telnet and netcat/nc UDP and TCP port testing

Telnet: Supports only TCP port check

$ telnet



netcat: Supports both UDP and TCP port check

To test TCP connection b/w two servers use below
netcat      Do this on serverA
then enter "hi"
nc -l      Do this on serverB

To test UDP connection b/w two servers use below
netcat -u      Do this on serverA
then enter "hi"
nc -lup      Do this on serverB

netcat to scan open ports in any server

netcat -z -vvv -n

-z scan
-v verbose
-n perform just ip dont try to resolve host