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NAME | SYNOPSIS | DESCRIPTION | QDISCS | CLASSES | FILTERS | QEVENTS | CLASSLESS QDISCS | CONFIGURING CLASSLESS QDISCS | CLASSFUL QDISCS | THEORY OF OPERATION | NAMING | PARAMETERS | TC COMMANDS | MONITOR | OPTIONS | FORMAT | EXAMPLES | HISTORY | SEE ALSO | AUTHOR | COLOPHON |
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TC(8) Linux TC(8)
tc - show / manipulate traffic control settings
tc [ OPTIONS ] qdisc [ add | change | replace | link | delete ]
dev DEV [ parent qdisc-id | root ] [ handle qdisc-id ] [
ingress_block BLOCK_INDEX ] [ egress_block BLOCK_INDEX ] qdisc [
qdisc specific parameters ]
tc [ OPTIONS ] class [ add | change | replace | delete | show ]
dev DEV parent qdisc-id [ classid class-id ] qdisc [ qdisc
specific parameters ]
tc [ OPTIONS ] filter [ add | change | replace | delete | get ]
dev DEV [ parent qdisc-id | root ] [ handle filter-id ] protocol
protocol prio priority filtertype [ filtertype specific
parameters ] flowid flow-id
tc [ OPTIONS ] filter [ add | change | replace | delete | get ]
block BLOCK_INDEX [ handle filter-id ] protocol protocol prio
priority filtertype [ filtertype specific parameters ] flowid
flow-id
tc [ OPTIONS ] chain [ add | delete | get ] dev DEV [ parent
qdisc-id | root ] filtertype [ filtertype specific parameters ]
tc [ OPTIONS ] chain [ add | delete | get ] block BLOCK_INDEX
filtertype [ filtertype specific parameters ]
tc [ OPTIONS ] [ FORMAT ] qdisc { show | list } [ dev DEV ] [
root | ingress | handle QHANDLE | parent CLASSID ] [ invisible ]
tc [ OPTIONS ] [ FORMAT ] class show dev DEV
tc [ OPTIONS ] filter show dev DEV
tc [ OPTIONS ] filter show block BLOCK_INDEX
tc [ OPTIONS ] chain show dev DEV
tc [ OPTIONS ] chain show block BLOCK_INDEX
tc [ OPTIONS ] monitor [ file FILENAME ]
OPTIONS := { [ -force ] -b[atch] [ filename ] | [ -n[etns] name
] | [ -N[umeric] ] | [ -nm | -nam[es] ] | [ { -cf | -c[onf] } [
filename ] ] [ -t[imestamp] ] | [ -t[short] | [ -o[neline] ] | [
-echo ] }
FORMAT := { -s[tatistics] | -d[etails] | -r[aw] | -i[ec] |
-g[raph] | -j[json] | -p[retty] | -col[or] }
Tc is used to configure Traffic Control in the Linux kernel.
Traffic Control consists of the following:
SHAPING
When traffic is shaped, its rate of transmission is under
control. Shaping may be more than lowering the available
bandwidth - it is also used to smooth out bursts in
traffic for better network behaviour. Shaping occurs on
egress.
SCHEDULING
By scheduling the transmission of packets it is possible
to improve interactivity for traffic that needs it while
still guaranteeing bandwidth to bulk transfers. Reordering
is also called prioritizing, and happens only on egress.
POLICING
Whereas shaping deals with transmission of traffic,
policing pertains to traffic arriving. Policing thus
occurs on ingress.
DROPPING
Traffic exceeding a set bandwidth may also be dropped
forthwith, both on ingress and on egress.
Processing of traffic is controlled by three kinds of objects:
qdiscs, classes and filters.
qdisc is short for 'queueing discipline' and it is elementary to
understanding traffic control. Whenever the kernel needs to send
a packet to an interface, it is enqueued to the qdisc configured
for that interface. Immediately afterwards, the kernel tries to
get as many packets as possible from the qdisc, for giving them
to the network adaptor driver.
