Provided by: iproute2_4.15.0-2ubuntu1_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 | get ] dev DEV [ parent qdisc-id
       | root ] [ handle filter-id ] 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]  |
       -j[json] }

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.

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 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.

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  conjunction  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.

       -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-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)