tc-htb(8) — Linux manual page


HTB(8)                              Linux                             HTB(8)

NAME         top

       HTB - Hierarchy Token Bucket

SYNOPSIS         top

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

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

DESCRIPTION         top

       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


       Shaping works as documented in tc-tbf(8).


       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.



QDISC         top

       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-

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

CLASSES         top

       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.

       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.

       rate rate
              Maximum rate this class and all its children are guaranteed.

       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.

       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 ignored.

NOTES         top

       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         top


       HTB website:

AUTHOR         top

       Martin Devera <>. This manpage maintained by bert hubert

COLOPHON         top

       This page is part of the iproute2 (utilities for controlling TCP/IP
       networking and traffic) project.  Information about the project can
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iproute2                       10 January 2002                        HTB(8)

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