How to deal with this?

[Leisheng Ji]

I want to write a module or just make some
change on the source code of Linux to add
some function on the network module. What
I want to add is to let my module check the
content of the incoming IP package and
do things like deleting, puting in stack,
redirecting to other machine.
I looked into ipchains,but cant find it
can look into the payload of packages. 
Is here someone deal with such things 
before or know it? pls give me some
clue.

Thanks.