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 ] [ 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         top

       HTB allows  control of the outbound bandwidth on a given link.
       It allows simulating simulating 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.

       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

       (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

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

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

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. 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.

       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.

       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

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

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 be found at 
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iproute2                     10 January 2002                      HTB(8)

Pages that refer to this page: tc(8)tc-cake(8)tc-drr(8)tc-pedit(8)