350-501 Networking Practice Question
Which QoS mechanism marks packets at the edge of the network to classify traffic into different service classes?
⚠ Common exam trap
Cisco often tests the distinction between marking and policing, where candidates mistakenly think policing is used for classification because it can re-mark packets, but the question specifically asks for the mechanism that marks at the edge to classify traffic, which is marking itself, not policing.
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
✓
Marking
Marking is the QoS mechanism that sets the Differentiated Services Code Point (DSCP) or IP Precedence bits in the packet header at the ingress edge of the network. This classification allows downstream devices to apply per-hop behaviors (PHBs) based on the marked value, as defined in RFC 2474 and RFC 2597. Unlike queuing, shaping, or policing, marking does not delay or drop packets; it only modifies the packet header to indicate the desired service class.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Queuing
Why it's wrong here
Queuing manages packet scheduling; does not mark.
- ✗
Shaping
Why it's wrong here
Shaping buffers and smooths traffic rate; does not mark.
- ✗
Policing
Why it's wrong here
Policing drops or re-marks traffic; its primary function is not marking at edge.
- ✓
Marking
Why this is correct
Marking sets the QoS bits in the packet header.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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