Linux offers a very rich set of tools for managing and manipulating the transmission of packets. The larger Linux community is very familiar with the tools available under Linux for packet mangling and firewalling (netfilter, and before that, ipchains) as well as hundreds of network services which can run on the operating system. Few inside the community and fewer outside the Linux community are aware of the tremendous power of the traffic control subsystem which has grown and matured under kernels 2.2 and 2.4.
This HOWTO purports to introduce the concepts of traffic control, the traditional elements (in general), the components of the Linux traffic control implementation and provide some guidelines . This HOWTO represents the collection, amalgamation and synthesis of the LARTC HOWTO, documentation from individual projects and importantly the LARTC mailing list over a period of study.
The impatient soul, who simply wishes to experiment right now, is recommended to the Traffic Control using tcng and HTB HOWTO and LARTC HOWTO for immediate satisfaction.
The target audience for this HOWTO is the network administrator or savvy home user who desires an introduction to the field of traffic control and an overview of the tools available under Linux for implementing traffic control.
I assume that the reader is comfortable with UNIX concepts and the command line and has a basic knowledge of IP networking. Users who wish to implement traffic control may require the ability to patch, compile and install a kernel or software package [1]. For users with newer kernels (2.4.20+, see also Section 5.1, “Kernel requirements”), however, the ability to install and use software may be all that is required.
Broadly speaking, this HOWTO was written with a sophisticated user in mind, perhaps one who has already had experience with traffic control under Linux. I assume that the reader may have no prior traffic control experience.
This text was written in DocBook (version 4.2) with vim. All formatting has been applied by xsltproc based on DocBook XSL and LDP XSL stylesheets. Typeface formatting and display conventions are similar to most printed and electronically distributed technical documentation.
I strongly recommend to the eager reader making a first foray into the discipline of traffic control, to become only casually familiar with the tc command line utility, before concentrating on tcng. The tcng software package defines an entire language for describing traffic control structures. At first, this language may seem daunting, but mastery of these basics will quickly provide the user with a much wider ability to employ (and deploy) traffic control configurations than the direct use of tc would afford.
Where possible, I'll try to prefer describing the behaviour of the Linux traffic control system in an abstract manner, although in many cases I'll need to supply the syntax of one or the other common systems for defining these structures. I may not supply examples in both the tcng language and the tc command line, so the wise user will have some familiarity with both.
There is content yet missing from this HOWTO. In particular, the following items will be added at some point to this documentation.
A description and diagram of GRED, WRR, PRIO and CBQ.
A section of examples.
A section detailing the classifiers.
A section discussing the techniques for measuring traffic.
A section covering meters.
More details on tcng.
I welcome suggestions, corrections and feedback at <martin@linux-ip.net>. All errors
and omissions are strictly my fault. Although I have made every effort
to verify the factual correctness of the content presented herein, I
cannot accept any responsibility for actions taken under the influence
of this documentation.
[1] See Section 5, “Software and Tools” for more details on the use or installation of a particular traffic control mechanism, kernel or command line utility.