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 allows  control of the outbound bandwidth on a given link.  It
       allows simulating 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.

       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 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
       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.

       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
	      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.


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

iproute2			10 January 2002				HTB(8)