tc-htb(8) - phpMan

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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 spec-
       ify 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.  Other-
              wise, 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 num-
              ber 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 <devik AT cdi.cz>. This manpage maintained by bert hubert <ahu AT ds9a.nl>



iproute2                                 10 January 2002                                   HTB(8)

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