Provided by: iproute2_5.10.0-4ubuntu1_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 ] [ 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
       specific 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
       specific 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.
              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-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
       executed 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
       question.

       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
              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.

       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
              Jenkins 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-
              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.

       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
              bandwidth-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
              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 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 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
              current 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
              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.

       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
              execution 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
              output.

       -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
              option 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
              terminal 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
              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-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@vger.kernel.org>

AUTHOR

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