HTB(8)                                                         Linux                                                         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 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 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.


       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.

       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 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  be‐
              longs. 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 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 at which 'burst' bytes are sent each timer tick.  From this, the min‐
       imum 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 <>. This manpage maintained by bert hubert <>

iproute2                                                  10 January 2002                                                    HTB(8)