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HTB(8)                               Linux                              HTB(8)
NAME
       HTB - Hierarchy Token Bucket
SYNOPSIS
       tc  qdisc  ... dev dev ( parent classid | root) [ handle major: ] htb [
       default minor-id ] [ r2q divisor ] [ offload ]
       tc class ... dev dev parent major:[minor] [ classid major:minor  ]  htb
       rate  rate [ ceil rate ] burst bytes [ cburst bytes ] [ prio priority ]
       [ quantum bytes ]
DESCRIPTION
       HTB is meant as a more understandable and intuitive replacement for the
       CBQ qdisc in Linux. Both CBQ and HTB help you to control the use of the
       outbound bandwidth on a given link. Both allow you to use one  physical
       link  to  simulate  several slower links and to send different kinds of
       traffic on different simulated links. In both cases, you have to  spec-
       ify  how  to  divide  the physical link into simulated links and how to
       decide which simulated link to use for a given packet to be sent.
       Unlike CBQ, HTB shapes traffic based on the Token Bucket  Filter  algo-
       rithm  which  does  not depend on interface characteristics and so does
       not need to know the underlying bandwidth of the outgoing interface.
SHAPING ALGORITHM
       Shaping works as documented in tc-tbf (8).
CLASSIFICATION
       Within the one HTB instance many  classes  may  exist.  Each  of  these
       classes contains another qdisc, by default tc-pfifo(8).
       When enqueueing a packet, HTB starts at the root and uses various meth-
       ods to determine which class should receive the data.
       In the absence of uncommon configuration options, the process is rather
       easy.   At  each  node  we  look for an instruction, and then go to the
       class the instruction refers us to. If the  class  found  is  a  barren
       leaf-node (without children), we enqueue the packet there. If it is not
       yet a leaf node, we do the whole thing over again  starting  from  that
       node.
       The  following  actions  are performed, in order at each node we visit,
       until one sends us to another node, or terminates the process.
       (i)    Consult filters attached to the class. If sent to a leafnode, we
              are done.  Otherwise, restart.
       (ii)   If  none  of  the above returned with an instruction, enqueue at
              this node.
       This algorithm makes sure that a packet always ends up somewhere,  even
       while you are busy building your configuration.
LINK SHARING ALGORITHM
       FIXME
QDISC
       The root of a HTB qdisc class tree has the following parameters:
       parent major:minor | root
              This  mandatory  parameter  determines  the  place  of  the  HTB
              instance, either at the root of an interface or within an exist-
              ing class.
       handle major:
              Like  all other qdiscs, the HTB can be assigned a handle. Should
              consist only of a major number, followed by a  colon.  Optional,
              but very useful if classes will be generated within this qdisc.
       default minor-id
              Unclassified traffic gets sent to the class with this minor-id.
       r2q divisor
              Divisor  used  to calculate quantum values for classes.  Classes
              divide rate by this number.  Default value is 10.
       offload
              Offload the HTB  algorithm  to  hardware  (requires  driver  and
              device support).
CLASSES
       Classes have a host of parameters to configure their operation.
       parent major:minor
              Place  of  this class within the hierarchy. If attached directly
              to a qdisc and not to  another  class,  minor  can  be  omitted.
              Mandatory.
       classid major:minor
              Like  qdiscs,  classes  can  be  named. The major number must be
              equal to the major number of the  qdisc  to  which  it  belongs.
              Optional, but needed if this class is going to have children.
       prio priority
              In  the  round-robin  process,  classes with the lowest priority
              field are tried for packets first.
       rate rate
              Maximum rate this class and all  its  children  are  guaranteed.
              Mandatory.
       ceil rate
              Maximum  rate at which a class can send, if its parent has band-
              width to spare.  Defaults to the configured rate, which  implies
              no borrowing
       burst bytes
              Amount  of  bytes  that can be burst at ceil speed, in excess of
              the configured rate.  Should be at least as high as the  highest
              burst of all children.
       cburst bytes
              Amount  of bytes that can be burst at 'infinite' speed, in other
              words, as fast as the interface can transmit them.  For  perfect
              evening  out,  should  be  equal  to at most one average packet.
              Should be at least as high as the highest cburst  of  all  chil-
              dren.
       quantum bytes
              Number  of  bytes  to serve from this class before the scheduler
              moves to the next class.  Default value is rate divided  by  the
              qdisc r2q parameter.  If specified, r2q is ignored.
NOTES
       Due  to  Unix timing constraints, the maximum ceil rate is not infinite
       and may in fact be quite low. On Intel, there are 100 timer events  per
       second,  the  maximum rate is that rate at which 'burst' bytes are sent
       each timer tick.  From this, the minimum burst  size  for  a  specified
       rate  can be calculated. For i386, a 10mbit rate requires a 12 kilobyte
       burst as 100*12kb*8 equals 10mbit.
SEE ALSO
       tc(8)
       HTB website: http://luxik.cdi.cz/~devik/qos/htb/
AUTHOR
       Martin Devera <devik AT cdi.cz>. This manpage maintained  by  bert  hubert
       <ahu AT ds9a.nl>
iproute2                        10 January 2002                         HTB(8)