Summary
We have covered three common configuration scenarios for the IPCop firewall and IPSec VPNs. Although we have not covered the entire topic end to end, we have hopefully provided enough for you to understand how VPNs work and get your feet wet configuring (hopefully successfully) your IPCop hosts for certificate and Pre-Shared Key-based VPNs. There are many good books written on IPSec, including several volumes on building VPNs with Linux by the publishers of this book (such as http://www.packtpub.com/openswan/book, written by the developers of Openswan).
IPSec VPNs, although widely supported, are by no means the easiest to configure. SSL-based VPNs, using the same encryption technology as HTTPS, such as OpenVPN, are quickly becoming popular due to the relative ease of configuration, as well as the simpler nature of the protocol; IPSec, even in conjunction with a protocol such as L2TP, is complex and often broken by firewalls and Network Address Translation.
OpenVPN, in addition to being...