Ralf Spenneberg has used Linux since 1992 and worked as a system administratorsince 1994. During this time, he worked on numerous Windows, Linux, and UNIXsystems. Starting in 1998, he has been working as a freelancer in theLinux/UNIX field. Most of the time he provided Linux/UNIX training. Hisspecialty is network administration and security (firewalling, VPNs, intrusiondetection, forensics). He has published several German books on VPN, IDS,Firewalls, and Mandatory Access Control. His two current companies, OpenSourceTraining and OpenSource Security, offer training and support in the NetworkSecurity field. OpenSource Training was the first Sourcefire AuthorizedTraining Center worldwide. OpenSource Security is providing pentestingservices for governmental and commercial clients.