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           tc  qdisc [ add | change | replace | link ] dev DEV [ parent qdisc-id |
           root ] [ handle qdisc-id ] qdisc [ qdisc specific parameters ]
           tc class [ add | change | replace ] dev DEV parent qdisc-id  [  classid
           class-id ] qdisc [ qdisc specific parameters ]
           tc filter [ add | change | replace ] dev DEV [ parent qdisc-id | root ]
           protocol protocol prio priority filtertype [ filtertype specific param-
           eters ] flowid flow-id
           tc [ FORMAT ] qdisc show [ dev DEV ]
           tc [ FORMAT ] class show dev DEV
           tc filter show dev DEV
           tc [ -force ] [ -OK ] -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.
                  Where shaping deals with transmission of traffic, policing  per-
                  tains 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:
                  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  though  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
           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.


           All  parameters  accept a floating point number, possibly followed by a
           Bandwidths or rates can be specified in:
           kbps   Kilobytes per second
           mbps   Megabytes per second
           kbit   Kilobits per second
           mbit   Megabits per second
           bps or a bare number
                  Bytes per second
           Amounts of data can be specified in:
           kb or k
           mb or m
           mbit   Megabits
           kbit   Kilobits
           b or a bare number
           Lengths of time can be specified in:
                  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.
           remove A qdisc can be removed 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.


           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


           tc-cbq(8), tc-htb(8), tc-sfq(8), tc-red(8), tc-tbf(8), tc-pfifo(8), tc-
           bfifo(8), tc-pfifo_fast(8),
           User documentation at, but please  direct  bugreports
           and patches to: <>


           Manpage maintained by bert hubert (

    iproute2 16 December 2001 TC(8)


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