1CAKE(8)                              Linux                             CAKE(8)
2
3
4

NAME

6       CAKE - Common Applications Kept Enhanced (CAKE)
7

SYNOPSIS

9       tc qdisc ... cake
10       [ bandwidth RATE | unlimited* | autorate-ingress ]
11       [  rtt TIME | datacentre | lan | metro | regional | internet* | oceanic
12       | satellite | interplanetary ]
13       [ besteffort | diffserv8 | diffserv4 | diffserv3* ]
14       [ flowblind | srchost | dsthost | hosts | flows | dual-srchost |  dual-
15       dsthost | triple-isolate* ]
16       [ nat | nonat* ]
17       [ wash | nowash* ]
18       [ split-gso* | no-split-gso ]
19       [ ack-filter | ack-filter-aggressive | no-ack-filter* ]
20       [ memlimit LIMIT ]
21       [ fwmark MASK ]
22       [ ptm | atm | noatm* ]
23       [ overhead N | conservative | raw* ]
24       [ mpu N ]
25       [ ingress | egress* ]
26       (* marks defaults)
27
28
29

DESCRIPTION

31       CAKE  (Common  Applications  Kept  Enhanced) is a shaping-capable queue
32       discipline which uses both AQM and FQ.  It combines COBALT, which is an
33       AQM  algorithm  combining  Codel  and  BLUE, a shaper which operates in
34       deficit mode, and a variant of DRR++ for flow  isolation.   8-way  set-
35       associative  hashing  is  used  to virtually eliminate hash collisions.
36       Priority queuing is available through a simplified diffserv implementa‐
37       tion.   Overhead  compensation  for  various  encapsulation  schemes is
38       tightly integrated.
39
40       All settings are optional; the default settings are chosen to be sensi‐
41       ble  in most common deployments.  Most people will only need to set the
42       bandwidth parameter to get useful results,  but  reading  the  Overhead
43       Compensation and Round Trip Time sections is strongly encouraged.
44
45

SHAPER PARAMETERS

47       CAKE  uses  a  deficit-mode  shaper, which does not exhibit the initial
48       burst typical of token-bucket shapers.   It  will  automatically  burst
49       precisely  as  much  as required to maintain the configured throughput.
50       As such, it is very straightforward to configure.
51
52       unlimited (default)
53            No limit on the bandwidth.
54
55       bandwidth RATE
56            Set the shaper bandwidth.  See tc(8) or examples below for details
57       of the RATE value.
58
59       autorate-ingress
60            Automatic  capacity  estimation  based on traffic arriving at this
61       qdisc.  This is most likely to be useful  with  cellular  links,  which
62       tend  to change quality randomly.  A bandwidth parameter can be used in
63       conjunction to specify an initial estimate.  The shaper  will  periodi‐
64       cally  be  set  to a bandwidth slightly below the estimated rate.  This
65       estimator cannot estimate the bandwidth of links downstream of itself.
66
67

