Traffic Policing

• Used to meter a packet flow rate.
  • Marks packets that exceed metered rate.
  • Drop is a mark action.
• Normally an ingress operation.
  • PE ingress from CE for example.
• Policing has two parameters
  • Metering rate – CIR
  • Averaging interval – Tc

• Larger Tc the more bursting is allowed
  • Bc = CIR*Tc is max burst size allowed momentarily (in bytes)
• Be – excessive burst
  • Max amount of bytes allowed above Bc during Tc.
  • Only allowed if Bc was not fully utilized before.

• Single-Rate Policing Syntax
  • Configuration
    • ‘police <cir> <CIR> <Bc> <Be>’
    • CIR in bps while bursts are in bytes
  • Applied to an MQC class
    • Three actions (colors): conform, exceed, violate
    • Exceed: flow exceeds Bc but under Bc+Be
    • Violate: burst size exceeds Bc+Be

• Dual-Rate Policing Syntax
  • Configuration
    • ‘police cir <CIR> bc <Bc> pir <PIR> be <Be>’
  • Normally used to implement two-rate access.
    • Customer is guaranteed CIR.
    • Allowed to send up to PIR
    • Traffic between PIR and CIR are marked
      • Lower DSCP

• Shaping and Policing Together
  • Operations are Complimentary
    • Shaping is done egress.
    • Policing is done ingress.
  • Parameters should match
    • Shaping is set to match policing
    • Same CIR, Bc and Be
      • Policing values could be greater.

Note:

• Traffic policing CAN be done on both input and output queue.
• Traffic Policing is used to REMARK traffic that exceeds rate.
  • Often times that mark is going to drop, but not always.