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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 ] [ ingress_block BLOCK_INDEX ] [  egress_block  BLOCK_INDEX  ]
       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 spe-
       cific parameters ] flowid flow-id

       tc [ OPTIONS ] filter [ add | change | replace | delete | get ] block BLOCK_INDEX [ handle
       filter-id  ] protocol protocol prio priority filtertype [ filtertype specific parameters ]
       flowid flow-id

       tc [ OPTIONS ] chain [ add | delete | get ] dev DEV [ parent qdisc-id | root ]  filtertype
       [ filtertype specific parameters ]

       tc [ OPTIONS ] chain [ add | delete | get ] block BLOCK_INDEX filtertype [ filtertype spe-
       cific parameters ]

       tc [ OPTIONS ] [ FORMAT ] qdisc { show | list } [ dev DEV ] [  root  |  ingress  |  handle
       QHANDLE | parent CLASSID ] [ invisible ]

       tc [ OPTIONS ] [ FORMAT ] class show dev DEV

       tc [ OPTIONS ] filter show dev DEV

       tc [ OPTIONS ] filter show block BLOCK_INDEX

       tc [ OPTIONS ] chain show dev DEV

       tc [ OPTIONS ] chain show block BLOCK_INDEX

       tc [ OPTIONS ] monitor [ file FILENAME ]

        OPTIONS  :=  {  [ -force ] -b[atch] [ filename ] | [ -n[etns] name ] | [ -N[umeric] ] | [
       -nm | -nam[es] ] | [ { -cf | -c[onf] } [ filename ] ] [ -t[imestamp] ] | [ -t[short]  |  [
       -o[neline] ] }

        FORMAT  :=  {  -s[tatistics]  |  -d[etails]  |  -r[aw]  |  -i[ec] | -g[raph] | -j[json] |
       -p[retty] | -col[or] }

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 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. Re-
              ordering 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 fil-
       ters.

QDISCS
       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
       Some  qdiscs  can  contain classes, which contain further qdiscs - traffic may then be en-
       queued 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
       A  filter  is  used  by  a classful qdisc to determine in which class a packet will be en-
       queued. 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 at-
       tached 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 se-
              lectable 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.

QEVENTS
       Qdiscs  may  invoke  user-configured actions when certain interesting events take place in
       the qdisc. Each qevent can either be unused, or can have a block attached to it.  To  this
       block  are  then attached filters using the "tc block BLOCK_IDX" syntax. The block is exe-
       cuted when the qevent associated with the  attachment  point  takes  place.  For  example,
       packet  could be dropped, or delayed, etc., depending on the qdisc and the qevent in ques-
       tion.

       For example:

              tc qdisc add dev eth0 root handle 1: red limit 500K avpkt 1K \
                 qevent early_drop block 10
              tc filter add block 10 matchall action mirred egress mirror dev eth1

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 identify and penalize flows that mo-
              nopolize 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 algo-
              rithm (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  disci-
              pline.  Reordering  within  a  flow  is  avoided since Codel internally uses a FIFO
              queue.

       fq_pie FQ-PIE (Flow Queuing with Proportional Integral controller Enhanced) is  a  queuing
              discipline  that combines Flow Queuing with the PIE AQM scheme. FQ-PIE uses a Jenk-
              ins hash function to classify incoming packets into different flows and is used  to
              provide  a  fair share of the bandwidth to all the flows using the qdisc. Each such
              flow is managed by the PIE algorithm.

       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-hit-
              ters. 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 al-
              low to add delay, packet loss, duplication and more other characteristics to  pack-
              ets 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  as-
              signed 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 config-
              ured 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 configured 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 con-
              tains 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  use-
              ful 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 classifi-
              cation.

       ETS    The  ETS  qdisc  is  a queuing discipline that merges functionality of PRIO and DRR
              qdiscs in one scheduler. ETS makes it easy to configure a set of strict  and  band-
              width-sharing bands to implement the transmission selection described in 802.1Qaz.

