.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)