HTB(8)                  (10 January 2002)                  HTB(8)

          HTB - Hierarchy Token Bucket

          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 ]

          HTB is meant as a more understandable and intuitive replace-
          ment 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 charac-
          teristics and so does not need to know the underlying band-
          width of the outgoing interface.

          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

          When enqueueing a packet, HTB starts at the root and uses
          various methods to determine which class should receive the

          In the absence of uncommon configuration options, the pro-
          cess is rather easy.  At each node we look for an instruc-
          tion, 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.

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          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 some-
          where, even while you are busy building your configuration.


          The root of a HTB qdisc class tree has the following parame-

          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 han-
               dle. 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

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

          Classes have a host of parameters to configure their opera-

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          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 guar-
               anteed. 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 ignored.

          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

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          at which 'burst' bytes are sent each timer tick.  From this,
          the minimum burst size for a specified rate can be calcu-
          lated. For i386, a 10mbit rate requires a 12 kilobyte burst
          as 100*12kb*8 equals 10mbit.


          HTB website:

          Martin Devera <>. This manpage maintained by
          bert hubert <>

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