OVERHEAD COMPENSATION PARAMETERS

69       The size of each packet on the wire may differ from that seen by Linux.
70       The  following  parameters allow CAKE to compensate for this difference
71       by internally considering each packet to be bigger than  Linux  informs
72       it.   To  assist  users  who are not expert network engineers, keywords
73       have been provided to represent a number of common link technologies.
74
75
76   Manual Overhead Specification
77       overhead BYTES
78            Adds BYTES to the size of each packet.   BYTES  may  be  negative;
79       values between -64 and 256 (inclusive) are accepted.
80
81       mpu BYTES
82            Rounds  each  packet  (including  overhead) up to a minimum length
83       BYTES. BYTES may not be negative; values between 0 and 256  (inclusive)
84       are accepted.
85
86       atm
87            Compensates  for ATM cell framing, which is normally found on ADSL
88       links.  This is performed after the overhead parameter above.  ATM uses
89       fixed 53-byte cells, each of which can carry 48 bytes payload.
90
91       ptm
92            Compensates  for  PTM  encoding,  which is normally found on VDSL2
93       links and uses a 64b/65b encoding scheme. It is even more efficient  to
94       simply  derate  the  specified shaper bandwidth by a factor of 64/65 or
95       0.984. See ITU G.992.3 Annex N and IEEE 802.3 Section 61.3 for details.
96
97       noatm
98            Disables ATM and PTM compensation.
99
100
101   Failsafe Overhead Keywords
102       These two keywords are provided for quick-and-dirty setup.  Use them if
103       you can't be bothered to read the rest of this section.
104
105       raw (default)
106            Turns  off  all  overhead  compensation  in CAKE.  The packet size
107       reported by Linux will be used directly.
108
109            Other overhead keywords may be added after "raw".  The  effect  of
110       this  is  to  make  the  overhead  compensation operate relative to the
111       reported packet size, not the underlying IP packet size.
112
113       conservative
114            Compensates for more overhead than  is  likely  to  occur  on  any
115       widely-deployed link technology.
116            Equivalent to overhead 48 atm.
117
118
119   ADSL Overhead Keywords
120       Most  ADSL  modems  have a way to check which framing scheme is in use.
121       Often this is also specified in the settings document provided  by  the
122       ISP.   The  keywords  in  this  section are intended to correspond with
123       these sources of information.  All of them implicitly set the atm flag.
124
125       pppoa-vcmux
126            Equivalent to overhead 10 atm
127
128       pppoa-llc
129            Equivalent to overhead 14 atm
130
131       pppoe-vcmux
132            Equivalent to overhead 32 atm
133
134       pppoe-llcsnap
135            Equivalent to overhead 40 atm
136
137       bridged-vcmux
138            Equivalent to overhead 24 atm
139
140       bridged-llcsnap
141            Equivalent to overhead 32 atm
142
143       ipoa-vcmux
144            Equivalent to overhead 8 atm
145
146       ipoa-llcsnap
147            Equivalent to overhead 16 atm
148
149       See also the Ethernet Correction Factors section below.
150
151
152   VDSL2 Overhead Keywords
153       ATM was dropped from VDSL2 in favour of  PTM,  which  is  a  much  more
154       straightforward  framing scheme.  Some ISPs retained PPPoE for compati‐
155       bility with their existing back-end systems.
156
157       pppoe-ptm
158            Equivalent to overhead 30 ptm
159
160            PPPoE: 2B PPP + 6B PPPoE +
161            ETHERNET: 6B dest MAC + 6B src MAC + 2B ethertype + 4B Frame Check
162       Sequence +
163            PTM:  1B  Start  of  Frame  (S) + 1B End of Frame (Ck) + 2B TC-CRC
164       (PTM-FCS)
165
166       bridged-ptm
167            Equivalent to overhead 22 ptm
168            ETHERNET: 6B dest MAC + 6B src MAC + 2B ethertype + 4B Frame Check
169       Sequence +
170            PTM:  1B  Start  of  Frame  (S) + 1B End of Frame (Ck) + 2B TC-CRC
171       (PTM-FCS)
172
173       See also the Ethernet Correction Factors section below.
174
175
176   DOCSIS Cable Overhead Keyword
177       DOCSIS is the universal standard for providing  Internet  service  over
178       cable-TV infrastructure.
179
180       In  this  case,  the actual on-wire overhead is less important than the
181       packet size the head-end equipment uses for shaping and metering.  This
182       is specified to be an Ethernet frame including the CRC (aka FCS).
183
184       docsis
185            Equivalent to overhead 18 mpu 64 noatm
186
187
188   Ethernet Overhead Keywords
189       ethernet
190            Accounts for Ethernet's preamble, inter-frame gap, and Frame Check
191       Sequence.  Use this keyword when the bottleneck being shaped for is  an
192       actual Ethernet cable.
193            Equivalent to overhead 38 mpu 84 noatm
194
195       ether-vlan
196            Adds  4 bytes to the overhead compensation, accounting for an IEEE
197       802.1Q VLAN header appended to the Ethernet  frame  header.   NB:  Some
198       ISPs  use  one  or  even two of these within PPPoE; this keyword may be
199       repeated as necessary to express this.
200
201

