Nmap Command For Network Admins

Nmap (“Network Mapper”) is an open source tool for network exploration and security auditing.
It was designed to rapidly scan large networks, yet it works fine against single hosts.
Nmap uses raw IP packets in novel ways to determine what hosts are available on the network, what services those hosts are offering, what operating systems they are running, what type of packet filters/firewalls are in use, and dozens of other characteristics.