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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.)
⚠ Common exam trap
Many candidates confuse the roles of class maps and policy maps: class maps classify, policy maps apply actions like marking. Candidates often mistakenly think class maps can apply marking actions.
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.
Option A is correct because a Cisco class map (defined with the class-map command and used inside a policy map) can match traffic using criteria such as DSCP values, CoS bits, IP precedence, or ACLs (match dscp, match cos, match precedence, match access-group), which is exactly how classification is performed in MQC. Option B is correct because QoS marking is best done as close to the traffic source as possible, typically at the access layer, so that the DSCP/CoS value is preserved and honored by every downstream device without reclassification. Option C is incorrect because marking is not limited to Layer 2 CoS; devices can also set Layer 3 DSCP and IP precedence (and MPLS EXP), so CoS-only marking is false. Option D is incorrect because tail drop is a congestion avoidance/queue management mechanism, not a marking function, and marking itself is not a congestion avoidance mechanism. Option E is incorrect because a policy map (not a class map) applies marking actions to classified traffic; the class map only identifies/matches the traffic.
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
A class map defines the match criteria for traffic classification, and Cisco IOS supports matching on Layer 2 CoS, Layer 3 DSCP, IP precedence, and ACL entries within the same class map. This satisfies the stem's requirement for accurate classification and marking statements, since classification must identify traffic before marking policies apply.
- ✓
Marking should be performed as close to the source as possible, typically at the access layer.
Why this is correct
Marking as close to the source as possible, typically at the access layer, preserves classification detail before congestion or trust-boundary re-marking erodes it. Edge devices can then apply per-hop behaviour using the original DSCP or CoS values, satisfying the stem's requirement for accurate, scalable QoS treatment across the network core.
- ✗
Marking can only be applied to Layer 2 frames using CoS bits.
Why it's wrong here
Marking applies at both Layer 2 (CoS in 802.1Q) and Layer 3 (DSCP, IP precedence), plus MPLS EXP, so restricting it to CoS bits is false. The temptation is that CoS is the classic Layer 2 marking field, but DSCP marking on IP packets is equally valid and common.
- ✗
Marking is a congestion avoidance mechanism that uses tail drop.
Why it's wrong here
Marking sets classification values in packet headers; it does not drop traffic. Tail drop is a congestion-avoidance queueing mechanism, and WRED is its weighted variant. The confusion comes from marking and queueing both appearing in QoS policy maps, yet they act at different stages.
- ✗
A class map is used to apply marking actions to classified traffic.
Why it's wrong here
Class maps only match and classify traffic; marking actions are attached to policy maps, not class maps. The confusion arises because class maps are configured inside policy maps, so they appear adjacent to marking commands, but a class map alone cannot set DSCP, CoS or IP precedence values.
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
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