TC(8)				     Linux				 TC(8)



NAME
       tc - show / manipulate traffic control settings

SYNOPSIS
       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] }


DESCRIPTION
       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 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.


       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
       qdisc is short for 'queueing discipline' and it is elementary to under-
       standing traffic control. Whenever the kernel needs to send a packet to
       an interface, it is enqueued to the qdisc configured  for  that	inter-
       face.  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
       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.


FILTERS
       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 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-tcin-
	      dex(8).

       u32    Generic  filtering  on arbitrary packet data, assisted by syntax
	      to abstract common operations. See tc-u32(8) for details.


CLASSLESS QDISCS
       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 iden-
	      tify 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. Lim-
	      ited 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 com-
	      bines 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 ver-
	      ify 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  perfor-
	      mance of responsive flows.  Unlike RED, where the marking proba-
	      bility 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
       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  con-
       figured qdisc.


CLASSFUL QDISCS
       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 calcula-
	      tions  based  on	average	 packet size and underlying link band-
	      width. 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 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
	      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
       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
       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 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
	      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
       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-
	      ported).

	      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 fol-
	      lowed 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  respec-
	      tively.


TC COMMANDS
       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.


       delete A	 qdisc can be deleted by specifying its handle, which may also
	      be 'root'. All subclasses and their leaf	qdiscs	are  automati-
	      cally 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.


       link   Only  available for qdiscs and performs a replace where the node
	      must exist already.


OPTIONS
       -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  con-
	      junction with other options (e.g.	 -nm).


FORMAT
       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).


       -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 possi-
	      ble to pass -nm option for creating tc alias.


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

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



iproute2		       16 December 2001				 TC(8)