Manual: tc-htb

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 allows  control of the outbound bandwidth on a given link.  It allows 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  physi‐
       cal 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 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 instruc‐
       tion, and then go to the class the instruction refers us to. If the class found is a barren leaf-node (without  chil‐
       dren), 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 termi‐
       nates 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  configura‐
       tion.

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 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
	      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 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.

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 specified 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 . This manpage maintained by bert hubert 

iproute2					       10 January 2002						      HTB(8)