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 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.

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  speci-
       fied 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>

iproute2                                                          10 January 2002                                                           HTB(8)