-- Linux / Unix (Installation, setup, maintenance, administration)
-- Apache, nginx, lighttpd, tomcat, etc
-- Sendmail, Communigate, Postfix, Domino, Exchange
-- MySql, Postgresql, Sybase
-- Squid, sams
-- Samba
-- NAT, iptables, ipchains, GRE, route etc
-- OpenVPN
-- Script languages (bash, perl, python, ruby)
-- Organization of antivirus and spam protection, including through Spamassasin
-- Organization of data backup systems
-- Windows Servers (server administration and domain Windows 2003/2008)
-- AD
-- DNS
-- DHCP
-- Group Policy Management
-- WSH
-- WSUS
-- VPN
-- WINS
-- MS Exchange 2000/2003
-- ISA server
-- Terminal server
Security
BackTrack, MetaSploit Framework, NMap, Nessus, OpenVAS, Xspider, Aircrack, etc