A simple QDISC is the 'pfifo' one, which does no processing at
all and is a pure First In, First Out queue. It does however
store traffic when the network interface can't handle it
momentarily.
Some qdiscs can contain classes, which contain further qdiscs -
traffic may then be enqueued in any of the inner qdiscs, which
are within the classes. When the kernel tries to dequeue a
packet from such a classful qdisc it can come from any of the
classes. A qdisc may for example prioritize certain kinds of
traffic by trying to dequeue from certain classes before others.
A filter is used by a classful qdisc to determine in which class
a packet will be enqueued. Whenever traffic arrives at a class
with subclasses, it needs to be classified. Various methods may
be employed to do so, one of these are the filters. All filters
attached to the class are called, until one of them returns with
a verdict. If no verdict was made, other criteria may be
available. This differs per qdisc.
It is important to notice that filters reside within qdiscs -
they are not masters of what happens.
The available filters are:
basic Filter packets based on an ematch expression. See
tc-ematch(8) for details.
bpf Filter packets using (e)BPF, see tc-bpf(8) for details.
cgroup Filter packets based on the control group of their
process. See tc-cgroup(8) for details.
flow, flower
Flow-based classifiers, filtering packets based on their
flow (identified by selectable keys). See tc-flow(8) and
tc-flower(8) for details.
fw Filter based on fwmark. Directly maps fwmark value to
traffic class. See tc-fw(8).
route Filter packets based on routing table. See tc-route(8) for
details.
u32 Generic filtering on arbitrary packet data, assisted by
syntax to abstract common operations. See tc-u32(8) for
details.
matchall
Traffic control filter that matches every packet. See
tc-matchall(8) for details.
Qdiscs may invoke user-configured actions when certain
interesting events take place in the qdisc. Each qevent can
either be unused, or can have a block attached to it. To this
block are then attached filters using the "tc block BLOCK_IDX"
syntax. The block is executed when the qevent associated with the
attachment point takes place. For example, packet could be
dropped, or delayed, etc., depending on the qdisc and the qevent
in question.
For example:
tc qdisc add dev eth0 root handle 1: red limit 500K avpkt
1K \
qevent early_drop block 10
tc filter add block 10 matchall action mirred egress
mirror dev eth1
The classless qdiscs are:
choke CHOKe (CHOose and Keep for responsive flows, CHOose and
Kill for unresponsive flows) is a classless qdisc designed
to both identify and penalize flows that monopolize the
queue. CHOKe is a variation of RED, and the configuration
is similar to RED.
codel CoDel (pronounced "coddle") is an adaptive "no-knobs"
active queue management algorithm (AQM) scheme that was
developed to address the shortcomings of RED and its
variants.
[p|b]fifo
Simplest usable qdisc, pure First In, First Out behaviour.
Limited in packets or in bytes.
fq Fair Queue Scheduler realises TCP pacing and scales to
millions of concurrent flows per qdisc.
fq_codel
Fair Queuing Controlled Delay is queuing discipline that
combines Fair Queuing with the CoDel AQM scheme. FQ_Codel
uses a stochastic model to classify incoming packets into
different flows and is used to provide a fair share of the
bandwidth to all the flows using the queue. Each such flow
is managed by the CoDel queuing discipline. Reordering
within a flow is avoided since Codel internally uses a
FIFO queue.
fq_pie FQ-PIE (Flow Queuing with Proportional Integral controller
Enhanced) is a queuing discipline that combines Flow
Queuing with the PIE AQM scheme. FQ-PIE uses a Jenkins
hash function to classify incoming packets into different
flows and is used to provide a fair share of the bandwidth
to all the flows using the qdisc. Each such flow is
managed by the PIE algorithm.
