nc — checking ports and transferring data

Cheat sheet

• nc -zvw3 host 22 is the port open? (refused vs timed out)
• nc -zvu host 53 UDP
• nc -zv host 20-25 a range
• nc -l 9000 listen (a test server)
• echo data | nc host 9000 send
• nc -l 9000 > out.bin receive a file (on the other side — nc host 9000 < file.bin)

Options

Option	Meaning
-z	scan mode: only check, don't send data
-v	verbose output (refused / open / timed out)
-u	UDP instead of TCP
-l	listen (server mode)
-p N	the local port
-w N	connection timeout, in seconds
-n	skip DNS resolution (faster)
-k	(with -l) don't close after one client