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HTB(8)                               Linux                              HTB(8)

       HTB - Hierarchy Token Bucket

       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 ]

       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 works as documented in tc-tbf (8).

       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 deter-
       mine 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.


       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 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 high-
              est cburst of all children.

       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.


       HTB website:

       Martin Devera <devik AT>. This manpage maintained by bert hubert <ahu AT>

iproute2                        10 January 2002                         HTB(8)

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