You do realize that L2TP is only slapped on top of IPsec because Windows is brain-dead? And that you can do with just IPsec?

And you do realize that your method of installing *Swan is just as brain-dead as using L2TP? You make a big mess in the system for no good reason, as strongSwan is a Debian stable package, and you don't use KLIPS.

Your install script makes even more stupid things, like replacing current firewall rules with your own without any regard.

The only thing you got right is to use FreeS/WAN descendant, as ipsec-tools is atrocious.