gred Generalized Random Early Detection combines multiple RED
queues in order to achieve multiple drop priorities. This
is required to realize Assured Forwarding (RFC 2597).
hhf Heavy-Hitter Filter differentiates between small flows and
the opposite, heavy-hitters. The goal is to catch the
heavy-hitters and move them to a separate queue with less
priority so that bulk traffic does not affect the latency
of critical traffic.
ingress
This is a special qdisc as it applies to incoming traffic
on an interface, allowing for it to be filtered and
policed.
mqprio The Multiqueue Priority Qdisc is a simple queuing
discipline that allows mapping traffic flows to hardware
queue ranges using priorities and a configurable priority
to traffic class mapping. A traffic class in this context
is a set of contiguous qdisc classes which map 1:1 to a
set of hardware exposed queues.
multiq Multiqueue is a qdisc optimized for devices with multiple
Tx queues. It has been added for hardware that wishes to
avoid head-of-line blocking. It will cycle though the
bands and verify that the hardware queue associated with
the band is not stopped prior to dequeuing a packet.
netem Network Emulator is an enhancement of the Linux traffic
control facilities that allow one to add delay, packet
loss, duplication and more other characteristics to
packets outgoing from a selected network interface.
pfifo_fast
Standard qdisc for 'Advanced Router' enabled kernels.
Consists of a three-band queue which honors Type of
Service flags, as well as the priority that may be
assigned to a packet.
pie Proportional Integral controller-Enhanced (PIE) is a
control theoretic active queue management scheme. It is
based on the proportional integral controller but aims to
control delay.
red Random Early Detection simulates physical congestion by
randomly dropping packets when nearing configured
bandwidth allocation. Well suited to very large bandwidth
applications.
sfb Stochastic Fair Blue is a classless qdisc to manage
congestion based on packet loss and link utilization
history while trying to prevent non-responsive flows (i.e.
flows that do not react to congestion marking or dropped
packets) from impacting performance of responsive flows.
Unlike RED, where the marking probability has to be
configured, BLUE tries to determine the ideal marking
probability automatically.
sfq Stochastic Fairness Queueing reorders queued traffic so
each 'session' gets to send a packet in turn.
tbf The Token Bucket Filter is suited for slowing traffic down
to a precisely configured rate. Scales well to large
bandwidths.
In the absence of classful qdiscs, classless qdiscs can only be
attached at the root of a device. Full syntax:
tc qdisc add dev DEV root QDISC QDISC-PARAMETERS
To remove, issue
tc qdisc del dev DEV root
The pfifo_fast qdisc is the automatic default in the absence of a
configured qdisc.
The classful qdiscs are:
ATM Map flows to virtual circuits of an underlying
asynchronous transfer mode device.
DRR The Deficit Round Robin Scheduler is a more flexible
replacement for Stochastic Fairness Queuing. Unlike SFQ,
there are no built-in queues -- you need to add classes
and then set up filters to classify packets accordingly.
This can be useful e.g. for using RED qdiscs with
different settings for particular traffic. There is no
default class -- if a packet cannot be classified, it is
dropped.
ETS The ETS qdisc is a queuing discipline that merges
functionality of PRIO and DRR qdiscs in one scheduler. ETS
makes it easy to configure a set of strict and bandwidth-
sharing bands to implement the transmission selection
described in 802.1Qaz.
HFSC Hierarchical Fair Service Curve guarantees precise
bandwidth and delay allocation for leaf classes and
allocates excess bandwidth fairly. Unlike HTB, it makes
use of packet dropping to achieve low delays which
interactive sessions benefit from.
HTB The Hierarchy Token Bucket implements a rich linksharing
hierarchy of classes with an emphasis on conforming to
existing practices. HTB facilitates guaranteeing bandwidth
to classes, while also allowing specification of upper
limits to inter-class sharing. It contains shaping
elements, based on TBF and can prioritize classes.
