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1 perry 1 TC
2 !!!TC
3 NAME
4 SYNOPSIS
5 DESCRIPTION
6 QDISCS
7 CLASSES
8 FILTERS
9 CLASSLESS QDISCS
10 CONFIGURING CLASSLESS QDISCS
11 CLASSFUL QDISCS
12 THEORY OF OPERATION
13 NAMING
14 UNITS
15 TC COMMANDS
16 HISTORY
17 SEE ALSO
18 AUTHOR
19 ----
20 !!NAME
21
22
23 tc - show / manipulate traffic control settings
24 !!SYNOPSIS
25
26
27 __tc qdisc [[ add | change | replace | link ] dev__ DEV
28 __[[ parent__ qdisc-id __| root ] [[ handle__ qdisc-id ]
29 qdisc [[ qdisc specific parameters ]
30
31
32 __tc class [[ add | change | replace ] dev__ DEV
33 __parent__ qdisc-id __[[ classid__ class-id ] qdisc [[
34 qdisc specific parameters ]
35
36
37 __tc filter [[ add | change | replace ] dev__ DEV __[[
38 parent__ qdisc-id __| root ] protocol__ protocol
39 __prio__ priority filtertype [[ filtertype specific
40 parameters ] __flowid__ flow-id
41
42
43 __tc [[-s | -d ] qdisc show [[ dev__ DEV
44 __]__
45
46
47 __tc [[-s | -d ] class show dev__ DEV
48
49
50 __tc filter show dev__ DEV
51 !!DESCRIPTION
52
53
54 __Tc__ is used to configure Traffic Control in the Linux
55 kernel. Traffic Control consists of the
56 following:
57
58
59 SHAPING
60
61
62 When traffic is shaped, its rate of transmission is under
63 control. Shaping may be more than lowering the available
64 bandwidth - it is also used to smooth out bursts in traffic
65 for better network behaviour. Shaping occurs on
66 egress.
67
68
69 SCHEDULING
70
71
72 By scheduling the transmission of packets it is possible to
73 improve interactivity for traffic that needs it while still
74 guaranteeing bandwidth to bulk transfers. Reordering is also
75 called prioritizing, and happens only on
76 egress.
77
78
79 POLICING
80
81
82 Where shaping deals with transmission of traffic, policing
83 pertains to traffic arriving. Policing thus occurs on
84 ingress.
85
86
87 DROPPING
88
89
90 Traffic exceeding a set bandwidth may also be dropped
91 forthwith, both on ingress and on egress.
92
93
94 Processing of traffic is controlled by three kinds of
95 objects: qdiscs, classes and filters.
96 !!QDISCS
97
98
99 __qdisc__ is short for 'queueing discipline' and it is
100 elementary to understanding traffic control. Whenever the
101 kernel needs to send a packet to an interface, it is
102 __enqueued__ to the qdisc configured for that interface.
103 Immediately afterwards, the kernel tries to get as many
104 packets as possible from the qdisc, for giving them to the
105 network adaptor driver.
106
107
108 A simple QDISC is the 'pfifo' one, which does no processing
109 at all and is a pure First In, First Out queue. It does
110 however store traffic when the network interface can't
111 handle it momentarily.
112 !!CLASSES
113
114
115 Some qdiscs can contain classes, which contain further
116 qdiscs - traffic may then be enqueued in any of the inner
117 qdiscs, which are within the __classes.__ When the kernel
118 tries to dequeue a packet from such a __classful qdisc__
119 it can come from any of the classes. A qdisc may for example
120 prioritize certain kinds of traffic by trying to dequeue
121 from certain classes before others.
122 !!FILTERS
123
124
125 A __filter__ is used by a classful qdisc to determine in
126 which class a packet will be enqueued. Whenever traffic
127 arrives at a class with subclasses, it needs to be
128 classified. Various methods may be employed to do so, one of
129 these are the filters. All filters attached to the class are
130 called, until one of them returns with a verdict. If no
131 verdict was made, other criteria may be available. This
132 differs per qdisc.
