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tc-htb.8.gz

HTB(8)                          Linux                         HTB(8)



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  replace‐
       ment 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  dif‐
       ferent  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 Fil‐
       ter algorithm which does not depend on interface characteris‐
       tics 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 some‐
       where, even while you are busy building your configuration.


LINK SHARING ALGORITHM
       FIXME


QDISC
       The root of a HTB qdisc class tree has the following  parame‐
       ters:


       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 han‐
              dle. 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 opera‐
       tion.


       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 guar‐
              anteed. 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>





iproute2                   10 January 2002                    HTB(8)
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