[lug] Setting values in IP headers

[D. Stimits]

Budyanto Himawan wrote:

> Hi,
>
> Does anybody know if it's possible to change values to some fields
> in the IP headers (in particular the TOS field)? Is there a c function
> that can achieve this?
>
> I'm trying to see if I can control the TOS fields of ip packets going
> out of my linux box.
>
> Thanks

I can't tell you offhand which code it is, but definitely it is 
available. Probably though it requires the right kernel QoS features. 
There is currently traffic shaping software available, which does 
exactly this. It was around 2.4.19 when it became fully available I 
think, so older kernels may not support it. Here is a link to some 
software which has to have hooks into the kernel code which uses the 
same thing as you are interested in:
  http://tldp.org/HOWTO/Traffic-Control-tcng-HTB-HOWTO/

D. Stimits, stimits AT comcast DOT net