ROUND TRIP TIME PARAMETERS

203       Active Queue Management (AQM) consists of embedding congestion  signals
204       in  the  packet  flow,  which receivers use to instruct senders to slow
205       down when the queue is persistently occupied.  CAKE uses ECN signalling
206       when  available, and packet drops otherwise, according to a combination
207       of the Codel and BLUE AQM algorithms called COBALT.
208
209       Very short latencies require a very rapid AQM  response  to  adequately
210       control  latency.   However,  such  a  rapid  response  tends to impair
211       throughput when the actual RTT is relatively long.  CAKE allows  speci‐
212       fying  the  RTT  it assumes for tuning various parameters.  Actual RTTs
213       within an order of magnitude of this will generally work well for  both
214       throughput and latency management.
215
216       At  the 'lan' setting and below, the time constants are similar in mag‐
217       nitude to the jitter in the Linux kernel itself, so congestion might be
218       signalled  prematurely.  The  flows  will  then become sparse and total
219       throughput reduced, leaving little or no back-pressure for the fairness
220       logic  to  work  against. Use the "metro" setting for local lans unless
221       you have a custom kernel.
222
223       rtt TIME
224            Manually specify an RTT.
225
226       datacentre
227            For extremely high-performance 10GigE+ networks only.   Equivalent
228       to rtt 100us.
229
230       lan
231            For  pure Ethernet (not Wi-Fi) networks, at home or in the office.
232       Don't use this when shaping for an Internet access link.  Equivalent to
233       rtt 1ms.
234
235       metro
236            For traffic mostly within a single city.  Equivalent to rtt 10ms.
237
238       regional
239            For traffic mostly within a European-sized country.  Equivalent to
240       rtt 30ms.
241
242       internet (default)
243            This is suitable for most Internet  traffic.   Equivalent  to  rtt
244       100ms.
245
246       oceanic
247            For Internet traffic with generally above-average latency, such as
248       that suffered by Australasian residents.  Equivalent to rtt 300ms.
249
250       satellite
251            For traffic  via  geostationary  satellites.   Equivalent  to  rtt
252       1000ms.
253
254       interplanetary
255            So  named  because  Jupiter is about 1 light-hour from Earth.  Use
256       this to (almost) completely disable AQM  actions.   Equivalent  to  rtt
257       3600s.
258
259

FLOW ISOLATION PARAMETERS

261       With  flow  isolation enabled, CAKE places packets from different flows
262       into different queues, each of which carries its own AQM state.   Pack‐
263       ets  from  each  queue  are then delivered fairly, according to a DRR++
264       algorithm which minimises latency for "sparse" flows.  CAKE uses a set-
265       associative hashing algorithm to minimise flow collisions.
266
267       These keywords specify whether fairness based on source address, desti‐
268       nation address, individual  flows,  or  any  combination  of  those  is
269       desired.
270
271       flowblind
272            Disables flow isolation; all traffic passes through a single queue
273       for each tin.
274
275       srchost
276            Flows are defined only by source address.  Could be useful on  the
277       egress path of an ISP backhaul.
278
279       dsthost
280            Flows are defined only by destination address.  Could be useful on
281       the ingress path of an ISP backhaul.
282
283       hosts
284            Flows are defined by source-destination host pairs.  This is  host
285       isolation, rather than flow isolation.
286
287       flows
288            Flows  are defined by the entire 5-tuple of source address, desti‐
289       nation address, transport protocol, source port and  destination  port.
290       This is the type of flow isolation performed by SFQ and fq_codel.
291
292       dual-srchost
293            Flows  are  defined  by the 5-tuple, and fairness is applied first
294       over source addresses, then over individual flows.   Good  for  use  on
295       egress  traffic from a LAN to the internet, where it'll prevent any one
296       LAN host from monopolising the uplink,  regardless  of  the  number  of
297       flows they use.
298
299       dual-dsthost
300            Flows  are  defined  by the 5-tuple, and fairness is applied first
301       over destination addresses, then over individual flows.  Good  for  use
302       on  ingress traffic to a LAN from the internet, where it'll prevent any
303       one LAN host from monopolising the downlink, regardless of  the  number
304       of flows they use.
305
306       triple-isolate (default)
307            Flows  are  defined  by  the 5-tuple, and fairness is applied over
308       source *and* destination addresses intelligently  (ie.  not  merely  by
309       host-pairs),  and  also  over individual flows.  Use this if you're not
310       certain whether to use dual-srchost or dual-dsthost; it'll do both jobs
311       at  once,  preventing  any  one  host on *either* side of the link from
312       monopolising it with a large number of flows.
313
314       nat
315            Instructs Cake to perform a NAT lookup before applying flow-isola‐
316       tion  rules,  to  determine  the true addresses and port numbers of the
317       packet, to improve fairness between hosts "inside" the NAT.   This  has
318       no  practical effect in "flowblind" or "flows" modes, or if NAT is per‐
319       formed on a different host.
320
321       nonat (default)
322            Cake will not perform a NAT lookup.  Flow isolation will  be  per‐
323       formed  using  the  addresses  and port numbers directly visible to the
324       interface Cake is attached to.
325
326

