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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 simu-
       lated 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  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 config-
       uration.


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.  Manda-
              tory.


       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 config-
              ured 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)