The server is running R1Q2, which is a source code modification of the original Quake 2 server concentrating on bugfixes and additive feature enhancements. The original 3.20 release binaries will be able to connect to the server and play, although I recommend checking out the client binaries of R1Q2 too (available for Linux and Windows, and in source form), and especially the R1GL renderer, which adds support for more resolutions, better fullscreen support and some visual enhancements. The client is compatible with original 3.20 servers, too, should you happen to find any.

Cardassia itself is a 64bit Xen virtual machine running CentOS5 (Quake 2 hardly uses any resources at all), and the Quake 2 server is confined using SELinux. The source code for the policy is available on request for those interested.