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

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 ] 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 ] [ FORMAT ] qdisc show [ dev DEV ]

       tc [ OPTIONS ] [ FORMAT ] class show dev DEV

       tc [ OPTIONS ] filter show dev DEV

        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] }

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.

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.

       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.

       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 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.

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 a unit (both SI and IEC units
              supported).

              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.

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.

       -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).

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
              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.

       -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-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>

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 
       ⟨git://git.kernel.org/pub/scm/linux/kernel/git/shemminger/iproute2.git⟩
       on 2017-03-13.  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)