Provided by: iproute_20041019-4ubuntu5_i386 bug

NAME

       HTB - Hierarchy Token Bucket

SYNOPSIS

       tc  qdisc  ... dev dev ( parent classid | root) [ handle major: ] htb [
       default minor-id ]

       tc class ... dev dev parent major:[minor] [ classid major:minor  ]  htb
       rate rate [ ceil rate ] burst bytes [ cburst bytes ] [ prio priority ]

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
       specify 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
       algorithm 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 HRB 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
       methods 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
              existing 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.

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. Mandatory.

       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
              bandwidth 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
              children.

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 mininum 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@cdi.cz>. This manpage maintained  by  bert  hubert
       <ahu@ds9a.nl>