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>