tc-htb

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  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 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	 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 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.


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)