net_cls subsystem tags network packets with a class identifier (classid) that allows the Linux traffic controller (tc) to identify packets originating from a particular cgroup. The traffic controller can be configured to assign different priorities to packets from different cgroups.
net_cls.classid contains a single value that indicates a traffic control handle. The value of
classid read from the
net_cls.classid file is presented in the decimal format while the value to be written to the file is expected in the hexadecimal format. For example,
0x100001 represents the handle conventionally written as
10:1 in the format used by the ip utility. In the
net_cls.classid file, it would be represented by the number
The format for these handles is:
0xAAAABBBB, where AAAA is the major number in hexadecimal and BBBB is the minor number in hexadecimal. You can omit any leading zeroes;
0x10001 is the same as
0x00010001, and represents
1:1. The following is an example of setting a
10:1 handle in the
echo 0x100001 > /cgroup/net_cls/red/net_cls.classid
Refer to the man page for tc to learn how to configure the traffic controller to use the handles that the
net_cls adds to network packets.