Two Methods For Calculating Burst-Size Limit; Time; Calculation Based On Interface Traffic Mtu; Comparison Of The Two Methods - Juniper EX9200 Features Manual

Traffic Policers Feature Guide for EX9200 Switches

Two Methods for Calculating Burst-Size Limit

Comparison of the Two Methods

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at line rate until all the accumulated tokens in the token bucket are used up. This means
that configuring a large burst size can allow too many packets to avoid rate limiting,
which can lead to a traffic rate that exceeds the bandwidth limit for an extended period
of time.
If the average rate is considered within 1 second, the rate is still below the configured
bandwidth limit. However, the downstream device might not be able to handle bursty
traffic, so some packets might be dropped.
For policers configured on MX Series, M120, and M320 routers, and EX Series switches,
configurable burst-size limit values range from 1 ms through 600 ms of traffic at the
policer rate (the configured bandwidth limit).
Because one burst size is not suitable for every traffic pattern, select the best burst size
for an interface by performing experimental configurations. For your first test configuration,
select the burst-size limit by using one of the calculation methods described in the next
two sections.
Calculation Based on Interface Bandwidth and Allowable Burst Time
If the bandwidth of the policed interface is known, the preferred method for calculating
the policer burst-size limit is based on the following values:
bandwidth —Line rate of the policed interface (in bps units)
—Allowable traffic-burst time (5 ms or longer)
burst-period
To calculate policer bandwidth in bytes:
bandwidth X burst-period / 8

Calculation Based on Interface Traffic MTU

If the bandwidth of the policed interface is unknown, calculate the policer burst-size limit
based on the following value:
—Maximum transmission unit (in bytes) for the policed interface.
interface MTU
To calculate policer bandwidth in bytes:
interface MTU Χ 10
Figure 9 on page 33 illustrates the relationship between the policer rate (the configured
bandwidth limit) and the effective burst-size limit for the two methods of calculating
the best policer burst-size limit. For the method based on interface bandwidth and
allowable burst time, the correlation is labeled 5 ms. For the method based on MTU size,
the correlation is labeled 10 MTU.
Copyright © 2016, Juniper Networks, Inc.