Juniper EX9200 Features Manual page 44

Traffic Policers Feature Guide for EX9200 Switches
26
NOTE: For single-rate two-color policers only, you can also specify the
bandwidth limit as a percentage of either the physical interface port speed
or the configured logical interface shaping rate by using the
bandwidth-percent percentage statement. You cannot configure a policer
to use bandwidth percentage for aggregate, tunnel, or software interfaces.
Use the following command to set the policer conditions:
user@router# set firewall policer <policer name> if-exceeding ?
Possible completions:
<[Enter]> Execute this command
+ apply-groups Groups from which to inherit configuration data
+ apply-groups-except Don't inherit configuration data from these groups
bandwidth-limit Bandwidth limit (8000..100000000000 bits per second)
bandwidth-percent Bandwidth limit in percentage (1..100 percent)
burst-size-limit Burst size limit (1500..100000000000 bytes)
| Pipe through a command
The bandwidth limit parameter is used to determine the average rate limit applied to the
traffic, while the burst-size parameter is used to allow for short periods of traffic bursting
(back-to-back traffic at average rates that exceed the configured bandwidth limit). Once
you apply a set of policer configuration settings (bandwidth limit and burst size), the
configured values are adjusted to hardware programmable values. The conversion
adjustment introduced is normally less than 1 percent of the configured bandwidth limit.
This adjustment is needed because the software allows you to configure the bandwidth
limit and burst size to any value within the specified ranges, but those values must be
adjusted to the nearest value that can be programmed in the hardware.
The policer bandwidth limit configuration in the hardware is represented by two values:
the credit update frequency and the credit size. The credit update frequency is used by
the hardware to determine how frequently tokens (bits of unused bandwidth) are added
to the token bucket. The credit size is based on the number of tokens that can fit in the
token bucket. The MX Series, M120, M320 routers, and EX Series switches contain a set
of credit update frequencies instead of having a single credit update frequency to minimize
the adjustment difference from the configured bandwidth limit and to support a wide
range of policer bandwidth rates (from 40 Kbps to 40 Gbps). One of the frequencies is
used to program the policer (bandwidth limit and burst size) in the hardware.
The burst size is based on the overall traffic load and allows bursts of traffic to exceed
the configured bandwidth limit. A policer with a large burst size effectively disables the
configured bandwidth limit function, so the burst size must be relative to the configured
bandwidth limit. You need to consider the traffic patterns in your network before
determining the burst size. For more information about determining burst size, see
"Determining Proper Burst Size for Traffic Policers" on page
The configured burst size is adjusted in the hardware to a value that is based on the
configured bandwidth limit. The burst size extends the configured bandwidth limit for
bursty traffic that exceeds the configured bandwidth limit.
When a policer is applied to the traffic at an interface, the initial capacity for traffic bursting
is equal to the number of bytes specified in the burst-size-limit statement.
30.
Copyright © 2016, Juniper Networks, Inc.