TCP/IP stack - doubts

I have a few basic questions regarding the TCP/IP stack.

1. Is this an integrated part of the kernel? As in, if I modify the IP layer do
I need to recompile the kernel?
2. If its an integrated part of the kernel, would it make sense to make each
layer
a module? so that whoever is experimenting with it can modify that layer and
just do an insmod.
3. I am planning to implement a strip down version of IPSec protocol as
suggested by Radia Perlman in her paper "Analysis of the IPSec Key Exchange
Protocol" any comments about that?


Thanks in advance!
- Amit Khandelwal