PRIO The PRIO qdisc is a non-shaping container for a
configurable number of classes which are dequeued in
order. This allows for easy prioritization of traffic,
where lower classes are only able to send if higher ones
have no packets available. To facilitate configuration,
Type Of Service bits are honored by default.
QFQ Quick Fair Queueing is an O(1) scheduler that provides
near-optimal guarantees, and is the first to achieve that
goal with a constant cost also with respect to the number
of groups and the packet length. The QFQ algorithm has no
loops, and uses very simple instructions and data
structures that lend themselves very well to a hardware
implementation.
Classes form a tree, where each class has a single parent. A
class may have multiple children. Some qdiscs allow for runtime
addition of classes (HTB) while others (PRIO) are created with a
static number of children.
Qdiscs which allow dynamic addition of classes can have zero or
more subclasses to which traffic may be enqueued.
Furthermore, each class contains a leaf qdisc which by default
has pfifo behaviour, although another qdisc can be attached in
place. This qdisc may again contain classes, but each class can
have only one leaf qdisc.
When a packet enters a classful qdisc it can be classified to one
of the classes within. Three criteria are available, although not
all qdiscs will use all three:
tc filters
If tc filters are attached to a class, they are consulted
first for relevant instructions. Filters can match on all
fields of a packet header, as well as on the firewall mark
applied by iptables.
Type of Service
Some qdiscs have built in rules for classifying packets
based on the TOS field.
skb->priority
Userspace programs can encode a class-id in the
'skb->priority' field using the SO_PRIORITY option.
Each node within the tree can have its own filters but higher
level filters may also point directly to lower classes.
If classification did not succeed, packets are enqueued to the
leaf qdisc attached to that class. Check qdisc specific manpages
for details, however.
All qdiscs, classes and filters have IDs, which can either be
specified or be automatically assigned.
IDs consist of a major number and a minor number, separated by a
colon - major:minor. Both major and minor are hexadecimal
numbers and are limited to 16 bits. There are two special values:
root is signified by major and minor of all ones, and unspecified
is all zeros.
QDISCS A qdisc, which potentially can have children, gets
assigned a major number, called a 'handle', leaving the
minor number namespace available for classes. The handle
is expressed as '10:'. It is customary to explicitly
assign a handle to qdiscs expected to have children.
CLASSES
Classes residing under a qdisc share their qdisc major
number, but each have a separate minor number called a
'classid' that has no relation to their parent classes,
only to their parent qdisc. The same naming custom as for
qdiscs applies.
FILTERS
Filters have a three part ID, which is only needed when
using a hashed filter hierarchy.
The following parameters are widely used in TC. For other
parameters, see the man pages for individual qdiscs.
RATES Bandwidths or rates. These parameters accept a floating
point number, possibly followed by either a unit (both SI
and IEC units supported), or a float followed by a '%'
character to specify the rate as a percentage of the
device's speed (e.g. 5%, 99.5%). Warning: specifying the
rate as a percentage means a fraction of the current
speed; if the speed changes, the value will not be
recalculated.
bit or a bare number
Bits per second
kbit Kilobits per second
mbit Megabits per second
gbit Gigabits per second
tbit Terabits per second
bps Bytes per second
kbps Kilobytes per second
mbps Megabytes per second
gbps Gigabytes per second
tbps Terabytes per second
To specify in IEC units, replace the SI prefix (k-, m-,
g-, t-) with IEC prefix (ki-, mi-, gi- and ti-)
respectively.
TC store rates as a 32-bit unsigned integer in bps
internally, so we can specify a max rate of 4294967295
bps.
TIMES Length of time. Can be specified as a floating point
number followed by an optional unit:
s, sec or secs
Whole seconds
ms, msec or msecs
Milliseconds
us, usec, usecs or a bare number
Microseconds.
TC defined its own time unit (equal to microsecond) and
stores time values as 32-bit unsigned integer, thus we can
specify a max time value of 4294967295 usecs.
