1 .TH TC 8 "16 December 2001" "iproute2" "Linux"
3 tc \- show / manipulate traffic control settings
7 .B qdisc [ add | change | replace | link | delete ] dev
18 \fIBLOCK_INDEX\fR ] qdisc
19 [ qdisc specific parameters ]
24 .B class [ add | change | replace | delete ] dev
29 \fIclass-id\fR ] qdisc
30 [ qdisc specific parameters ]
35 .B filter [ add | change | replace | delete | get ] dev
39 .B | root ] [ handle \fIfilter-id\fR ]
43 \fIpriority\fR filtertype
44 [ filtertype specific parameters ]
50 .B filter [ add | change | replace | delete | get ] block
52 .B [ handle \fIfilter-id\fR ]
56 \fIpriority\fR filtertype
57 [ filtertype specific parameters ]
63 .B chain [ add | delete | get ] dev
67 .B | root ]\fR filtertype
68 [ filtertype specific parameters ]
72 .B chain [ add | delete | get ] block
73 \fIBLOCK_INDEX\fR filtertype
74 [ filtertype specific parameters ]
101 .RI "[ " OPTIONS " ]"
106 .RI "[ " OPTIONS " ]"
112 .RI "[ " OPTIONS " ]"
120 \fB[ -force ] -b\fR[\fIatch\fR] \fB[ filename ] \fR|
121 \fB[ \fB-n\fR[\fIetns\fR] name \fB] \fR|
122 \fB[ \fB-N\fR[\fIumeric\fR] \fB] \fR|
123 \fB[ \fB-nm \fR| \fB-nam\fR[\fIes\fR] \fB] \fR|
124 \fB[ \fR{ \fB-cf \fR| \fB-c\fR[\fIonf\fR] \fR} \fB[ filename ] \fB] \fR
125 \fB[ -t\fR[imestamp\fR] \fB\] \fR| \fB[ -t\fR[short\fR] \fR| \fB[
126 -o\fR[neline\fR] \fB]\fR }
130 \fB\-s\fR[\fItatistics\fR] |
131 \fB\-d\fR[\fIetails\fR] |
132 \fB\-r\fR[\fIaw\fR] |
133 \fB\-i\fR[\fIec\fR] |
134 \fB\-g\fR[\fIraph\fR] |
135 \fB\-j\fR[\fIjson\fR] |
136 \fB\-p\fR[\fIretty\fR] |
137 \fB\-col\fR[\fIor\fR] }
141 is used to configure Traffic Control in the Linux kernel. Traffic Control consists
146 When traffic is shaped, its rate of transmission is under control. Shaping may
147 be more than lowering the available bandwidth - it is also used to smooth out
148 bursts in traffic for better network behaviour. Shaping occurs on egress.
152 By scheduling the transmission of packets it is possible to improve interactivity
153 for traffic that needs it while still guaranteeing bandwidth to bulk transfers. Reordering
154 is also called prioritizing, and happens only on egress.
158 Whereas shaping deals with transmission of traffic, policing pertains to traffic
159 arriving. Policing thus occurs on ingress.
163 Traffic exceeding a set bandwidth may also be dropped forthwith, both on
164 ingress and on egress.
167 Processing of traffic is controlled by three kinds of objects: qdiscs,
172 is short for 'queueing discipline' and it is elementary to
173 understanding traffic control. Whenever the kernel needs to send a
174 packet to an interface, it is
176 to the qdisc configured for that interface. Immediately afterwards, the kernel
177 tries to get as many packets as possible from the qdisc, for giving them
178 to the network adaptor driver.
180 A simple QDISC is the 'pfifo' one, which does no processing at all and is a pure
181 First In, First Out queue. It does however store traffic when the network interface
182 can't handle it momentarily.
