Published at LXer:

Ever wondered how attackers know what ports are open on a system? Or how to find out what services a computer is running without just asking the site admin? You can do all this and more with a handy little tool called Nmap. What is Nmap? Short for "network mapper," nmap is a veritable toolshed of functionality to perform network scans. It can be used for security scans, simply to identify what services a host is running, to "fingerprint" the operating system and applications on a host, the type of firewall a host is using, or to do a quick inventory of a local network. It is, in short, a very good tool to know.

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