# tc

## 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 | show ]**
           **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] **]** | **[**
           **-echo ]**}
    
            _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.
    
           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 one 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.
    
           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.
    
           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.
    
           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 (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>]
    
           **-echo** Request the kernel to send the applied configuration back.
    


## 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.
    
           **-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.
    


* * *