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

NAME

6       HTB - Hierarchy Token Bucket
7

SYNOPSIS

9       tc  qdisc  ... dev dev ( parent classid | root) [ handle major: ] htb [
10       default minor-id ] [ r2q divisor ]
11
12       tc class ... dev dev parent major:[minor] [ classid major:minor  ]  htb
13       rate  rate [ ceil rate ] burst bytes [ cburst bytes ] [ prio priority ]
14       [ quantum bytes ]
15
16

DESCRIPTION

18       HTB is meant as a more understandable and intuitive replacement for the
19       CBQ qdisc in Linux. Both CBQ and HTB help you to control the use of the
20       outbound bandwidth on a given link. Both allow you to use one  physical
21       link  to  simulate  several slower links and to send different kinds of
22       traffic on different simulated links. In both cases, you have to  spec‐
23       ify  how  to  divide  the physical link into simulated links and how to
24       decide which simulated link to use for a given packet to be sent.
25
26       Unlike CBQ, HTB shapes traffic based on the Token Bucket  Filter  algo‐
27       rithm  which  does  not depend on interface characteristics and so does
28       not need to know the underlying bandwidth of the outgoing interface.
29
30

SHAPING ALGORITHM

32       Shaping works as documented in tc-tbf (8).
33
34

CLASSIFICATION

36       Within the one HTB instance many  classes  may  exist.  Each  of  these
37       classes contains another qdisc, by default tc-pfifo(8).
38
39       When enqueueing a packet, HTB starts at the root and uses various meth‐
40       ods to determine which class should receive the data.
41
42       In the absence of uncommon configuration options, the process is rather
43       easy.   At  each  node  we  look for an instruction, and then go to the
44       class the instruction refers us to. If the  class  found  is  a  barren
45       leaf-node (without children), we enqueue the packet there. If it is not
46       yet a leaf node, we do the whole thing over again  starting  from  that
47       node.
48
49       The  following  actions  are performed, in order at each node we visit,
50       until one sends us to another node, or terminates the process.
51
52       (i)    Consult filters attached to the class. If sent to a leafnode, we
53              are done.  Otherwise, restart.
54
55       (ii)   If  none  of  the above returned with an instruction, enqueue at
56              this node.
57
58       This algorithm makes sure that a packet always ends up somewhere,  even
59       while you are busy building your configuration.
60
61
63       FIXME
64
65

QDISC

67       The root of a HTB qdisc class tree has the following parameters:
68
69
70       parent major:minor | root
71              This  mandatory  parameter  determines  the  place  of  the  HTB
72              instance, either at the root of an interface or within an exist‐
73              ing class.
74
75       handle major:
76              Like  all other qdiscs, the HTB can be assigned a handle. Should
77              consist only of a major number, followed by a  colon.  Optional,
78              but very useful if classes will be generated within this qdisc.
79
80       default minor-id
81              Unclassified traffic gets sent to the class with this minor-id.
82
83       r2q divisor
84              Divisor  used  to calculate quantum values for classes.  Classes
85              divide rate by this number.  Default value is 10.
86
87

CLASSES

89       Classes have a host of parameters to configure their operation.
90
91
92       parent major:minor
93              Place of this class within the hierarchy. If  attached  directly
94              to  a  qdisc  and  not  to  another class, minor can be omitted.
95              Mandatory.
96
97       classid major:minor
98              Like qdiscs, classes can be named.  The  major  number  must  be
99              equal  to  the  major  number  of the qdisc to which it belongs.
100              Optional, but needed if this class is going to have children.
101
102       prio priority
103              In the round-robin process, classes  with  the  lowest  priority
104              field are tried for packets first.
105
106
107       rate rate
108              Maximum  rate  this  class  and all its children are guaranteed.
109              Mandatory.
110
111
112       ceil rate
113              Maximum rate at which a class can send, if its parent has  band‐
114              width  to spare.  Defaults to the configured rate, which implies
115              no borrowing
116
117
118       burst bytes
119              Amount of bytes that can be burst at ceil speed,  in  excess  of
120              the  configured rate.  Should be at least as high as the highest
121              burst of all children.
122
123
124       cburst bytes
125              Amount of bytes that can be burst at 'infinite' speed, in  other
126              words,  as  fast as the interface can transmit them. For perfect
127              evening out, should be equal to  at  most  one  average  packet.
128              Should  be  at  least as high as the highest cburst of all chil‐
129              dren.
130
131
132       quantum bytes
133              Number of bytes to serve from this class  before  the  scheduler
134              moves  to  the next class.  Default value is rate divided by the
135              qdisc r2q parameter.  If specified, r2q is ignored.
136
137

NOTES

139       Due to Unix timing constraints, the maximum ceil rate is  not  infinite
140       and  may in fact be quite low. On Intel, there are 100 timer events per
141       second, the maximum rate is that rate at which 'burst' bytes  are  sent
142       each  timer  tick.   From  this, the minimum burst size for a specified
143       rate can be calculated. For i386, a 10mbit rate requires a 12  kilobyte
144       burst as 100*12kb*8 equals 10mbit.
145
146

SEE ALSO

148       tc(8)
149
150       HTB website: http://luxik.cdi.cz/~devik/qos/htb/
151

AUTHOR

153       Martin  Devera  <devik@cdi.cz>.  This manpage maintained by bert hubert
154       <ahu@ds9a.nl>
155
156
157
158iproute2                        10 January 2002                         HTB(8)
Impressum