Juniper EX9200 Series, Features Manual

Page: 221 / 278

burst-size-limit (Policer)
Syntax burst-size-limit bytes;
Hierarchy Level [edit dynamic-profiles profile-name firewall policer policer-name if-exceeding ],
[edit firewall policer policer-name if-exceeding ],
[edit logical-systems logical-system-name policer policer-name if-exceeding ]
Release Information Statement introduced before Junos OS Release 7.4.
Support at the
[edit dynamic-profiles ... if-exceeding]
hierarchy level introduced in Junos
OS Release 11.4.
Statement introduced in Junos OS Release 12.3R2 for EX Series switches.
Description For a single-rate two-color policer, configure the burst size as a number of bytes. The
burst size allows for short periods of traffic bursting (back-to-back traffic at average
rates that exceed the configured bandwidth limit). Single-rate two-color policing uses
the
single token bucket algorithm to measure traffic-flow conformance to a two-color
policer rate limit.
Traffic at the interface that conforms to the bandwidth limit is categorized green. Traffic
that exceeds the specified rate is also categorized as green provided that sufficient tokens
remain in the single token bucket. Packets in a green flow are implicitly marked with
low
packet loss priority and then passed through the interface.
Traffic that exceeds the specified rate when insufficient tokens remain in the single token
bucket is categorized red. Depending on the configuration of the two-color policer, packets
in a red traffic flow might be implicitly discarded; or the packets might be re-marked with
a specified forwarding class, a specified PLP, or both, and then passed through the
interface.
The burst size extends the function of the bandwidth limit (configured using either the
bandwidth-limit bps statement or the bandwidth-percent percentage statement) to allow
bursts of traffic up to a limit based on the overall traffic load:
•
When a single-rate two-color policer is applied to the input or output traffic at an
interface, the initial capacity for traffic bursting is equal to the number of bytes specified
by this statement.
•
During periods of relatively low traffic (traffic that arrives at or departs from the interface
at overall rates below the token arrival rate), unused tokens accumulate in the bucket,
but only up to the configured token bucket depth.
Single-rate two-color policing allows bursts of traffic for short periods, whereas single-rate
and two-rate three-color policing allows more sustained bursts of traffic.
Hierarchical policing is a form of two-color policing that applies different policing actions
based on whether the packets are classified for expedited forwarding (EF) or for a lower
priority. You apply a hierarchical policer to ingress Layer 2 traffic to allows bursts of EF
traffic for short period and bursts of non-EF traffic for short periods, with EF traffic always
taking precedence over non-EF traffic.
203 Copyright © 2016, Juniper Networks, Inc.
Chapter 18: Configuration Statements