185 Some qdiscs can contain classes, which contain further qdiscs - traffic may
186 then be enqueued in any of the inner qdiscs, which are within the
188 When the kernel tries to dequeue a packet from such a
190 it can come from any of the classes. A qdisc may for example prioritize
191 certain kinds of traffic by trying to dequeue from certain classes
197 is used by a classful qdisc to determine in which class a packet will
198 be enqueued. Whenever traffic arrives at a class with subclasses, it needs
199 to be classified. Various methods may be employed to do so, one of these
200 are the filters. All filters attached to the class are called, until one of
201 them returns with a verdict. If no verdict was made, other criteria may be
202 available. This differs per qdisc.
204 It is important to notice that filters reside
206 qdiscs - they are not masters of what happens.
208 The available filters are:
211 Filter packets based on an ematch expression. See
216 Filter packets using (e)BPF, see
221 Filter packets based on the control group of their process. See
226 Flow-based classifiers, filtering packets based on their flow (identified by selectable keys). See
227 .BR tc-flow "(8) and"
232 Filter based on fwmark. Directly maps fwmark value to traffic class. See
236 Filter packets based on routing table. See
241 Match Resource Reservation Protocol (RSVP) packets.
244 Filter packets based on traffic control index. See
248 Generic filtering on arbitrary packet data, assisted by syntax to abstract common operations. See
253 Traffic control filter that matches every packet. See
258 Qdiscs may invoke user-configured actions when certain interesting events
259 take place in the qdisc. Each qevent can either be unused, or can have a
260 block attached to it. To this block are then attached filters using the "tc
261 block BLOCK_IDX" syntax. The block is executed when the qevent associated
262 with the attachment point takes place. For example, packet could be
263 dropped, or delayed, etc., depending on the qdisc and the qevent in
269 tc qdisc add dev eth0 root handle 1: red limit 500K avpkt 1K \\
270 qevent early_drop block 10
273 tc filter add block 10 matchall action mirred egress mirror dev eth1
277 The classless qdiscs are:
280 CHOKe (CHOose and Keep for responsive flows, CHOose and Kill for unresponsive
281 flows) is a classless qdisc designed to both identify and penalize flows that
282 monopolize the queue. CHOKe is a variation of RED, and the configuration is
286 CoDel (pronounced "coddle") is an adaptive "no-knobs" active queue management
287 algorithm (AQM) scheme that was developed to address the shortcomings of
288 RED and its variants.
291 Simplest usable qdisc, pure First In, First Out behaviour. Limited in
295 Fair Queue Scheduler realises TCP pacing and scales to millions of concurrent
299 Fair Queuing Controlled Delay is queuing discipline that combines Fair
300 Queuing with the CoDel AQM scheme. FQ_Codel uses a stochastic model to classify
301 incoming packets into different flows and is used to provide a fair share of the
302 bandwidth to all the flows using the queue. Each such flow is managed by the
303 CoDel queuing discipline. Reordering within a flow is avoided since Codel
304 internally uses a FIFO queue.
307 FQ-PIE (Flow Queuing with Proportional Integral controller Enhanced) is a
308 queuing discipline that combines Flow Queuing with the PIE AQM scheme. FQ-PIE
309 uses a Jenkins hash function to classify incoming packets into different flows
310 and is used to provide a fair share of the bandwidth to all the flows using the
311 qdisc. Each such flow is managed by the PIE algorithm.
314 Generalized Random Early Detection combines multiple RED queues in order to
315 achieve multiple drop priorities. This is required to realize Assured
316 Forwarding (RFC 2597).
319 Heavy-Hitter Filter differentiates between small flows and the opposite,
320 heavy-hitters. The goal is to catch the heavy-hitters and move them to a
321 separate queue with less priority so that bulk traffic does not affect the
322 latency of critical traffic.
325 This is a special qdisc as it applies to incoming traffic on an interface, allowing for it to be filtered and policed.
328 The Multiqueue Priority Qdisc is a simple queuing discipline that allows
329 mapping traffic flows to hardware queue ranges using priorities and a
330 configurable priority to traffic class mapping. A traffic class in this context
331 is a set of contiguous qdisc classes which map 1:1 to a set of hardware exposed
335 Multiqueue is a qdisc optimized for devices with multiple Tx queues. It has
336 been added for hardware that wishes to avoid head-of-line blocking. It will
337 cycle though the bands and verify that the hardware queue associated with the
338 band is not stopped prior to dequeuing a packet.
