I am a full-time Systems and Network Administrator and have been for 20 years. After all this time, I still get excited when I login on a system shell and I still love a good challenge. Most of my career has been spent working for Internet Service Providers but I also work with smaller companies and non-profit organizations. If you don't see it listed below, I've probably still worked on it but these are the things I love and deal with on a daily basis:
● Linux (Ubuntu, Debian, Centos)
● FreeBSD 2.1.8 thru 10-STABLE
● VPN, Firewalls - pfSense
● SSH/SSL
● Bourne Shell, C shell, T shell, Bash and Shell scripting
● Apache - all versions
● Bind 9 / DNS
● DHCP, FreeRadius
● SMTP, POP3, IMAP with Postfix / Sendmail / Courier / Dovecot / Qmail
● tcpdump, Wireshark, snort and other sniffers and IDS/IPS solutions
● Nagios 3 and 4
● PRTG (windows only)
● MRTG / RRDTool
● MySQL
● VoIP with Asterisk / FreePBX
● Citrix XenServer
● Cisco Switch and Routers