tc(8) — Linux manual page

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

TC(8)                             Linux                            TC(8)

NAME         top

       tc - show / manipulate traffic control settings

SYNOPSIS         top

       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 ] 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] ] }

        FORMAT := { -s[tatistics] | -d[etails] | -r[aw] | -i[ec] |
       -g[raph] | -j[json] | -p[retty] | -col[or] }

DESCRIPTION         top

       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.

QDISCS         top

       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.

CLASSES         top

       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.

FILTERS         top

       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.

QEVENTS         top

       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

CLASSLESS QDISCS         top

       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 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.

CONFIGURING CLASSLESS QDISCS         top

       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.

CLASSFUL QDISCS         top

       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.

       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.

THEORY OF OPERATION         top

       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 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.

NAMING         top

       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.

PARAMETERS         top

       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.

TC COMMANDS         top

       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.

MONITOR         top

       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.

OPTIONS         top

       -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>]

FORMAT         top

       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.

EXAMPLES         top

       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.

HISTORY         top

       tc was written by Alexey N. Kuznetsov and added in Linux 2.2.

SEE ALSO         top

       tc-basic(8), tc-bfifo(8), tc-bpf(8), tc-cake(8), tc-cbq(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-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-tcindex(8), tc-u32(8),
       User documentation at http://lartc.org/ , but please direct
       bugreports and patches to: <netdev@vger.kernel.org>

AUTHOR         top

       Manpage maintained by bert hubert (ahu@ds9a.nl)

COLOPHON         top

       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
       ⟨https://git.kernel.org/pub/scm/network/iproute2/iproute2.git⟩ on
       2020-12-18.  (At that time, the date of the most recent commit
       that was found in the repository was 2020-12-15.)  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)

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