SIZES Amounts of data. Can be specified as a floating point
number followed by an optional unit:
b or a bare number
Bytes.
kbit Kilobits
kb or k
Kilobytes
mbit Megabits
mb or m
Megabytes
gbit Gigabits
gb or g
Gigabytes
TC stores sizes internally as 32-bit unsigned integer in
byte, so we can specify a max size of 4294967295 bytes.
VALUES Other values without a unit. These parameters are
interpreted as decimal by default, but you can indicate TC
to interpret them as octal and hexadecimal by adding a '0'
or '0x' prefix respectively.
The following commands are available for qdiscs, classes and
filter:
add Add a qdisc, class or filter to a node. For all entities,
a parent must be passed, either by passing its ID or by
attaching directly to the root of a device. When creating
a qdisc or a filter, it can be named with the handle
parameter. A class is named with the classid parameter.
delete A qdisc can be deleted by specifying its handle, which may
also be 'root'. All subclasses and their leaf qdiscs are
automatically deleted, as well as any filters attached to
them.
change Some entities can be modified 'in place'. Shares the
syntax of 'add', with the exception that the handle cannot
be changed and neither can the parent. In other words,
change cannot move a node.
replace
Performs a nearly atomic remove/add on an existing node
id. If the node does not exist yet it is created.
get Displays a single filter given the interface DEV, qdisc-
id, priority, protocol and filter-id.
show Displays all filters attached to the given interface. A
valid parent ID must be passed.
link Only available for qdiscs and performs a replace where the
node must exist already.
The tc utility can monitor events generated by the kernel such as
adding/deleting qdiscs, filters or actions, or modifying existing
ones.
The following command is available for monitor :
file If the file option is given, the tc does not listen to
kernel events, but opens the given file and dumps its
contents. The file has to be in binary format and contain
netlink messages.
-b, -b filename, -batch, -batch filename
read commands from provided file or standard input and
invoke them. First failure will cause termination of tc.
-force don't terminate tc on errors in batch mode. If there were
any errors during execution of the commands, the
application return code will be non zero.
-o, -oneline
output each record on a single line, replacing line feeds
with the '\' character. This is convenient when you want
to count records with wc(1) or to grep(1) the output.
-n, -net, -netns <NETNS>
switches tc to the specified network namespace NETNS.
Actually it just simplifies executing of:
ip netns exec NETNS tc [ OPTIONS ] OBJECT { COMMAND | help
}
to
tc -n[etns] NETNS [ OPTIONS ] OBJECT { COMMAND | help }
-N, -Numeric
Print the number of protocol, scope, dsfield, etc directly
instead of converting it to human readable name.
-cf, -conf <FILENAME>
specifies path to the config file. This option is used in
conjunction with other options (e.g. -nm).
-t, -timestamp
When tc monitor runs, print timestamp before the event
message in format:
Timestamp: <Day> <Month> <DD> <hh:mm:ss> <YYYY> <usecs>
usec
-ts, -tshort
When tc monitor runs, prints short timestamp before the
event message in format:
[<YYYY>-<MM>-<DD>T<hh:mm:ss>.<ms>]
-echo Request the kernel to send the applied configuration back.
The show command has additional formatting options:
-s, -stats, -statistics
output more statistics about packet usage.
-d, -details
output more detailed information about rates and cell
sizes.
-r, -raw
output raw hex values for handles.
-p, -pretty
for u32 filter, decode offset and mask values to
equivalent filter commands based on TCP/IP. In JSON
output, add whitespace to improve readability.
-iec print rates in IEC units (ie. 1K = 1024).
-g, -graph
shows classes as ASCII graph. Prints generic stats info
under each class if -s option was specified. Classes can
be filtered only by dev option.
