Nmap ("Network Mapper") is a free open source utility for network exploration or security auditing. It was designed to rapidly scan large networks, although 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 (application name and version) those hosts are offering, what operating systems (and OS versions) they are running, what type of packet filters/firewalls are in use, and dozens of other characteristics. Nmap runs on most types of computers and both console and graphical versions are available. Nmap is free and open source.

To install nmap on FreeBSD server from ports, do

            # cd /usr/ports/security/nmap
            # make install clean
            # rehash
            

If you want to install from package (binary), run

            # pkg_add -r nmap
            

Now you have nmap installed. To port scan a site or IP with nmap do the following (nmap domain.extn or nmap IP-ADDRESS).

            server1# nmap bizhat.com

            Starting nmap 3.81 ( http://www.insecure.org/nmap/ )
            at 2006-07-26 15:47 GMT
            Interesting ports on 65.98.61.140:
            (The 1654 ports scanned but not shown below are
             in state: filtered)
            PORT     STATE SERVICE
            21/tcp   open  ftp
            25/tcp   open  smtp
            53/tcp   open  domain
            80/tcp   open  http
            110/tcp  open  pop3
            143/tcp  open  imap
            443/tcp  open  https
            3306/tcp open  mysql
            3333/tcp open  dec-notes

            Nmap finished: 1 IP address (1 host up)
            scanned in 19.783 seconds
            server1#