       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 band-
              width  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
       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,  al-
       though  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 in-
              structions. Filters can match on all fields of a packet header, as well as  on  the
              firewall mark applied by 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  automati-
       cally 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  ex-
              pected to have children.

       CLASSES
              Classes residing under a qdisc share their qdisc major number, but each have a sep-
              arate 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 hier-
              archy.

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 either a unit (both SI and IEC units supported), or a float followed by
              a '%' character to specify the rate as a percentage of the device's speed (e.g. 5%,
              99.5%). Warning: specifying the rate as a percentage means a fraction of  the  cur-
              rent speed; if the speed changes, the value will not be recalculated.

              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 op-
              tional 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 de-
              fault, but you can indicate TC to interpret them as octal and hexadecimal by adding
              a '0' or '0x' prefix respectively.

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 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 sub-
              classes and their leaf qdiscs are automatically deleted, as well as any filters at-
              tached to them.

       change Some entities can be modified 'in place'. Shares the syntax of 'add', with the  ex-
              ception  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.

MONITOR
       The tc utility  can monitor events generated by the kernel such as adding/deleting qdiscs,
       filters or actions, or modifying existing ones.

       The following command is available for monitor :

       file   If the file option is given, the tc does not listen to kernel events, but opens the
              given  file and dumps its contents. The file has to be in binary format and contain
              netlink messages.

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 execu-
              tion of the commands, the application return code will be non zero.

       -o, -oneline
              output each record on a single line, replacing line feeds with the  '\'  character.
              This is convenient when you want to count records with wc(1) or to grep(1) the out-
              put.

       -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 }

       -N, -Numeric
              Print the number of protocol, scope, dsfield, etc directly instead of converting it
              to human readable name.

       -cf, -conf <FILENAME>
              specifies path to the config file. This option is used in  conjunction  with  other
              options (e.g.  -nm).

       -t, -timestamp
              When tc monitor runs, print timestamp before the event message in format:
                 Timestamp: <Day> <Month> <DD> <hh:mm:ss> <YYYY> <usecs> usec

       -ts, -tshort
              When tc monitor runs, prints short timestamp before the event message in format:
                 [<YYYY>-<MM>-<DD>T<hh:mm:ss>.<ms>]

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
              for  u32  filter, decode offset and mask values to equivalent filter commands based
              on TCP/IP.  In JSON output, add whitespace to improve readability.

       -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  op-
              tion was specified. Classes can be filtered only by dev option.

       -c[color][={always|auto|never}
              Configure  color output. If parameter is omitted or always, color output is enabled
              regardless of stdout state. If parameter is auto, stdout is checked to be a  termi-
              nal  before enabling color output. If parameter is never, color output is disabled.
              If specified multiple times, the last one takes precedence. This flag is ignored if
              -json is also given.

       -j, -json
              Display results in JSON format.

       -nm, -name
              resolve class name from /etc/iproute2/tc_cls file or from file specified by -cf op-
              tion. 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.

       -br, -brief
              Print only essential data needed to identify the filter and action (handle, cookie,
              etc.)  and  stats. This option is currently only supported by tc filter show and tc
              actions ls commands.

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-cake(8), tc-cbq(8), tc-cgroup(8), tc-choke(8), tc-
       codel(8),  tc-drr(8),  tc-ematch(8),  tc-ets(8),  tc-flow(8),  tc-flower(8), tc-fq(8), tc-
       fq_codel(8), tc-fq_pie(8), tc-fw(8), tc-hfsc(7), tc-hfsc(8), tc-htb(8), tc-mqprio(8),  tc-
       pfifo(8),  tc-pfifo_fast(8),  tc-pie(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 AT vger.org>

AUTHOR
       Manpage maintained by bert hubert (ahu AT ds9a.nl)

iproute2                                 16 December 2001                                   TC(8)

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