133
134
135 It is important to notice that filters reside __within__
136 qdiscs - they are not masters of what happens.
137 !!CLASSLESS QDISCS
138
139
140 The classless qdiscs are:
141
142
143 [[p|b]fifo
144
145
146 Simplest usable qdisc, pure First In, First Out behaviour.
147 Limited in packets or in bytes.
148
149
150 pfifo_fast
151
152
153 Standard qdisc for 'Advanced Router' enabled kernels.
154 Consists of a three-band queue which honors Type of Service
155 flags, as well as the priority that may be assigned to a
156 packet.
157
158
159 red
160
161
162 Random Early Detection simulates physical congestion by
163 randomly dropping packets when nearing configured bandwidth
164 allocation. Well suited to very large bandwidth
165 applications.
166
167
168 sfq
169
170
171 Stochastic Fairness Queueing reorders queued traffic so each
172 'session' gets to send a packet in turn.
173
174
175 tbf
176
177
178 The Token Bucket Filter is suited for slowing traffic down
179 to a precisely configured rate. Scales well to large
180 bandwidths.
181 !!CONFIGURING CLASSLESS QDISCS
182
183
184 In the absence of classful qdiscs, classless qdiscs can only
185 be attached at the root of a device. Full
186 syntax:
187
188
189 __tc qdisc add dev__ DEV __root__ QDISC
190 QDISC-PARAMETERS
191
192
193 To remove, issue
194
195
196 __tc qdisc del dev__ DEV __root__
197
198
199 The __pfifo_fast__ qdisc is the automatic default in the
200 absence of a configured qdisc.
201 !!CLASSFUL QDISCS
202
203
204 The classful qdiscs are:
205
206
207 CBQ
208
209
210 Class Based Queueing implements a rich linksharing hierarchy
211 of classes. It contains shaping elements as well as
212 prioritizing capabilities. Shaping is performed using link
213 idle time calculations based on average packet size and
214 underlying link bandwidth. The latter may be ill-defined for
215 some interfaces.
216
217
218 HTB
219
220
221 The Hierarchy Token Bucket implements a rich linksharing
222 hierarchy of classes with an emphasis on conforming to
223 existing practices. HTB facilitates guaranteeing bandwidth
224 to classes, while also allowing specification of upper
225 limits to inter-class sharing. It contains shaping elements,
226 based on TBF and can prioritize classes.
227
228
229 PRIO
230
231
232 The PRIO qdisc is a non-shaping container for a configurable
233 number of classes which are dequeued in order. This allows
234 for easy prioritization of traffic, where lower classes are
235 only able to send if higher ones have no packets available.
236 To facilitate configuration, Type Of Service bits are
237 honored by default.
238 !!THEORY OF OPERATION
239
240
241 Classes form a tree, where each class has a single parent. A
242 class may have multiple children. Some qdiscs allow for
243 runtime addition of classes (CBQ, HTB) while others (PRIO)
244 are created with a static number of children.
245
246
247 Qdiscs which allow dynamic addition of classes can have zero
248 or more subclasses to which traffic may be
249 enqueued.
250
251
252 Furthermore, each class contains a __leaf qdisc__ which
253 by default has __pfifo__ behaviour though another qdisc
254 can be attached in place. This qdisc may again contain
255 classes, but each class can have only one leaf
256 qdisc.
257
258
259 When a packet enters a classful qdisc it can be
260 __classified__ to one of the classes within. Three
261 criteria are available, although not all qdiscs will use all
262 three:
263
264
265 tc filters
266
267
268 If tc filters are attached to a class, they are consulted
269 first for relevant instructions. Filters can match on all
270 fields of a packet header, as well as on the firewall mark
271 applied by ipchains or iptables. See
272 tc-filters(8).
273
274
275 Type of Service
276
277
278 Some qdiscs have built in rules for classifying packets
279 based on the TOS field.
