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Under GNU General Public License
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HTB(8) Linux HTB(8)
NAME
HTB - Hierarchy Token Bucket
SYNOPSIS
tc qdisc ... dev dev ( parent classid | root) [ handle major: ] htb [ default
minor-id ]
tc class ... dev dev parent major:[minor] [ classid major:minor ] htb rate rate [
ceil rate ] burst bytes [ cburst bytes ] [ prio priority ]
DESCRIPTION
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 ALGORITHM
Shaping works as documented in tc-tbf (8).
CLASSIFICATION
Within the one HRB 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 deter-
mine 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.
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.
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. Mandatory.
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 high-
est cburst of all children.
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
mininum 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 <devik AT cdi.cz>. This manpage maintained by bert hubert <ahu AT ds9a.nl>
iproute2 10 January 2002 HTB(8)
Generated by $Id: phpMan.php,v 4.49 2006/02/26 13:18:18 chedong Exp $ Author: Che Dong
On Apache/1.3.37 (Unix) mod_throttle/3.1.2 FrontPage/5.0.2.2635 mod_psoft_traffic/0.2 mod_ssl/2.8.28 OpenSSL/0.9.8b
Under GNU General Public License
2008-12-01 15:14 @38.103.63.55 Crawled by CCBot/1.0 (+http://www.commoncrawl.org/bot.html)