Policing action in tc(8) Linux Policing action in tc(8)
NAME
police - policing action
SYNOPSIS
tc ... action police [ rate RATE burst BYTES[/BYTES] ] [ pkts_rate RATE
pkts_burst PACKETS] [ mtu BYTES[/BYTES] ] [ peakrate RATE ] [
overhead BYTES ] [ linklayer TYPE ] [ CONTROL ]
tc ... filter ... [ estimator SAMPLE AVERAGE ] action police avrate
RATE [ CONTROL ]
CONTROL := conform-exceed EXCEEDACT[/NOTEXCEEDACT
EXCEEDACT/NOTEXCEEDACT := { pipe | ok | reclassify | drop | continue |
goto chain CHAIN_INDEX }
DESCRIPTION
The police action allows limiting of the byte or packet rate of traffic
matched by the filter it is attached to.
There are two different algorithms available to measure the byte rate:
The first one uses an internal dual token bucket and is configured us-
ing the rate, burst, mtu, peakrate, overhead and linklayer parameters.
The second one uses an in-kernel sampling mechanism. It can be fine-
tuned using the estimator filter parameter.
There is one algorithm available to measure packet rate and it is simi-
lar to the first algorithm described for byte rate. It is configured
using the pkt_rate and pkt_burst parameters.
At least one of the rate and pkt_rate parameters must be configured.
OPTIONS
rate RATE
The maximum byte rate of packets passing this action. Those ex-
ceeding it will be treated as defined by the conform-exceed op-
tion.
burst BYTES[/BYTES]
Set the maximum allowed burst in bytes, optionally followed by a
slash ('/') sign and cell size which must be a power of 2.
pkt_rate RATE
The maximum packet rate or packets passing this action. Those
exceeding it will be treated as defined by the conform-exceed
option.
pkt_burst PACKETS
Set the maximum allowed burst in packets.
mtu BYTES[/BYTES]
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 preci-
sion. Value formatting is identical to burst above. Defaults to
unlimited.
peakrate RATE
Set the maximum bucket depletion rate, exceeding rate.
avrate RATE
Make use of an in-kernel bandwidth rate estimator and match the
given RATE against it.
overhead BYTES
Account for protocol overhead of encapsulating output devices
when computing rate and peakrate.
linklayer TYPE
Specify the link layer type. TYPE may be one of ethernet (the
default), atm or adsl (which are synonyms). It is used to align
the precomputed rate tables to ATM cell sizes, for ethernet no
action is taken.
estimator SAMPLE AVERAGE
Fine-tune the in-kernel packet rate estimator. SAMPLE and AVER-
AGE are time values and control the frequency in which samples
are taken and over what timespan an average is built.
conform-exceed EXCEEDACT[/NOTEXCEEDACT]
Define how to handle packets which exceed or conform the config-
ured bandwidth limit. Possible values are:
continue
Don't do anything, just continue with the next action in
line.
drop Drop the packet immediately.
shot This is a synonym to drop.
ok Accept the packet. This is the default for conforming
packets.
pass This is a synonym to ok.
reclassify
Treat the packet as non-matching to the filter this ac-
tion is attached to and continue with the next filter in
line (if any). This is the default for exceeding packets.
pipe Pass the packet to the next action in line.
EXAMPLES
A typical application of the police action is to enforce ingress traf-
fic 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 ingress qdisc and u32 filter:
# 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
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 u32
for that, which is configured to effectively match any packet (passing
it to the police action thereby).
SEE ALSO
tc(8)
iproute2 20 Jan 2015 Policing action in tc(8)
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