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 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 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 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  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 <devikATcdi.cz>. This manpage maintained by bert hubert <ahuATds9a.nl>





iproute2                                                 10 January 2002                                                  HTB(8)