How to set TOS bits on LINUX ethernet interface
 

How can I configure TOS bits ( or IP precendence bits) on an ethernet interface of linux (Red Hat) ?

Can I configure this on a per ethernet interface basis ?

Tnx.

To do that you need iptables. The table of TOS is the following:
HEXA BINAIRE DECIMAL SIGNIFICATION
0x10 1000 8 Minimize Delay
0x08 0100 4 Maximize throughput
0x04 0010 2 Maximize reliability
0x02 0001 1 Minimize monetary cost
0x00 0000 0 Normal

and here is an example of the rules to use to add TOS in packets:
iptables -A PREROUTING -t mangle -p tcp --sport ssh -j TOS --set-tos Minimize-Delay
iptables -A PREROUTING -t mangle -p tcp --sport ftp -j TOS --set-tos Minimize-Delay
iptables -A PREROUTING -t mangle -p tcp --sport ftp-data -j TOS --set-tos Maximize-Throughput

Hope this help you :)

Tnx for your reply

Are you sure I need iptables for that ?

There is no way doing it without IPtables ?

Maybe there's a way to do it without iptables but I don't know it... Each time I've done QoS on Linux I have used tools like iptable or tc.
Now another way is to do your own program to modify TOS bits in packets :)