-c[color][={always|auto|never}
Configure color output. If parameter is omitted or always,
color output is enabled regardless of stdout state. If
parameter is auto, stdout is checked to be a terminal
before enabling color output. If parameter is never, color
output is disabled. If specified multiple times, the last
one takes precedence. This flag is ignored if -json is
also given.
-j, -json
Display results in JSON format.
-nm, -name
resolve class name from /etc/iproute2/tc_cls file or from
file specified by -cf option. This file is just a mapping
of classid to class name:
# Here is comment
1:40 voip # Here is another comment
1:50 web
1:60 ftp
1:2 home
tc will not fail if -nm was specified without -cf option
but /etc/iproute2/tc_cls file does not exist, which makes
it possible to pass -nm option for creating tc alias.
-br, -brief
Print only essential data needed to identify the filter
and action (handle, cookie, etc.) and stats. This option
is currently only supported by tc filter show and tc
actions ls commands.
tc -g class show dev eth0
Shows classes as ASCII graph on eth0 interface.
tc -g -s class show dev eth0
Shows classes as ASCII graph with stats info under each
class.
tc was written by Alexey N. Kuznetsov and added in Linux 2.2.
tc-basic(8), tc-bfifo(8), tc-bpf(8), tc-cake(8), tc-cgroup(8),
tc-choke(8), tc-codel(8), tc-drr(8), tc-ematch(8), tc-ets(8),
tc-flow(8), tc-flower(8), tc-fq(8), tc-fq_codel(8), tc-fq_pie(8),
tc-fw(8), tc-gact(8), tc-hfsc(7), tc-hfsc(8), tc-htb(8),
tc-mqprio(8), tc-pfifo(8), tc-pfifo_fast(8), tc-pie(8),
tc-red(8), tc-route(8), tc-sfb(8), tc-sfq(8), tc-stab(8),
tc-tbf(8), tc-u32(8)
User documentation at http://lartc.org/ , but please direct
bugreports and patches to: <[email protected]>
Manpage maintained by bert hubert ([email protected])
This page is part of the iproute2 (utilities for controlling
TCP/IP networking and traffic) project. Information about the
project can be found at
⟨http://www.linuxfoundation.org/collaborate/workgroups/networking/iproute2⟩.
If you have a bug report for this manual page, send it to
[email protected], [email protected]. This page was
obtained from the project's upstream Git repository
⟨https://git.kernel.org/pub/scm/network/iproute2/iproute2.git⟩ on
2024-06-14. (At that time, the date of the most recent commit
that was found in the repository was 2024-06-11.) If you
discover any rendering problems in this HTML version of the page,
or you believe there is a better or more up-to-date source for
the page, or you have corrections or improvements to the
information in this COLOPHON (which is not part of the original
manual page), send a mail to [email protected]
iproute2 16 December 2001 TC(8)
Pages that refer to this page: bpf(2), cgroups(7), tc-hfsc(7), dcb-buffer(8), dcb-maxrate(8), netsniff-ng(8), tc-actions(8), tc-basic(8), tc-bfifo(8), tc-bpf(8), tc-cake(8), tc-cgroup(8), tc-choke(8), tc-codel(8), tc-connmark(8), tc-csum(8), tc-ct(8), tc-ctinfo(8), tc-drr(8), tc-ets(8), tc-flow(8), tc-flower(8), tc-fq(8), tc-fq_codel(8), tc-fq_pie(8), tc-fw(8), tc-gact(8), tc-hfsc(8), tc-htb(8), tc-ife(8), tc-matchall(8), tc-mirred(8), tc-mpls(8), tc-nat(8), tc-netem(8), tc-pedit(8), tc-pfifo_fast(8), tc-pie(8), tc-police(8), tc-red(8), tc-route(8), tc-sample(8), tc-sfb(8), tc-sfq(8), tc-simple(8), tc-skbedit(8), tc-skbmod(8), tc-stab(8), tc-tbf(8), tc-tunnel_key(8), tc-u32(8), tc-vlan(8), trafgen(8)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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