Prerequisites: A machine with Linux and a recent (preferably 2.4.20) kernel on it. The source for your kernel (http://www.mirror.ac.uk/sites/ftp.kernel.org/pub/linux/kernel/v2.4/linux-2.4.20.tar.bz2 is the one I am using). A recent FreeS/WAN archive (the FreeS/WAN homepage recommends typing: ncftpget ftp://ftp.xs4all.nl/pub/crypto/freeswan/freeswan-\*). Some patience!

Note: This setup will NOT be able to handle interacting with IPSec implementations that require X.509 certificates for authentication. For that, you will need to patch your FreeS/WAN sources and figure it out for yourself... or wait until I Wiki it when I need to do it myself :)

Also note: I assume you know how to configure/compile/install kernels.

Step 1: Preparing kernel sources (not necessary if you already have them to hand) cd /usr/src/ tar xjf /download/linux-2.4.20.tar.bz2 <configure your kernel here. this is important.> <compile your kernel here. this is important.>

Step 2: Preparing FreeS/WAN sources cd /usr/src/ tar xzf /download/freeswan-1.99.tar.gz

Step 3: Start making FreeS/WAN cd /usr/src/freeswan-1.99/ make oldgo

Step 4: Rebuild the kernel cd /usr/src/linux/ <At this point you may wish to make menuconfig and change the IPSec to be statically compiled instead of as a module..> <compile your kernel here. again>

Congratulations! You now have an IPSec enabled kernel in the directory where your newly compiled kernel normally lives (/usr/src/linux/arch/i386/boot/bzImage for me). You are probably going to want to copy it somewhere and either restart or rerun lilo and restart, depending on your preferences.