--- /dev/null
+.TH TC 8 "16 December 2001" "iproute2" "Linux"
+.SH NAME
+tc \- show / manipulate traffic control settings
+.SH SYNOPSIS
+.B tc qdisc [ add | change | replace | link ] dev
+DEV
+.B
+[ parent
+qdisc-id
+.B | root ]
+.B [ handle
+qdisc-id ] qdisc
+[ qdisc specific parameters ]
+.P
+
+.B tc class [ add | change | replace ] dev
+DEV
+.B parent
+qdisc-id
+.B [ classid
+class-id ] qdisc
+[ qdisc specific parameters ]
+.P
+
+.B tc filter [ add | change | replace ] dev
+DEV
+.B [ parent
+qdisc-id
+.B | root ] protocol
+protocol
+.B prio
+priority filtertype
+[ filtertype specific parameters ]
+.B flowid
+flow-id
+
+.B tc [-s | -d ] qdisc show [ dev
+DEV
+.B ]
+.P
+.B tc [-s | -d ] class show dev
+DEV
+.P
+.B tc filter show dev
+DEV
+
+.SH DESCRIPTION
+.B Tc
+is used to configure Traffic Control in the Linux kernel. Traffic Control consists
+of the following:
+
+.TP
+SHAPING
+When traffic is shaped, its rate of transmission is under control. Shaping may
+be more than lowering the available bandwidth - it is also used to smooth out
+bursts in traffic for better network behaviour. Shaping occurs on egress.
+
+.TP
+SCHEDULING
+By scheduling the transmission of packets it is possible to improve interactivity
+for traffic that needs it while still guaranteeing bandwidth to bulk transfers. Reordering
+is also called prioritizing, and happens only on egress.
+
+.TP
+POLICING
+Where shaping deals with transmission of traffic, policing pertains to traffic
+arriving. Policing thus occurs on ingress.
+
+.TP
+DROPPING
+Traffic exceeding a set bandwidth may also be dropped forthwith, both on
+ingress and on egress.
+
+.P
+Processing of traffic is controlled by three kinds of objects: qdiscs,
+classes and filters.
+
+.SH QDISCS
+.B qdisc
+is short for 'queueing discipline' and it is elementary to
+understanding traffic control. Whenever the kernel needs to send a
+packet to an interface, it is
+.B enqueued
+to the qdisc configured for that interface. Immediately afterwards, the kernel
+tries to get as many packets as possible from the qdisc, for giving them
+to the network adaptor driver.
+
+A simple QDISC is the 'pfifo' one, which does no processing at all and is a pure
+First In, First Out queue. It does however store traffic when the network interface
+can't handle it momentarily.
+
+.SH CLASSES
+Some qdiscs can contain classes, which contain further qdiscs - traffic may
+then be enqueued in any of the inner qdiscs, which are within the
+.B classes.
+When the kernel tries to dequeue a packet from such a
+.B classful qdisc
+it can come from any of the classes. A qdisc may for example prioritize
+certain kinds of traffic by trying to dequeue from certain classes
+before others.
+
+.SH FILTERS
+A
+.B filter
+is used by a classful qdisc to determine in which class a packet will
+be enqueued. Whenever traffic arrives at a class with subclasses, it needs
+to be classified. Various methods may be employed to do so, one of these
+are the filters. All filters attached to the class are called, until one of
+them returns with a verdict. If no verdict was made, other criteria may be
+available. This differs per qdisc.
+
+It is important to notice that filters reside
+.B within
+qdiscs - they are not masters of what happens.
+
+.SH CLASSLESS QDISCS
+The classless qdiscs are:
+.TP
+[p|b]fifo
+Simplest usable qdisc, pure First In, First Out behaviour. Limited in
+packets or in bytes.
+.TP
+pfifo_fast
+Standard qdisc for 'Advanced Router' enabled kernels. Consists of a three-band
+queue which honors Type of Service flags, as well as the priority that may be
+assigned to a packet.
+.TP
+red
+Random Early Detection simulates physical congestion by randomly dropping
+packets when nearing configured bandwidth allocation. Well suited to very
+large bandwidth applications.
+.TP
+sfq
+Stochastic Fairness Queueing reorders queued traffic so each 'session'
+gets to send a packet in turn.
+.TP
+tbf
+The Token Bucket Filter is suited for slowing traffic down to a precisely
+configured rate. Scales well to large bandwidths.
+.SH CONFIGURING CLASSLESS QDISCS
+In the absence of classful qdiscs, classless qdiscs can only be attached at
+the root of a device. Full syntax:
+.P
+.B tc qdisc add dev
+DEV
+.B root
+QDISC QDISC-PARAMETERS
+
+To remove, issue
+.P
+.B tc qdisc del dev
+DEV
+.B root
+
+The
+.B pfifo_fast
+qdisc is the automatic default in the absence of a configured qdisc.
+
+.SH CLASSFUL QDISCS
+The classful qdiscs are:
+.TP
+CBQ
+Class Based Queueing implements a rich linksharing hierarchy of classes.
+It contains shaping elements as well as prioritizing capabilities. Shaping is
+performed using link idle time calculations based on average packet size and
+underlying link bandwidth. The latter may be ill-defined for some interfaces.
