tc qdisc … dev
| root) [ handle
] htb [ default
tc class … dev
] htb rate
] [ prio
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
Within the one HRB 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 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.
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:
of an interface or within an existing class.
Classes have a host of parameters to configure their operation.
speed, in excess of the configured
Should be at least as high as the highest burst of all children.
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.
HTB website: http://luxik.cdi.cz/~devik/qos/htb/