Provided by: iproute2_6.1.0-1ubuntu6_amd64 bug

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  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  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>