PPTP (Point to Point Tunneling Protocol)

PPTP is a proprietary protocol created by Microsoft for VPN solutions. To date it has been shown to contain numerous serious flaws. However if you need to integrate Linux into a PPTP environment all is not lost, contains a Linux implementation of PPTP. Fortunately Microsoft is moving away from PPTP towards IPSec.

CIPE (Crypto IP Encapsulation)

CIPE is a free IP level encryption scheme, meant for use between routers. It is appropriate for 'bridging' networks securely together over insecure networks (like the Internet). The official cite for CIPE is at: http://sites.inka.de/~W1011/devel/cipe.html. We would however recommend FreeS/WAN as a better long term solution. CIPE is very easy to setup for two servers but anything more than two servers becomes a configuration nightmare.

IP Security (IPSec)

IP Security (IPSec) is the encryption of network traffic. You cannot encrypt the header information or trailer (i.e. the IP address/port the packet is from, and going to, the CRC checksums, and so on), but you can encrypt the data payload. This allows you to secure protocols such as POP/WWW without having to change them in any ways, since the encryption occurs at the IP level. It also allows you to securely connect LANs and clients to each other over insecure networks (like the Internet). Currently IPSec for Linux is in testing, however there have been several stable releases, and We ourselves have deployed Linux based IPSec servers successfully.