With ping utility you can check your connection to any host in an intranet or an internet.
With traceroute utility you can see all the path your network data makes up to any host in a network.
With finger utility you can get information about users on some server (if it have that service).
With whois you can get all the information about any domain name.
With netstat utility you can get all the information about all your network connections.
With dns lookup utility you can retrieve all the information about domain name services.
With network sniffer you can capture all packets in your network area.
With network scanner you can know all about opened ports on any network host.
With network information utility you can get all information about a network properties of your PC.
All these tools will help you to make your network to be more safety!