Examining and modifying packets in userspace using Netfilter

Hi,

I wanted to know how I could look at IP packets (including header and payload) arriving at a Linux Box by redirecting them to a users level process.

I plan to modify the TCP and IP headers in the process before sending them on the wire again.
This is just an academic excercise and not a system admin problem.

I am looking for a solution with minimal amount of kernel programming or firewall configuration.

I have looked at Netfilter documents but none of them have specified an exact method telling me what to do.

Thanks.

- Akshay

read more on Netfilter package you can find the way to do it. all things you need to learn is how to write driver kernel module and hook function using netfilter, then you can do whatever you want to do. you also can read more about this at www.linuxjournal.com