341 Network Emulator is an enhancement of the Linux traffic control facilities that
342 allow to add delay, packet loss, duplication and more other characteristics to
343 packets outgoing from a selected network interface.
346 Standard qdisc for 'Advanced Router' enabled kernels. Consists of a three-band
347 queue which honors Type of Service flags, as well as the priority that may be
348 assigned to a packet.
351 Proportional Integral controller-Enhanced (PIE) is a control theoretic active
352 queue management scheme. It is based on the proportional integral controller but
353 aims to control delay.
356 Random Early Detection simulates physical congestion by randomly dropping
357 packets when nearing configured bandwidth allocation. Well suited to very
358 large bandwidth applications.
361 Round-Robin qdisc with support for multiqueue network devices. Removed from
362 Linux since kernel version 2.6.27.
365 Stochastic Fair Blue is a classless qdisc to manage congestion based on
366 packet loss and link utilization history while trying to prevent
367 non-responsive flows (i.e. flows that do not react to congestion marking
368 or dropped packets) from impacting performance of responsive flows.
369 Unlike RED, where the marking probability has to be configured, BLUE
370 tries to determine the ideal marking probability automatically.
373 Stochastic Fairness Queueing reorders queued traffic so each 'session'
374 gets to send a packet in turn.
377 The Token Bucket Filter is suited for slowing traffic down to a precisely
378 configured rate. Scales well to large bandwidths.
379 .SH CONFIGURING CLASSLESS QDISCS
380 In the absence of classful qdiscs, classless qdiscs can only be attached at
381 the root of a device. Full syntax:
386 QDISC QDISC-PARAMETERS
396 qdisc is the automatic default in the absence of a configured qdisc.
399 The classful qdiscs are:
402 Map flows to virtual circuits of an underlying asynchronous transfer mode
406 Class Based Queueing implements a rich linksharing hierarchy of classes.
407 It contains shaping elements as well as prioritizing capabilities. Shaping is
408 performed using link idle time calculations based on average packet size and
409 underlying link bandwidth. The latter may be ill-defined for some interfaces.
412 The Deficit Round Robin Scheduler is a more flexible replacement for Stochastic
413 Fairness Queuing. Unlike SFQ, there are no built-in queues \-\- you need to add
414 classes and then set up filters to classify packets accordingly. This can be
415 useful e.g. for using RED qdiscs with different settings for particular
416 traffic. There is no default class \-\- if a packet cannot be classified, it is
420 Classify packets based on TOS field, change TOS field of packets based on
424 The ETS qdisc is a queuing discipline that merges functionality of PRIO and DRR
425 qdiscs in one scheduler. ETS makes it easy to configure a set of strict and
426 bandwidth-sharing bands to implement the transmission selection described in
430 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.
433 The Hierarchy Token Bucket implements a rich linksharing hierarchy of
434 classes with an emphasis on conforming to existing practices. HTB facilitates
435 guaranteeing bandwidth to classes, while also allowing specification of upper
436 limits to inter-class sharing. It contains shaping elements, based on TBF and
437 can prioritize classes.
440 The PRIO qdisc is a non-shaping container for a configurable number of
441 classes which are dequeued in order. This allows for easy prioritization
442 of traffic, where lower classes are only able to send if higher ones have
443 no packets available. To facilitate configuration, Type Of Service bits are
447 Quick Fair Queueing is an O(1) scheduler that provides near-optimal guarantees,
448 and is the first to achieve that goal with a constant cost also with respect to
449 the number of groups and the packet length. The QFQ algorithm has no loops, and
450 uses very simple instructions and data structures that lend themselves very
451 well to a hardware implementation.
452 .SH THEORY OF OPERATION
453 Classes form a tree, where each class has a single parent.
454 A class may have multiple children. Some qdiscs allow for runtime addition
455 of classes (CBQ, HTB) while others (PRIO) are created with a static number of
458 Qdiscs which allow dynamic addition of classes can have zero or more
459 subclasses to which traffic may be enqueued.
