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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 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 con‐
       figuration.


LINK SHARING ALGORITHM
       FIXME


QDISC
       The root of a HTB qdisc class tree has the following parameters:



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 <[email protected]>. This manpage maintained by bert hubert <[email protected]>