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 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.


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



iproute2			10 January 2002				HTB(8)