461 Furthermore, each class contains a
465 behaviour, although another qdisc can be attached in place. This qdisc may again
466 contain classes, but each class can have only one leaf qdisc.
468 When a packet enters a classful qdisc it can be
470 to one of the classes within. Three criteria are available, although not all
471 qdiscs will use all three:
474 If tc filters are attached to a class, they are consulted first
475 for relevant instructions. Filters can match on all fields of a packet header,
476 as well as on the firewall mark applied by ipchains or iptables.
479 Some qdiscs have built in rules for classifying packets based on the TOS field.
482 Userspace programs can encode a \fIclass-id\fR in the 'skb->priority' field using
483 the SO_PRIORITY option.
485 Each node within the tree can have its own filters but higher level filters
486 may also point directly to lower classes.
488 If classification did not succeed, packets are enqueued to the leaf qdisc
489 attached to that class. Check qdisc specific manpages for details, however.
492 All qdiscs, classes and filters have IDs, which can either be specified
493 or be automatically assigned.
496 .BR major " number and a " minor
497 number, separated by a colon -
498 .BR major ":" minor "."
500 .BR major " and " minor
501 are hexadecimal numbers and are limited to 16 bits. There are two special
502 values: root is signified by
503 .BR major " and " minor
504 of all ones, and unspecified is all zeros.
508 A qdisc, which potentially can have children, gets assigned a
510 number, called a 'handle', leaving the
512 number namespace available for classes. The handle is expressed as '10:'.
513 It is customary to explicitly assign a handle to qdiscs expected to have children.
517 Classes residing under a qdisc share their qdisc
519 number, but each have a separate
521 number called a 'classid' that has no relation to their
522 parent classes, only to their parent qdisc. The same naming custom as for
527 Filters have a three part ID, which is only needed when using a hashed
531 The following parameters are widely used in TC. For other parameters,
532 see the man pages for individual qdiscs.
537 These parameters accept a floating point number, possibly followed by
538 either a unit (both SI and IEC units supported), or a float followed by a '%'
539 character to specify the rate as a percentage of the device's speed
540 (e.g. 5%, 99.5%). Warning: specifying the rate as a percentage means a fraction
541 of the current speed; if the speed changes, the value will not be recalculated.
575 To specify in IEC units, replace the SI prefix (k-, m-, g-, t-) with
576 IEC prefix (ki-, mi-, gi- and ti-) respectively.
579 TC store rates as a 32-bit unsigned integer in bps internally,
580 so we can specify a max rate of 4294967295 bps.
585 Length of time. Can be specified as a floating point number
586 followed by an optional unit:
595 us, usec, usecs or a bare number
599 TC defined its own time unit (equal to microsecond) and stores
600 time values as 32-bit unsigned integer, thus we can specify a max time value
606 Amounts of data. Can be specified as a floating point number
607 followed by an optional unit:
632 TC stores sizes internally as 32-bit unsigned integer in byte,
633 so we can specify a max size of 4294967295 bytes.
638 Other values without a unit.
639 These parameters are interpreted as decimal by default, but you can
640 indicate TC to interpret them as octal and hexadecimal by adding a '0'
641 or '0x' prefix respectively.
644 The following commands are available for qdiscs, classes and filter:
647 Add a qdisc, class or filter to a node. For all entities, a
649 must be passed, either by passing its ID or by attaching directly to the root of a device.
650 When creating a qdisc or a filter, it can be named with the
652 parameter. A class is named with the
658 A qdisc can be deleted by specifying its handle, which may also be 'root'. All subclasses and their leaf qdiscs
659 are automatically deleted, as well as any filters attached to them.
663 Some entities can be modified 'in place'. Shares the syntax of 'add', with the exception
664 that the handle cannot be changed and neither can the parent. In other words,
671 Performs a nearly atomic remove/add on an existing node id. If the node does not exist yet
676 Displays a single filter given the interface \fIDEV\fR, \fIqdisc-id\fR,
677 \fIpriority\fR, \fIprotocol\fR and \fIfilter-id\fR.
