Good Things to Learn:

- Basic *NIX use, maintenance, and administration
- General TCP/IP knowledge
- Packet filtering (firewalling) (pf, ipfw, iptables)
- Routing/NAT
- HTTP server (apache)
- Mail server (smtp, pop3, imap). (postfix, courier, etc)
- Network file systems (NFS, Samba, etc).
- SSH
- NIS/YP / LDAP
- DNS / BIND
- SQL (mysql, postgresql)
- Intrusion detection