man/man8/tc-htb.8

   1 .TH HTB 8 "10 January 2002" "iproute2" "Linux"
   2 .SH NAME
   3 HTB \- Hierarchy Token Bucket
   4 .SH SYNOPSIS
   5 .B tc qdisc ... dev
   6 dev
   7 .B  ( parent
   8 classid
   9 .B | root) [ handle
  10 major:
  11 .B ] htb [ default
  12 minor-id
  13 .B ]
  14
  15 .B tc class ... dev
  16 dev
  17 .B parent
  18 major:[minor]
  19 .B [ classid
  20 major:minor
  21 .B ] htb rate
  22 rate
  23 .B [ ceil
  24 rate
  25 .B ] burst
  26 bytes
  27 .B [ cburst
  28 bytes
  29 .B ] [ prio
  30 priority
  31 .B ]
  32
  33 .SH DESCRIPTION
  34 HTB is meant as a more understandable and intuitive replacement for
  35 the CBQ qdisc in Linux. Both CBQ and HTB help you to control the use
  36 of the outbound bandwidth on a given link. Both allow you to use one
  37 physical link to simulate several slower links and to send different
  38 kinds of traffic on different simulated links. In both cases, you have
  39 to specify how to divide the physical link into simulated links and
  40 how to decide which simulated link to use for a given packet to be sent.
  41
  42 Unlike CBQ, HTB shapes traffic based on the Token Bucket Filter algorithm
  43 which does not depend on interface characteristics and so does not need to
  44 know the underlying bandwidth of the outgoing interface.
  45
  46 .SH SHAPING ALGORITHM
  47 Shaping works as documented in
  48 .B tc-tbf (8).
  49
  50 .SH CLASSIFICATION
  51 Within the one HRB instance many classes may exist. Each of these classes
  52 contains another qdisc, by default
  53 .BR tc-pfifo (8).
  54
  55 When enqueueing a packet, HTB starts at the root and uses various methods to
  56 determine which class should receive the data.
  57
  58 In the absence of uncommon configuration options, the process is rather easy.
  59 At each node we look for an instruction, and then go to the class the
  60 instruction refers us to. If the class found is a barren leaf-node (without
  61 children), we enqueue the packet there. If it is not yet a leaf node, we do
  62 the whole thing over again starting from that node.
  63
  64 The following actions are performed, in order at each node we visit, until one
  65 sends us to another node, or terminates the process.
  66 .TP
  67 (i)
  68 Consult filters attached to the class. If sent to a leafnode, we are done.
  69 Otherwise, restart.
  70 .TP
  71 (ii)
  72 If none of the above returned with an instruction, enqueue at this node.
  73 .P
  74 This algorithm makes sure that a packet always ends up somewhere, even while
  75 you are busy building your configuration.
  76
  77 .SH LINK SHARING ALGORITHM
  78 FIXME
  79
  80 .SH QDISC
  81 The root of a HTB qdisc class tree has the following parameters:
  82
  83 .TP
  84 parent major:minor | root
  85 This mandatory parameter determines the place of the HTB instance, either at the
  86 .B root
  87 of an interface or within an existing class.
  88 .TP
  89 handle major:
  90 Like all other qdiscs, the HTB can be assigned a handle. Should consist only
  91 of a major number, followed by a colon. Optional, but very useful if classes
  92 will be generated within this qdisc.
  93 .TP
  94 default minor-id
  95 Unclassified traffic gets sent to the class with this minor-id.
  96
  97 .SH CLASSES
  98 Classes have a host of parameters to configure their operation.
  99
 100 .TP
 101 parent major:minor
 102 Place of this class within the hierarchy. If attached directly to a qdisc
 103 and not to another class, minor can be omitted. Mandatory.
 104 .TP
 105 classid major:minor
 106 Like qdiscs, classes can be named. The major number must be equal to the
 107 major number of the qdisc to which it belongs. Optional, but needed if this
 108 class is going to have children.
 109 .TP
 110 prio priority
 111 In the round-robin process, classes with the lowest priority field are tried
 112 for packets first. Mandatory.
 113
 114 .TP
 115 rate rate
 116 Maximum rate this class and all its children are guaranteed. Mandatory.
 117
 118 .TP
 119 ceil rate
 120 Maximum rate at which a class can send, if its parent has bandwidth to spare.
 121 Defaults to the configured rate, which implies no borrowing
 122
 123 .TP
 124 burst bytes
 125 Amount of bytes that can be burst at
 126 .B ceil
 127 speed, in excess of the configured
 128 .B rate.
 129 Should be at least as high as the highest burst of all children.
 130
 131 .TP
 132 cburst bytes
 133 Amount of bytes that can be burst at 'infinite' speed, in other words, as fast
 134 as the interface can transmit them. For perfect evening out, should be equal to at most one average
 135 packet. Should be at least as high as the highest cburst of all children.
 136
 137 .SH NOTES
 138 Due to Unix timing constraints, the maximum ceil rate is not infinite and may in fact be quite low. On Intel,
 139 there are 100 timer events per second, the maximum rate is that rate at which 'burst' bytes are sent each timer tick.
 140 From this, the minimum burst size for a specified rate can be calculated. For i386, a 10mbit rate requires a 12 kilobyte
 141 burst as 100*12kb*8 equals 10mbit.
 142
 143 .SH SEE ALSO
 144 .BR tc (8)
 145 .P
 146 HTB website: http://luxik.cdi.cz/~devik/qos/htb/
 147 .SH AUTHOR
 148 Martin Devera <devik@cdi.cz>. This manpage maintained by bert hubert <ahu@ds9a.nl>
 149
 150