Provided by: iproute2_4.3.0-1ubuntu3_amd64 bug

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 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.
              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  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
       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.

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 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 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-index(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  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.

       [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
              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 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.

       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
              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.

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
              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 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 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 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 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
              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 supported).

              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
              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 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
              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 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  conjuction  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 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.

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)