Firewalls, IDS en VPN's

FreeBSD Handbook - Firewalls
Firewalls are an area of increasing interest for people who are connected to the Internet, and are even finding applications on private networks to provide enhanced security. This section will hopefully explain what firewalls are, how to use them, and how to use the facilities provided in the FreeBSD kernel to implement them.
IP Filter
IP Filter is a TCP/IP packet filter, suitable for use in a firewall environment. To use, it can either be used as a loadable kernel module or incorporated into your UNIX kernel.
KAME Project
KAME Project is a joint effort of seven companies in Japan to provide a free IPv6 and IPsec (for both IPv4 and IPv6) stack for BSD variants to the world.
Linux FreeS/WAN
Linux FreeS/WAN is an implementation of IPSEC & IKE for Linux. IPSEC is Internet Protocol SECurity. It uses strong cryptography to provide both authentication and encryption services. Authentication ensures that packets are from the right sender and have not been altered in transit. Encryption prevents unauthorised reading of packet contents.
Virtual Private Network Consortium
The Virtual Private Network Consortium, better known as VPNC, is the international trade association for manufacturers in the VPN market.
VPN Information on the World Wide Web
Veel informatie over Virtual Private Networks