+.TP
+HTB
+The Hierarchy Token Bucket implements a rich linksharing hierarchy of
+classes with an emphasis on conforming to existing practices. HTB facilitates
+guaranteeing bandwidth to classes, while also allowing specification of upper
+limits to inter-class sharing. It contains shaping elements, based on TBF and
+can prioritize classes.
+.TP
+PRIO
+The PRIO qdisc is a non-shaping container for a configurable number of
+classes which are dequeued in order. This allows for easy prioritization
+of traffic, where lower classes are only able to send if higher ones have
+no packets available. To facilitate configuration, Type Of Service bits are
+honored by default.
+.SH THEORY OF OPERATION
+Classes form a tree, where each class has a single parent.
+A class may have multiple children. Some qdiscs allow for runtime addition
+of classes (CBQ, HTB) while others (PRIO) are created with a static number of
+children.
+
+Qdiscs which allow dynamic addition of classes can have zero or more
+subclasses to which traffic may be enqueued.
+
+Furthermore, each class contains a
+.B leaf qdisc
+which by default has
+.B pfifo
+behaviour though another qdisc can be attached in place. This qdisc may again
+contain classes, but each class can have only one leaf qdisc.
+
+When a packet enters a classful qdisc it can be
+.B classified
+to one of the classes within. Three criteria are available, although not all
+qdiscs will use all three:
+.TP
+tc filters
+If tc filters are attached to a class, they are consulted first
+for relevant instructions. Filters can match on all fields of a packet header,
+as well as on the firewall mark applied by ipchains or iptables. See
+.BR tc-filters (8).
+.TP
+Type of Service
+Some qdiscs have built in rules for classifying packets based on the TOS field.
+.TP
+skb->priority
+Userspace programs can encode a class-id in the 'skb->priority' field using
+the SO_PRIORITY option.
+.P
+Each node within the tree can have its own filters but higher level filters
+may also point directly to lower classes.
+
+If classification did not succeed, packets are enqueued to the leaf qdisc
+attached to that class. Check qdisc specific manpages for details, however.
+
+.SH NAMING
+All qdiscs, classes and filters have IDs, which can either be specified
+or be automatically assigned.
+
+IDs consist of a major number and a minor number, separated by a colon.
+
+.TP
+QDISCS
+A qdisc, which potentially can have children,
+gets assigned a major number, called a 'handle', leaving the minor
+number namespace available for classes. The handle is expressed as '10:'.
+It is customary to explicitly assign a handle to qdiscs expected to have
+children.
+
+.TP
+CLASSES
+Classes residing under a qdisc share their qdisc major number, but each have
+a separate minor number called a 'classid' that has no relation to their
+parent classes, only to their parent qdisc. The same naming custom as for
+qdiscs applies.
+
+.TP
+FILTERS
+Filters have a three part ID, which is only needed when using a hashed
+filter hierarchy, for which see
+.BR tc-filters (8).
+.SH UNITS
+All parameters accept a floating point number, possibly followed by a unit.
+.P
+Bandwidths or rates can be specified in:
+.TP
+kbps
+Kilobytes per second
+.TP
+mbps
+Megabytes per second
+.TP
+kbit
+Kilobits per second
+.TP
+mbit
+Megabits per second
+.TP
+bps or a bare number
+Bytes per second
+.P
+Amounts of data can be specified in:
+.TP
+kb or k
+Kilobytes
+.TP
+mb or m
+Megabytes
+.TP
+mbit
+Megabits
+.TP
+kbit
+Kilobits
+.TP
+b or a bare number
+Bytes.
+.P
+Lengths of time can be specified in:
+.TP
+s, sec or secs
+Whole seconds
+.TP
+ms, msec or msecs
+Milliseconds
+.TP
+us, usec, usecs or a bare number
+Microseconds.
+
+.SH TC COMMANDS
+The following commands are available for qdiscs, classes and filter:
+.TP
+add
+Add a qdisc, class or filter to a node. For all entities, a
+.B parent
+must be passed, either by passing its ID or by attaching directly to the root of a device.
+When creating a qdisc or a filter, it can be named with the
+.B handle
+parameter. A class is named with the
+.B classid
+parameter.
+
+.TP
+remove
+A qdisc can be removed by specifying its handle, which may also be 'root'. All subclasses and their leaf qdiscs
+are automatically deleted, as well as any filters attached to them.
+
+.TP
+change
+Some entities can be modified 'in place'. Shares the syntax of 'add', with the exception
+that the handle cannot be changed and neither can the parent. In other words,
+.B
+change
+cannot move a node.
+
+.TP
+replace
+Performs a nearly atomic remove/add on an existing node id. If the node does not exist yet
+it is created.
+
+.TP
+link
+Only available for qdiscs and performs a replace where the node
+must exist already.
+
+
+.SH HISTORY
+.B tc
+was written by Alexey N. Kuznetsov and added in Linux 2.2.
+.SH SEE ALSO
+.BR tc-cbq (8),
+.BR tc-htb (8),
+.BR tc-sfq (8),
+.BR tc-red (8),
+.BR tc-tbf (8),
+.BR tc-pfifo (8),
+.BR tc-bfifo (8),
+.BR tc-pfifo_fast (8),
+.BR tc-filters (8)
+
+.SH AUTHOR
+Manpage maintained by bert hubert (ahu@ds9a.nl)
+
git://git.onelab.eu / iproute2.git / blobdiff