.TH "Policing action in tc" 8 "20 Jan 2015" "iproute2" "Linux"

.SH NAME

police - policing action

.SH SYNOPSIS

.in +8

.ti -8

.BR tc " ... " "action police"

.BI rate " RATE " burst

.IR BYTES [\fB/ BYTES "] ["

.B mtu

.IR BYTES [\fB/ BYTES "] ] ["

.BI peakrate " RATE"

] [

.BI overhead " BYTES"

] [

.BI linklayer " TYPE"

] [

.IR CONTROL " ]"

.ti -8

.BR tc " ... " filter " ... [ " estimator

.IR "SAMPLE AVERAGE " ]

.BR "action police avrate"

.IR RATE " [ " CONTROL " ]"

.ti -8

.IR CONTROL " :="

.BI conform-exceed " EXCEEDACT\fR[\fB/\fINOTEXCEEDACT"

.ti -8

.IR EXCEEDACT/NOTEXCEEDACT " := { "

.BR pipe " | " ok " | " reclassify " | " drop " | " continue " | " goto " " chain " " CHAIN_INDEX " }"

.SH DESCRIPTION

The

.B police

action allows to limit bandwidth of traffic matched by the filter it is

attached to. Basically there are two different algorithms available to measure

the packet rate: The first one uses an internal dual token bucket and is

configured using the

.BR rate ", " burst ", " mtu ", " peakrate ", " overhead " and " linklayer

parameters. The second one uses an in-kernel sampling mechanism. It can be

fine-tuned using the

.B estimator

filter parameter.

.SH OPTIONS

.TP

.BI rate " RATE"

The maximum traffic rate of packets passing this action. Those exceeding it will

be treated as defined by the

.B conform-exceed

option.

.TP

.BI burst " BYTES\fR[\fB/\fIBYTES\fR]"

Set the maximum allowed burst in bytes, optionally followed by a slash ('/')

sign and cell size which must be a power of 2.

.TP

.BI mtu " BYTES\fR[\fB/\fIBYTES\fR]"

This is the maximum packet size handled by the policer (larger ones will be

handled like they exceeded the configured rate). Setting this value correctly

will improve the scheduler's precision.

Value formatting is identical to

.B burst

above. Defaults to unlimited.

.TP

.BI peakrate " RATE"

Set the maximum bucket depletion rate, exceeding

.BR rate .

.TP

.BI avrate " RATE"

Make use of an in-kernel bandwidth rate estimator and match the given

.I RATE

against it.

.TP

.BI overhead " BYTES"

Account for protocol overhead of encapsulating output devices when computing

.BR rate " and " peakrate .

.TP

.BI linklayer " TYPE"

Specify the link layer type.

.I TYPE

may be one of

.B ethernet

(the default),

.BR atm " or " adsl

(which are synonyms). It is used to align the precomputed rate tables to ATM

cell sizes, for

.B ethernet

no action is taken.

.TP

.BI estimator " SAMPLE AVERAGE"

Fine-tune the in-kernel packet rate estimator.

.IR SAMPLE " and " AVERAGE

are time values and control the frequency in which samples are taken and over

what timespan an average is built.

.TP

.BI conform-exceed " EXCEEDACT\fR[\fB/\fINOTEXCEEDACT\fR]"

Define how to handle packets which exceed or conform the

configured bandwidth limit. Possible values are:

.RS

.IP continue

Don't do anything, just continue with the next action in line.

.IP drop

Drop the packet immediately.

.IP shot

This is a synonym to

.BR drop .

.IP ok

Accept the packet. This is the default for conforming packets.

.IP pass

This is a synonym to

.BR ok .

.IP reclassify

Treat the packet as non-matching to the filter this action is attached to and

continue with the next filter in line (if any). This is the default for

exceeding packets.

.IP pipe

Pass the packet to the next action in line.

.RE

.SH EXAMPLES

A typical application of the police action is to enforce ingress traffic rate

by dropping exceeding packets. Although better done on the sender's side,

especially in scenarios with lack of peer control (e.g. with dial-up providers)

this is often the best one can do in order to keep latencies low under high

load. The following establishes input bandwidth policing to 1mbit/s using the

.B ingress

qdisc and

.B u32

filter:

.RS

.EX

# tc qdisc add dev eth0 handle ffff: ingress

# tc filter add dev eth0 parent ffff: u32 \\

	match u32 0 0 \\

	police rate 1mbit burst 100k

.EE

.RE

As an action can not live on it's own, there always has to be a filter involved as link between qdisc and action. The example above uses

.B u32

for that, which is configured to effectively match any packet (passing it to the

.B police

action thereby).

.SH SEE ALSO

.BR tc (8)