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NAME | SYNOPSIS | DESCRIPTION | QDISCS | CLASSES | FILTERS | CLASSLESS QDISCS | CONFIGURING CLASSLESS QDISCS | CLASSFUL QDISCS | THEORY OF OPERATION | NAMING | PARAMETERS | TC COMMANDS | 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 ] 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 ] [ FORMAT ] qdisc show [ dev DEV ]
tc [ OPTIONS ] [ FORMAT ] class show dev DEV
tc [ OPTIONS ] filter show dev DEV
tc [ OPTIONS ] filter show block BLOCK_INDEX
OPTIONS := { [ -force ] -b[atch] [ filename ] | [ -n[etns] name ] |
[ -nm | -nam[es] ] | [ { -cf | -c[onf] } [ filename ] ] }
FORMAT := { -s[tatistics] | -d[etails] | -r[aw] | -p[retty] | -i[ec]
| -g[raph] | -j[json] }
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.
rsvp Match Resource Reservation Protocol (RSVP) packets.
tcindex
Filter packets based on traffic control index. See
tc-tcindex(8).
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.
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.
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 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.
rr Round-Robin qdisc with support for multiqueue network devices.
Removed from Linux since kernel version 2.6.27.
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.
CBQ Class Based Queueing implements a rich linksharing hierarchy
of classes. It contains shaping elements as well as
prioritizing capabilities. Shaping is performed using link
idle time calculations based on average packet size and
underlying link bandwidth. The latter may be ill-defined for
some interfaces.
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.
DSMARK Classify packets based on TOS field, change TOS field of
packets based on classification.
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 (CBQ, 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 ipchains or 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.
-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.
-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 }
-cf, -conf <FILENAME>
specifies path to the config file. This option is used in
conjunction with other options (e.g. -nm).
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
decode filter offset and mask values to equivalent filter
commands based on TCP/IP.
-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.
-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.
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-cbq(8), tc-cgroup(8),
tc-choke(8), tc-codel(8), tc-drr(8), tc-ematch(8), tc-flow(8),
tc-flower(8), tc-fq(8), tc-fq_codel(8), tc-fw(8), tc-hfsc(7),
tc-hfsc(8), tc-htb(8), tc-mqprio(8), tc-pfifo(8), tc-pfifo_fast(8),
tc-red(8), tc-route(8), tc-sfb(8), tc-sfq(8), tc-stab(8), tc-tbf(8),
tc-tcindex(8), tc-u32(8),
User documentation at http://lartc.org/ , but please direct bugreports
and patches to: <netdev@vger.kernel.org>
Manpage maintained by bert hubert (ahu@ds9a.nl)
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
netdev@vger.kernel.org, shemminger@osdl.org. This page was obtained
from the project's upstream Git repository
⟨git://git.kernel.org/pub/scm/linux/kernel/git/shemminger/iproute2.git⟩
on 2018-02-02. (At that time, the date of the most recent commit
that was found in the repository was 2018-01-29.) 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 man-pages@man7.org
iproute2 16 December 2001 TC(8)
Pages that refer to this page: bpf(2), cgroups(7), tc-hfsc(7), tc-actions(8), tc-basic(8), tc-bfifo(8), tc-bpf(8), tc-cbq(8), tc-cbq-details(8), tc-cgroup(8), tc-choke(8), tc-codel(8), tc-connmark(8), tc-csum(8), tc-drr(8), tc-flow(8), tc-flower(8), tc-fq(8), tc-fq_codel(8), tc-fw(8), tc-hfsc(8), tc-htb(8), tc-ife(8), tc-matchall(8), tc-mirred(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-tcindex(8), tc-tunnel_key(8), tc-u32(8), tc-vlan(8), tc-xt(8)
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