tc-htb(8) - man - phpMan

HTB(8)                                          Linux                                         HTB(8)



NAME
       HTB - Hierarchy Token Bucket

SYNOPSIS
       tc  qdisc  ...  dev dev ( parent classid | root) [ handle major: ] htb [ default minor-id ] [
       r2q divisor ] [ offload ]

       tc class ... dev dev parent major:[minor] [ classid major:minor ] htb rate rate [ ceil rate ]
       burst bytes [ cburst bytes ] [ prio priority ] [ quantum bytes ]


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  di‐
       vide 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  de‐
       pend  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 ma‐
              jor number, followed by a colon. Optional, but very useful if classes will  be  gener‐
              ated within this qdisc.

       default minor-id
              Unclassified traffic gets sent to the class with this minor-id.

       r2q divisor
              Divisor  used  to  calculate  quantum values for classes.  Classes divide rate by this
              number.  Default value is 10.

       offload
              Offload the HTB algorithm to hardware (requires driver and device support).


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 pack‐
              ets first.


       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.   De‐
              faults 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.


       quantum bytes
              Number of bytes to serve from this class before the scheduler moves to the next class.
              Default  value  is  rate divided by the qdisc r2q parameter.  If specified, r2q is ig‐
              nored.


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 AT cdi.cz>. This manpage maintained by bert hubert <ahu AT ds9a.nl>



iproute2                                   10 January 2002                                    HTB(8)