtering logic and placement.
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FAQ
Questions learners often ask
What does this 350-401 question test?
QoS Architecture — This question tests QoS Architecture — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: A class map can match traffic based on DSCP, CoS, IP precedence, or ACL. — Classification identifies traffic based on fields like DSCP, CoS, or IP precedence. Marking sets the DSCP or CoS value for subsequent actions. The 'class-map' command matches traffic, and 'policy-map' applies marking. Option A is correct because class maps can match on DSCP, CoS, IP precedence, or even ACLs. Option B is correct because marking is typically done at the trust boundary (access layer) to set the initial QoS marking. Option C is incorrect because marking is not limited to Layer 2; Layer 3 DSCP marking is common. Option D is incorrect because marking does not use tail drop; tail drop is a congestion avoidance mechanism. Option E is incorrect because class maps do not apply actions; policy maps do.
What should I do if I get this 350-401 question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related 350-401 ACL questions on filtering logic and placement.
What is the key concept behind this question?
Standard ACLs match source addresses.
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Last reviewed: Jun 18, 2026
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