Linux 






... diagnosis tools : tcpdump, netstat etc.
* The xinetd daemon operation & ports/sockets
* Limiting access to services using
TCP wrappers
Securing
Networks:
Firewalls
* Netfilter overview
* Packet filtering using iptables
* Rule targets
* Network address translation
* Source and
Destination NAT configuration
* RedHat supplied tools for iptables configuration
more...