681 Displays all filters attached to the given interface. A valid parent ID must be passed.
685 Only available for qdiscs and performs a replace where the node
689 The\fB\ tc\fR\ utility can monitor events generated by the kernel such as
690 adding/deleting qdiscs, filters or actions, or modifying existing ones.
692 The following command is available for\fB\ monitor\fR\ :
695 If the file option is given, the \fBtc\fR does not listen to kernel events, but opens
696 the given file and dumps its contents. The file has to be in binary
697 format and contain netlink messages.
702 .BR "\-b", " \-b filename", " \-batch", " \-batch filename"
703 read commands from provided file or standard input and invoke them.
704 First failure will cause termination of tc.
708 don't terminate tc on errors in batch mode.
709 If there were any errors during execution of the commands, the application return code will be non zero.
712 .BR "\-o" , " \-oneline"
713 output each record on a single line, replacing line feeds
716 character. This is convenient when you want to count records
724 .BR "\-n" , " \-net" , " \-netns " <NETNS>
727 to the specified network namespace
729 Actually it just simplifies executing of:
734 .RI "[ " OPTIONS " ] " OBJECT " { " COMMAND " | "
740 .RI "-n[etns] " NETNS " [ " OPTIONS " ] " OBJECT " { " COMMAND " | "
744 .BR "\-N" , " \-Numeric"
745 Print the number of protocol, scope, dsfield, etc directly instead of
746 converting it to human readable name.
749 .BR "\-cf" , " \-conf " <FILENAME>
750 specifies path to the config file. This option is used in conjunction with other options (e.g.
754 .BR "\-t", " \-timestamp"
755 When\fB\ tc monitor\fR\ runs, print timestamp before the event message in format:
756 Timestamp: <Day> <Month> <DD> <hh:mm:ss> <YYYY> <usecs> usec
759 .BR "\-ts", " \-tshort"
760 When\fB\ tc monitor\fR\ runs, prints short timestamp before the event message in format:
761 [<YYYY>-<MM>-<DD>T<hh:mm:ss>.<ms>]
764 The show command has additional formatting options:
767 .BR "\-s" , " \-stats", " \-statistics"
768 output more statistics about packet usage.
771 .BR "\-d", " \-details"
772 output more detailed information about rates and cell sizes.
776 output raw hex values for handles.
779 .BR "\-p", " \-pretty"
780 for u32 filter, decode offset and mask values to equivalent filter commands based on TCP/IP.
781 In JSON output, add whitespace to improve readability.
785 print rates in IEC units (ie. 1K = 1024).
788 .BR "\-g", " \-graph"
789 shows classes as ASCII graph. Prints generic stats info under each class if
791 option was specified. Classes can be filtered only by
796 .BR \-c [ color ][ = { always | auto | never }
797 Configure color output. If parameter is omitted or
799 color output is enabled regardless of stdout state. If parameter is
801 stdout is checked to be a terminal before enabling color output. If parameter is
803 color output is disabled. If specified multiple times, the last one takes
804 precedence. This flag is ignored if
810 Display results in JSON format.
813 .BR "\-nm" , " \-name"
814 resolve class name from
815 .B /etc/iproute2/tc_cls
816 file or from file specified by
818 option. This file is just a mapping of
826 1:40 voip # Here is another comment
842 was specified without
845 .B /etc/iproute2/tc_cls
846 file does not exist, which makes it possible to pass
855 tc -g class show dev eth0
857 Shows classes as ASCII graph on eth0 interface.
860 tc -g -s class show dev eth0
862 Shows classes as ASCII graph with stats info under each class.
867 was written by Alexey N. Kuznetsov and added in Linux 2.2.
891 .BR tc-pfifo_fast (8),
902 .RB "User documentation at " http://lartc.org/ ", but please direct bugreports and patches to: " <netdev@vger.kernel.org>
905 Manpage maintained by bert hubert (ahu@ds9a.nl)
projects / mirror_iproute2.git / blob