5.1. Kernel requirements

Many distributions provide kernels with modular or monolithic support for traffic control (Quality of Service). Custom kernels may not already provide support (modular or not) for the required features. If not, this is a very brief listing of the required kernel options.

The user who has little or no experience compiling a kernel is recommended to Kernel HOWTO. Experienced kernel compilers should be able to determine which of the below options apply to the desired configuration, after reading a bit more about traffic control and planning.

#
# QoS and/or fair queueing
#
CONFIG_NET_SCHED=y
CONFIG_NET_SCH_CBQ=m
CONFIG_NET_SCH_HTB=m
CONFIG_NET_SCH_CSZ=m
CONFIG_NET_SCH_PRIO=m
CONFIG_NET_SCH_RED=m
CONFIG_NET_SCH_SFQ=m
CONFIG_NET_SCH_TEQL=m
CONFIG_NET_SCH_TBF=m
CONFIG_NET_SCH_GRED=m
CONFIG_NET_SCH_DSMARK=m
CONFIG_NET_SCH_INGRESS=m
CONFIG_NET_QOS=y
CONFIG_NET_ESTIMATOR=y
CONFIG_NET_CLS=y
CONFIG_NET_CLS_TCINDEX=m
CONFIG_NET_CLS_ROUTE4=m
CONFIG_NET_CLS_ROUTE=y
CONFIG_NET_CLS_FW=m
CONFIG_NET_CLS_U32=m
CONFIG_NET_CLS_RSVP=m
CONFIG_NET_CLS_RSVP6=m
CONFIG_NET_CLS_POLICE=y
      

A kernel compiled with the above set of options will provide modular support for almost everything discussed in this documentation. The user may need to modprobe module before using a given feature. Again, the confused user is recommended to the Kernel HOWTO, as this document cannot adequately address questions about the use of the Linux kernel.

5.2. iproute2 tools (tc)

iproute2 is a suite of command line utilities which manipulate kernel structures for IP networking configuration on a machine. For technical documentation on these tools, see the iproute2 documentation and for a more expository discussion, the documentation at linux-ip.net. Of the tools in the iproute2 package, the binary tc is the only one used for traffic control. This HOWTO will ignore the other tools in the suite.

Because it interacts with the kernel to direct the creation, deletion and modification of traffic control structures, the tc binary needs to be compiled with support for all of the qdiscs you wish to use. In particular, the HTB qdisc is not supported yet in the upstream iproute2 package. See Section 7.1 for more information.

The tc tool performs all of the configuration of the kernel structures required to support traffic control. As a result of its many uses, the command syntax can be described (at best) as arcane. The utility takes as its first non-option argument one of three Linux traffic control components, qdisc, class or filter.

[root@leander]# tc
Usage: tc [ OPTIONS ] OBJECT { COMMAND | help }
where  OBJECT := { qdisc | class | filter }
       OPTIONS := { -s[tatistics] | -d[etails] | -r[aw] }
      

Each object accepts further and different options, and will be incompletely described and documented below. The hints in the examples below are designed to introduce the vagaries of tc command line syntax. For more examples, consult the LARTC HOWTO. For even better understanding, consult the kernel and iproute2 code.

[root@leander]# tc qdisc add    \ 
>                  dev eth0     \ 
>                  root         \ 
>                  handle 1:0   \ 
>                  htb            
      

Above was the simplest use of the tc utility for adding a queuing discipline to a device. Here's an example of the use of tc to add a class to an existing parent class.

[root@leander]# tc class add    \ 
>                  dev eth0     \ 
>                  parent 1:1   \ 
>                  classid 1:6  \ 
>                  htb          \ 
>                  rate 256kbit \ 
>                  ceil 512kbit   
      

[root@leander]# tc filter add               \ 
>                  dev eth0                 \ 
>                  parent 1:0               \ 
>                  protocol ip              \ 
>                  prio 5                   \ 
>                  u32                      \ 
>                  match ip port 22 0xffff  \ 
>                  match ip tos 0x10 0xff   \ 
>                  flowid 1:6               \ 
>                  police                   \ 
>                  rate 32000bps            \ (11)
>                  burst 10240              \ (12)
>                  mpu 0                    \ (13)
>                  action drop/continue       (14)
      

As evidenced above, the tc command line utility has an arcane and complex syntax, even for simple operations such as these examples show. It should come as no surprised to the reader that there exists an easier way to configure Linux traffic control. See the next section, Section 5.3.

5.3. tcng, Traffic Control Next Generation

FIXME; sing the praises of tcng. See also Traffic Control using tcng and HTB HOWTO and tcng documentation.

Traffic control next generation (hereafter, tcng) provides all of the power of traffic control under Linux with twenty percent of the headache.

5.4. IMQ, Intermediate Queuing device

FIXME; must discuss IMQ. See also Patrick McHardy's website on IMQ.