tc - show / manipulate traffic control settings


   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  ]  dev  DEV  [
   parent  qdisc-id  | root ] 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] }


   Tc is used to configure Traffic Control in the  Linux  kernel.  Traffic
   Control consists of the following:

          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.

          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.

          Whereas  shaping  deals  with  transmission of traffic, policing
          pertains to traffic arriving. Policing thus occurs on ingress.

          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

   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

   rsvp   Match Resource Reservation Protocol (RSVP) packets.

          Filter packets based on traffic control index. See tc-index(8).

   u32    Generic  filtering  on arbitrary packet data, assisted by syntax
          to abstract common operations. See tc-u32(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.

          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.

          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.

          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.

          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

   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

   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

   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.

          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 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  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 a  unit  (both  SI  and  IEC  units

          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

          us, usec, usecs or a bare number

          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

          kbit   Kilobits

          kb or k

          mbit   Megabits

          mb or m

          gbit   Gigabits

          gb or g

          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


   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

          Performs a nearly atomic remove/add on an existing node  id.  If
          the node does not exist yet it is created.

   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 }


          tc -n[etns] NETNS [ OPTIONS ] OBJECT { COMMAND | help }

   -cf, -conf <FILENAME>
          specifies path to the  config  file.  This  option  is  used  in
          conjuction 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.

   -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),
   User  documentation  at, but please direct bugreports
   and patches to: <>


   Manpage maintained by bert hubert (


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