Policing and Shaping

This chapter looks at the fundamental mechanics of policer and shaper tools. Policers are implemented using the concept of a token bucket, while shapers use leaky buckets. The chapter explains both and compares the two in terms of applicability and differences regarding how to use them to deal with traffic burstiness and excess traffic. A token bucket operates using the concept of credits. The chapter considers that the traffic crosses the policer at a perfect flat rate, without any bursts, and also that the traffic rate is always below the policer bandwidth limit parameter. Dual‐rate policers are popular and are commonly implemented together with the metering tool. The existence of excess traffic is commonly associated with the oversubscription phenomenon, the concept of having a logical interface with a certain bandwidth value that during some periods of time may receive more traffic than it can cope with.