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Difficulty: HardQoS Per-Hop Behaviors, Classification, Marking, Queuing, and Traffic Shaping/Policing

An enterprise network engineer is designing a Quality of Service (QoS) traffic conditioning policy on a WAN edge router connecting to a service provider with a Committed Information Rate (CIR) lower than the physical link bandwidth. Which two statements accurately describe the operational mechanics and application constraints of traffic shaping versus traffic policing in this scenario?

  1. Traffic shaping buffers excess packets in a queue to smooth out bursts, resulting in a regulated transmission rate across the egress interface.Answer
  2. Traffic policing immediately drops or remarks packets exceeding the configured threshold without utilizing memory buffers.Answer
  3. C
    Traffic policing places out-of-profile burst packets into egress queues to prevent packet loss during congestion state transitions.
  4. D
    Traffic shaping can be configured on both ingress and egress directions of an interface, whereas traffic policing is strictly limited to egress traffic.

Answer

Traffic shaping buffers excess packets to smooth out traffic bursts for steady egress transmission, whereas traffic policing immediately drops or remarks packets exceeding specified limits without buffering.
Traffic shaping smooths out traffic bursts by delaying packets in buffer memory, producing a predictable egress rate. In contrast, traffic policing does not buffer packets; it acts immediately on out-of-profile traffic by dropping or remarking excess packets.

Step-by-Step Solution

1
Analyze the functional mechanism of traffic shaping.
Recognize that shaping buffers out-of-profile packets in software queues and schedules them for later transmission to yield a smooth rate.
Shaping is designed to handle bursty traffic without immediate packet drops when connecting to lower-speed CIR lines.
2
Analyze the functional mechanism of traffic policing.
Recognize that policing acts immediately on packets that exceed the token bucket criteria by either dropping them or remarking their QoS headers.
Policing enforces strict rate boundaries without delay or buffer allocations.
3
Evaluate directionality constraints for both QoS mechanisms.
Confirm that shaping is supported only outbound (egress) due to buffer management requirements, whereas policing can function inbound (ingress) and outbound (egress).
Queuing engine operations require egress scheduling control.

Key Concept

Operational differences between QoS Traffic Shaping and Traffic Policing
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Topics

QoS Per-Hop Behaviors, Classification, Marking, Queuing, and Traffic Shaping/Policing

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