PRIORITY QUEUE PARAMETERS

328       CAKE can divide traffic into "tins" based on the Diffserv field.   Each
329       tin  has  its own independent set of flow-isolation queues, and is ser‐
330       viced based on a WRR algorithm.  To  avoid  perverse  Diffserv  marking
331       incentives,  tin weights have a "priority sharing" value when bandwidth
332       used by that tin is below a threshold, and a lower "bandwidth  sharing"
333       value  when  above.   Bandwidth is compared against the threshold using
334       the same algorithm as the deficit-mode shaper.
335
336       Detailed customisation of tin parameters is not provided.  The  follow‐
337       ing  presets  perform  all  necessary  tuning,  relative to the current
338       shaper bandwidth and RTT settings.
339
340       besteffort
341            Disables priority queuing by placing all traffic in one tin.
342
343       precedence
344            Enables legacy interpretation of TOS "Precedence" field.   Use  of
345       this preset on the modern Internet is firmly discouraged.
346
347       diffserv4
348            Provides a general-purpose Diffserv implementation with four tins:
349                 Bulk (CS1), 6.25% threshold, generally low priority.
350                 Best Effort (general), 100% threshold.
351                 Video  (AF4x,  AF3x, CS3, AF2x, CS2, TOS4, TOS1), 50% thresh‐
352       old.
353                 Voice (CS7, CS6, EF, VA, CS5, CS4), 25% threshold.
354
355       diffserv3 (default)
356            Provides a simple, general-purpose  Diffserv  implementation  with
357       three tins:
358                 Bulk (CS1), 6.25% threshold, generally low priority.
359                 Best Effort (general), 100% threshold.
360                 Voice  (CS7, CS6, EF, VA, TOS4), 25% threshold, reduced Codel
361       interval.
362
363
364       fwmark MASK
365            This options turns on fwmark-based overriding of CAKE's tin selec‐
366       tion.   If  set, the option specifies a bitmask that will be applied to
367       the fwmark associated with each packet. If the result of  this  masking
368       is  non-zero,  the result will be right-shifted by the number of least-
369       significant unset bits in the mask value, and the result will  be  used
370       as  a the tin number for that packet.  This can be used to set policies
371       in a firewall script that will override CAKE's built-in tin selection.
372
373

OTHER PARAMETERS

375       memlimit LIMIT
376            Limit the memory consumed by Cake to LIMIT bytes. Note  that  this
377       does not translate directly to queue size (so do not size this based on
378       bandwidth delay  product  considerations,  but  rather  on  worst  case
379       acceptable  memory  consumption), as there is some overhead in the data
380       structures containing the packets, especially for small packets.
381
382            By default, the limit is calculated based on the bandwidth and RTT
383       settings.
384
385
386       wash
387
388            Traffic  entering your diffserv domain is frequently mis-marked in
389       transit from the perspective of your network, and traffic exiting yours
390       may be mis-marked from the perspective of the transiting provider.
391
392       Apply  the  wash option to clear all extra diffserv (but not ECN bits),
393       after priority queuing has taken place.
394
395       If you are shaping inbound, and cannot trust the diffserv markings  (as
396       is  the case for Comcast Cable, among others), it is best to use a sin‐
397       gle queue "besteffort" mode with wash.
398
399
400       split-gso
401
402            This option controls whether CAKE will split General  Segmentation
403       Offload  (GSO)  super-packets  into  their  on-the-wire  components and
404       dequeue them individually.
405
406       Super-packets are created by the  networking  stack  to  improve  effi‐
407       ciency.   However, because they are larger they take longer to dequeue,
408       which translates to higher latency for competing flows,  especially  at
409       lower bandwidths. CAKE defaults to splitting GSO packets to achieve the
410       lowest possible latency. At link speeds higher than  10  Gbps,  setting
411       the no-split-gso parameter can increase the maximum achievable through‐
412       put by retaining the full GSO packets.
413
414

OVERRIDING CLASSIFICATION WITH TC FILTERS

416       CAKE supports overriding of  its  internal  classification  of  packets
417       through  the  tc filter mechanism. Packets can be assigned to different
418       priority tins by setting the priority field on the skb,  and  the  flow
419       hashing can be overridden by setting the classid parameter.
420
421
422       Tin override
423
424               To  assign  a  priority  tin,  the major number of the priority
425       field needs to match the qdisc handle of the cake instance; if it does,
426       the  minor number will be interpreted as the tin index. For example, to
427       classify all ICMP packets as 'bulk', the following filter can be used:
428
429               # tc qdisc replace dev eth0 handle 1: root cake diffserv3
430               # tc filter add dev eth0 parent 1: protocol ip prio 1 \
431                 u32 match icmp type 0 0 action skbedit priority 1:1
432
433
434       Flow hash override
435
436               To override flow hashing, the classid can  be  set.  CAKE  will
437       interpret the major number of the classid as the host hash used in host
438       isolation mode, and the minor number as the flow hash  used  for  flow-
439       based  queueing.  One  or both of those can be set, and will be used if
440       the relevant flow isolation parameter is set (i.e.,  the  major  number
441       will  be ignored if CAKE is not configured in hosts mode, and the minor
442       number will be ignored if CAKE is not configured in flows mode).
443
444       This example will assign all ICMP packets to the first queue:
445
446               # tc qdisc replace dev eth0 handle 1: root cake
447               # tc filter add dev eth0 parent 1: protocol ip prio 1 \
448                 u32 match icmp type 0 0 classid 0:1
449
450       If only one of the host and flow overrides is set,  CAKE  will  compute
451       the  other hash from the packet as normal. Note, however, that the host
452       isolation mode works by assigning a host ID to the flow  queue;  so  if
453       overriding  both host and flow, the same flow cannot have more than one
454       host assigned. In addition, it is  not  possible  to  assign  different
455       source  and  destination  host IDs through the override mechanism; if a
456       host ID is assigned, it will be used as  both  source  and  destination
457       host.
458
459
460
461