280
281
282 skb-
283
284
285 Userspace programs can encode a class-id in the
286 'skb-
287
288
289 Each node within the tree can have its own filters but
290 higher level filters may also point directly to lower
291 classes.
292
293
294 If classification did not succeed, packets are enqueued to
295 the leaf qdisc attached to that class. Check qdisc specific
296 manpages for details, however.
297 !!NAMING
298
299
300 All qdiscs, classes and filters have IDs, which can either
301 be specified or be automatically assigned.
302
303
304 IDs consist of a major number and a minor number, separated
305 by a colon.
306
307
308 QDISCS
309
310
311 A qdisc, which potentially can have children, gets assigned
312 a major number, called a 'handle', leaving the minor number
313 namespace available for classes. The handle is expressed as
314 '10:'. It is customary to explicitly assign a handle to
315 qdiscs expected to have children.
316
317
318 CLASSES
319
320
321 Classes residing under a qdisc share their qdisc major
322 number, but each have a separate minor number called a
323 'classid' that has no relation to their parent classes, only
324 to their parent qdisc. The same naming custom as for qdiscs
325 applies.
326
327
328 FILTERS
329
330
331 Filters have a three part ID, which is only needed when
332 using a hashed filter hierarchy, for which see
333 tc-filters(8).
334 !!UNITS
335
336
337 All parameters accept a floating point number, possibly
338 followed by a unit.
339
340
341 Bandwidths or rates can be specified in:
342
343
344 kbps
345
346
347 Kilobytes per second
348
349
350 mbps
351
352
353 Megabytes per second
354
355
356 kbit
357
358
359 Kilobits per second
360
361
362 mbit
363
364
365 Megabits per second
366
367
368 bps or a bare number
369
370
371 Bits per second
372
373
374 Amounts of data can be specified in:
375
376
377 kb or k
378
379
380 Kilobytes
381
382
383 mb or m
384
385
386 Megabytes
387
388
389 mbit
390
391
392 Megabits
393
394
395 kbit
396
397
398 Kilobits
399
400
401 b or a bare number
402
403
404 Bytes.
405
406
407 Lengths of time can be specified in:
408
409
410 s, sec or secs
411
412
413 Whole seconds
414
415
416 ms, msec or msecs
417
418
419 Milliseconds
420
421
422 us, usec, usecs or a bare number
423
424
425 Microseconds.
426 !!TC COMMANDS
427
428
429 The following commands are available for qdiscs, classes and
430 filter:
431
432
433 add
434
435
436 Add a qdisc, class or filter to a node. For all entities, a
437 __parent__ must be passed, either by passing its ID or by
438 attaching directly to the root of a device. When creating a
439 qdisc or a filter, it can be named with the __handle__
440 parameter. A class is named with the __classid__
441 parameter.
442
443
444 remove
445
446
447 A qdisc can be removed by specifying its handle, which may
448 also be 'root'. All subclasses and their leaf qdiscs are
449 automatically deleted, as well as any filters attached to
450 them.
451
452
453 change
454
455
456 Some entities can be modified 'in place'. Shares the syntax
457 of 'add', with the exception that the handle cannot be
458 changed and neither can the parent. In other words,
459 __change__ cannot move a node.
460
461
462 replace
463
464
465 Performs a nearly atomic remove/add on an existing node id.
466 If the node does not exist yet it is created.
467
468
469 link
470
471
472 Only available for qdiscs and performs a replace where the
473 node must exist already.
474 !!HISTORY
475
476
477 __tc__ was written by Alexey N. Kuznetsov and added in
478 Linux 2.2.
479 !!SEE ALSO
480
481
482 tc-cbq(8), tc-htb(8), tc-sfq(8),
483 tc-red(8), tc-tbf(8), tc-pfifo(8),
484 tc-bfifo(8), tc-pfifo_fast(8),
485 tc-filters(8)
486 !!AUTHOR
487
488
489 Manpage maintained by bert hubert (ahu@ds9a.nl)
490 ----
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