TC(8)                  (16 December 2001)                   TC(8)

          tc - show / manipulate traffic control settings

          tc [ OPTIONS ] qdisc [ add | change | 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 | DEV parent qdisc-id [
          classid class-id ] qdisc [ qdisc specific parameters ]

          tc [ OPTIONS ] filter [ add | change | DEV [ parent qdisc-id
          | root ] [ handle filter-id protocol protocol prio priority
          filtertype [ filtertype specific parameters ] flowid flow-id

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

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

          tc [ OPTIONS ] chain [ add | delete | BLOCK_INDEX filtertype
          [ filtertype specific parameters ]

          tc [ OPTIONS ] [ FORMAT ] qdisc { show | list } DEV ] [ root
          | ingress | 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]

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          | -g[raph] | -j[json] | -p[retty] | -col[or] }

          Tc is used to configure Traffic Control in the Linux kernel.
          Traffic Control consists of the following:

               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.

               By scheduling the transmission of packets it is possi-
               ble 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.

               Whereas shaping deals with transmission of traffic,
               policing pertains to traffic arriving. Policing thus
               occurs on ingress.

               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.

          qdisc is short for 'queueing discipline' and it is elemen-
          tary 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 after-
          wards, the kernel tries to get as many packets as possible
          from the qdisc, for giving them to the network adaptor

          A simple QDISC is the 'pfifo' one, which does no processing
          at all and is a pure First In, First Out queue. It does how-
          ever store traffic when the network interface can't handle
          it momentarily.

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          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.

          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 fil-
          ters. 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:

               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.

               Filter packets based on the control group of their pro-
               cess. 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).

               Filter packets based on routing table. See tc-route(8)
               for details.

          rsvp Match Resource Reservation Protocol (RSVP) packets.

               Filter packets based on traffic control index. See

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          u32  Generic filtering on arbitrary packet data, assisted by
               syntax to abstract common operations. See tc-u32(8) for

               Traffic control filter that matches every packet. See
               tc-matchall(8) for details.

          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 exam-
          ple, 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

          The classless qdiscs are:

               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 (pronounced "coddle") is an adaptive "no-knobs"
               active queue management algorithm (AQM) scheme that was
               developed to address the shortcomings of RED and its

               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.


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               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 (Flow Queuing with Proportional Integral con-
               troller 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 priori-
               ties. 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.

               This is a special qdisc as it applies to incoming traf-
               fic on an interface, allowing for it to be filtered and

               The Multiqueue Priority Qdisc is a simple queuing dis-
               cipline that allows mapping traffic flows to hardware
               queue ranges using priorities and a configurable prior-
               ity 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.

               Multiqueue is a qdisc optimized for devices with multi-
               ple 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.

               Network Emulator is an enhancement of the Linux traffic

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               control facilities that allow to add delay, packet
               loss, duplication and more other characteristics to
               packets outgoing from a selected network interface.

               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 band-
               width allocation. Well suited to very large bandwidth

          rr   Round-Robin qdisc with support for multiqueue network
               devices. Removed from Linux since kernel version

          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 respon-
               sive 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.

          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.

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          The classful qdiscs are:

          ATM  Map flows to virtual circuits of an underlying asyn-
               chronous 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.

               Classify packets based on TOS field, change TOS field
               of packets based on classification.

          ETS  The ETS qdisc is a queuing discipline that merges func-
               tionality 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 linkshar-
               ing 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

          PRIO The PRIO qdisc is a non-shaping container for a config-
               urable 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.

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          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 algo-
               rithm has no loops, and uses very simple instructions
               and data structures that lend themselves very well to a
               hardware implementation.

          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 con-
               sulted 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.

               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

          If classification did not succeed, packets are enqueued to
          the leaf qdisc attached to that class. Check qdisc specific
          manpages for details, however.

          All qdiscs, classes and filters have IDs, which can either
          be specified or be automatically assigned.

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          IDs consist of a major number and a minor number, separated
          by a colon - major:minor.  Both major and minor are hexadec-
          imal numbers and are limited to 16 bits. There are two spe-
          cial values: root is signified by major and minor of all
          ones, and unspecified is all zeros.

               A qdisc, which potentially can have children, gets
               assigned a major number, called a 'handle', leaving the
               minor number namespace available for classes. The han-
               dle is expressed as '10:'.  It is customary to explic-
               itly assign a handle to qdiscs expected to have chil-

               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 have a three part ID, which is only needed when
               using a hashed filter hierarchy.

          The following parameters are widely used in TC. For other
          parameters, see the man pages for individual qdiscs.

               Bandwidths or rates.  These parameters accept a float-
               ing 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: speci-
               fying 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

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               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-) respec-

               TC store rates as a 32-bit unsigned integer in bps
               internally, so we can specify a max rate of 4294967295

               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

               us, usec, usecs or a bare number

               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.

               Amounts of data. Can be specified as a floating point
               number followed by an optional unit:

               b or a bare number

               kbit Kilobits

               kb or k

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     TC(8)                  (16 December 2001)                   TC(8)


               mbit Megabits

               mb or m

               gbit Gigabits

               gb or g

               TC stores sizes internally as 32-bit unsigned integer
               in byte, so we can specify a max size of 4294967295

               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.

          The following commands are available for qdiscs, classes and

          add  Add a qdisc, class or filter to a node. For all enti-
               ties, 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

               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 fil-
               ters attached to them.

               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.


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               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.

          The tc utility can monitor events generated by the kernel
          such as adding/deleting qdiscs, filters or actions, or modi-
          fying 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 con-
               tain netlink messages.

          -b, -b filename, -batch,
               read commands from provided file or standard input and
               invoke them.  First failure will cause termination of

               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

          -n, -net, -netns <NETNS>
               switches tc to the specified network namespace NETNS.
               Actually it just simplifies executing of:

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     TC(8)                  (16 December 2001)                   TC(8)

               ip netns exec NETNS tc [ OPTIONS ] OBJECT { COMMAND
               help }


               tc -n[etns] NETNS [ OPTIONS ] OBJECT help }

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

          -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:

          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

          -r, -raw
               output raw hex values for handles.

          -p, -pretty
               for u32 filter, decode offset and mask values to equiv-
               alent filter commands based on TCP/IP.  In JSON output,

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               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.

               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.

          tc -g class show dev eth0

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              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

          tc was written by Alexey N. Kuznetsov and added in Linux

          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),
          User documentation at, but please direct
          bugreports and patches to: <>

          Manpage maintained by bert hubert (

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