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350-401 Practice Question: Which two statements about Cisco QoS…
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.
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.
Why this is correct
Correct because class maps support multiple match criteria including DSCP, CoS, IP precedence, and ACLs.
- ✓
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.
- ✗
Marking can only be applied to Layer 2 frames using CoS bits.
Why it's wrong here
Incorrect because marking can be applied at Layer 3 using DSCP or IP precedence, not just Layer 2 CoS.
- ✗
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.
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