Traffic Shaping

• Goal is to normalize traffic flow
  • Smooth out bursts
  • Prepare traffic for ingress policing.
  • Delay and Queue exceeding traffic.
• Terminology
  • Access Rate – AR
    • Physical port speed
  • Committed Information Rate – CIR
    • Average rate the shaper is targetting.
  • Time Committed – Tc
    • Time interval in ms to emit traffic bursts
    • Bursts always emitted at Access Rate (AR)
  • Burst Committed – Bc
    • Amount of bits that could be sent every Tc
  • Burst Excessive – Be
    • Amount of bits over Bc that could be sent during Tc
    • Must be accumulated by idle periods.

• Modular QoS Command line (MQC) Syntax
  • Configuration via MQC
    • ‘shape average <cir> [Bc][Be]
    • Tc is found implicitly as Bc/CIR
  • Default shaper queue is FIFO.
    • Can be turned into HQF by associating a child policy-map with shaped class.
    • Specify HQF settings in the child-policy
      • ie. nested policies.
        • ie. shaping could be on outside policy, fancy queueing is referenced in outer policy via ‘service-policy’ command.

Configuration:

Create new access-list referencing ICMP:

Create new class-map that references access-list ‘ICMP’:

Create new Policy-map that references Class-map ‘ICMP’:

Under the Policy-map ‘SHAPER’ we’re saying the shape average is target bit rate.

And lastly, apply to the desired interface.

Now when doing a normal ping and high repeat ping out interface gig0/3, we’ll see the latency is very low, then very high.

Our normal ping has an average latency to 4.4.4.4 of 3ms. The high repeat ping has an average latency of 689ms.