Nmap – Network Mapper is a free and an open source application for network discovery, security auditing application. This application is available for windows and linux both platforms in GUI and CLI mode. Nmap can also be used for some useful networking tasks like network inventory, service discovery, host OS verification and sometimes for network based virus identification as well.
Download Nmap from http://nmap.org/
Some basic commands to Nmap are as follows
-sS TCP SYN scan
-sT TCP connect scan
-sU UDP port scans
-v Verbose output
-vv very verbose output
-O Detect operating system
-sV Service version detection
-P0 Dont ping, just scan
-p Choose your ports
-F Fast scan
For example by scanning:
nmap -vv -P0 192.168.0.3
Would scan the IP 192.168.0.3, print very verbose output, and to scan the machine without pinging it.
nmap -O 192.168.0.3
This would do an OS version detection on the target host (TCP/IP fingerprint).
nmap -p 1234 -O -sV 192.168.0.3
This scan would scan port 1234 and see if it was open, as well as an OS version detection.
