Netstat

This has to be the best command ever! I manage webservers at my work and its probably the most useful command to pull information of who and what is happening on the server from a network ports perspective!

------netstat -r shows you your routing table entries
------netstat -i shows you your network interfaces
------netstat -a shows you what network ports are currently in use on your machine

Use netstat -a regularly and get familiar with the ports that are normally in use on your machine