Metering Traffic Using Token Buckets (Two-Rate Policer) - Cisco 10000 Series Configuration Manual

Chapter 6 Policing Traffic
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Metering Traffic Using Token Buckets (Two-Rate Policer)

The two-rate policer manages the maximum rate of traffic by using two token buckets: the committed
token bucket and the peak token bucket. The dual-token bucket algorithm uses user-configured values to
determine the maximum rate of traffic allowed on a queue at a given moment. In this way, the two-rate
policer can meter traffic at two independent rates: the committed information rate (CIR) and the peak
information rate (PIR).
The committed token bucket can hold bytes up to the size of the committed burst (bc) before
overflowing. This token bucket holds the tokens that determine whether a packet conforms to or exceeds
the CIR as the following describes:
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The peak token bucket can hold bytes up to the size of the peak burst (be) before overflowing. This token
bucket holds the tokens that determine whether a packet violates the PIR. A traffic stream is violating
when it causes the peak token bucket to overflow. When this occurs, the token bucket algorithm marks
the traffic stream red.
The dual-token bucket algorithm provides users with three actions for each packet—a conform action,
an exceed action, and an optional violate action. Traffic entering a queue with the two-rate policer
configured is placed into one of these categories. Within these three categories, users can decide packet
treatments. For instance, packets that conform can be configured to be sent; packets that exceed can be
configured to be sent with a decreased priority; and packets that violate can be configured to be dropped.
Figure 6-1
packet.
OL-7433-09
If the number of bytes in the exceeding bucket is less than 0, the packet violates the rate and the
router takes the violate action.
A traffic stream is conforming when the average number of bytes over time does not cause the
committed token bucket to overflow. When this occurs, the token bucket algorithm marks the traffic
stream green.
A traffic stream is exceeding when it causes the committed token bucket to overflow into the peak
token bucket. When this occurs, the token bucket algorithm marks the traffic stream yellow. The
peak token bucket is filled as long as the traffic exceeds the police rate.
shows how the two-rate policer marks a packet and assigns a corresponding action to the
Cisco 10000 Series Router Quality of Service Configuration Guide
Metering Traffic and Token Buckets
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