EXAMPLES

463       # tc qdisc delete root dev eth0
464       # tc qdisc add root dev eth0 cake bandwidth 100Mbit ethernet
465       # tc -s qdisc show dev eth0
466       qdisc  cake 1: root refcnt 2 bandwidth 100Mbit diffserv3 triple-isolate
467       rtt 100.0ms noatm overhead 38 mpu 84
468        Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
469        backlog 0b 0p requeues 0
470        memory used: 0b of 5000000b
471        capacity estimate: 100Mbit
472        min/max network layer size:        65535 /       0
473        min/max overhead-adjusted size:    65535 /       0
474        average network hdr offset:            0
475
476                          Bulk  Best Effort        Voice
477         thresh       6250Kbit      100Mbit       25Mbit
478         target          5.0ms        5.0ms        5.0ms
479         interval      100.0ms      100.0ms      100.0ms
480         pk_delay          0us          0us          0us
481         av_delay          0us          0us          0us
482         sp_delay          0us          0us          0us
483         pkts                0            0            0
484         bytes               0            0            0
485         way_inds            0            0            0
486         way_miss            0            0            0
487         way_cols            0            0            0
488         drops               0            0            0
489         marks               0            0            0
490         ack_drop            0            0            0
491         sp_flows            0            0            0
492         bk_flows            0            0            0
493         un_flows            0            0            0
494         max_len             0            0            0
495         quantum           300         1514          762
496
497       After some use:
498       # tc -s qdisc show dev eth0
499
500       qdisc cake 1: root refcnt 2 bandwidth 100Mbit diffserv3  triple-isolate
501       rtt 100.0ms noatm overhead 38 mpu 84
502        Sent  44709231  bytes 31931 pkt (dropped 45, overlimits 93782 requeues
503       0)
504        backlog 33308b 22p requeues 0
505        memory used: 292352b of 5000000b
506        capacity estimate: 100Mbit
507        min/max network layer size:           28 /    1500
508        min/max overhead-adjusted size:       84 /    1538
509        average network hdr offset:           14
510
511                          Bulk  Best Effort        Voice
512         thresh       6250Kbit      100Mbit       25Mbit
513         target          5.0ms        5.0ms        5.0ms
514         interval      100.0ms      100.0ms      100.0ms
515         pk_delay        8.7ms        6.9ms        5.0ms
516         av_delay        4.9ms        5.3ms        3.8ms
517         sp_delay        727us        1.4ms        511us
518         pkts             2590        21271         8137
519         bytes         3081804     30302659     11426206
520         way_inds            0           46            0
521         way_miss            3           17            4
522         way_cols            0            0            0
523         drops              20           15           10
524         marks               0            0            0
525         ack_drop            0            0            0
526         sp_flows            2            4            1
527         bk_flows            1            2            1
528         un_flows            0            0            0
529         max_len          1514         1514         1514
530         quantum           300         1514          762
531
532

SEE ALSO

534       tc(8), tc-codel(8), tc-fq_codel(8), tc-htb(8)
535
536

AUTHORS

538       Cake's principal author is Jonathan  Morton,  with  contributions  from
539       Tony  Ambardar, Kevin Darbyshire-Bryant, Toke Høiland-Jørgensen, Sebas‐
540       tian Moeller, Ryan Mounce, Dean Scarff, Nils  Andreas  Svee,  and  Dave
541       Täht.
542
543       This  manual  page  was  written by Loganaden Velvindron. Please report
544       corrections to the  Linux  Networking  mailing  list  <netdev@vger.ker‐
545       nel.org>.
546
547
548
549iproute2                         19 July 2018                          CAKE(8)
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