tc  qdisc  [  add | change | replace | link | delete ] dev DEV [ parent
       qdisc-id | root ] [ handle qdisc-id ] qdisc [ qdisc specific parameters

       tc  class [ add | change | replace | delete ] dev DEV parent qdisc-id [
       classid class-id ] qdisc [ qdisc specific parameters ]

       tc filter [ add | change | replace | delete ] dev DEV [ parent qdisc-id
       |  root  ] protocol protocol prio priority filtertype [ filtertype spe-
       cific parameters ] flowid flow-id

       tc [ FORMAT ] qdisc show [ dev DEV ]

       tc [ FORMAT ] class show dev DEV

       tc filter show dev DEV

       tc [ -force ] -b[atch] [ filename ]

        FORMAT := { -s[tatistics] | -d[etails] | -r[aw] | -p[retty] | -i[ec] }

       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 con-
              trol. 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.

       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 class-
       ful 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 sub-
       classes, 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 classless qdiscs are:

              Simplest usable qdisc, pure First In, First Out behaviour.  Lim-
              ited in packets or in bytes.

              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.

       red    Random Early Detection simulates physical congestion by randomly
              dropping packets when nearing configured  bandwidth  allocation.
              Well suited to very large bandwidth applications.

       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

              classes.  It contains shaping elements as well  as  prioritizing
              capabilities. Shaping is performed using link idle time calcula-
              tions based on average packet size  and  underlying  link  band-
              width. The latter may be ill-defined for some interfaces.

       HTB    The Hierarchy Token Bucket implements a rich linksharing hierar-
              chy of classes with an emphasis on conforming to existing  prac-
              tices.  HTB facilitates guaranteeing bandwidth to classes, while
              also allowing specification of upper limits to inter-class shar-
              ing.  It contains shaping elements, based on TBF and can priori-
              tize 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 facil-
              itate  configuration,  Type  Of  Service  bits  are  honored  by

       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.

       unspecified is all zeros.

       QDISCS A qdisc, which potentially can have children,  gets  assigned  a
              major number, called a 'handle', leaving the minor number names-
              pace 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  sup-

              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-)

              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  respec-

       The following commands are available for qdiscs, classes and filter:

       add    Add a qdisc, class or filter to a node. For all entities, a par-
              ent 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.

              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.

       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  com-
              mands based on TCP/IP.

       -iec   print rates in IEC units (ie. 1K = 1024).

       -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.

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

       tc-bfifo(8),  tc-cbq(8),  tc-choke(8),  tc-codel(8),   tc-drr(8),   tc-
       ematch(8),   tc-fq_codel(8),  tc-hfsc(7),  tc-hfsc(8),  tc-htb(8),  tc-
       pfifo(8),  tc-pfifo_fast(8),  tc-red(8),  tc-sfb(8),   tc-sfq(8),   tc-
       stab(8), tc-tbf(8),
       User  documentation  at, but please direct bugreports
       and patches to: <>
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