CAR Operation

CAR examines traffic received on an interface or a subset of that traffic selected by access list criteria. CAR compares the rate of the traffic to a configured token bucket and takes action based on the result. For example, CAR will drop the packet or rewrite the IP precedence by resetting the type of service (ToS) bits.

CAR can be configured to send, drop, or set precedence.

Aspects of CAR rate limiting include the following:

• Matching criteria

• Conform and exceed actions

• Multiple rate policies

CAR utilizes a token bucket measurement, operating as follows:

• Tokens are inserted into the bucket at the committed rate.

• The depth of the bucket is the burst size.

• Traffic arriving at the bucket when sufficient tokens are available is said to conform, and the corresponding number of tokens is removed from the bucket.

• If a sufficient number of tokens is not available, then the traffic is said to exceed.

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