netcat - nc

netcat
ncat
nc

-n : skip DNS lookups
-u : Use of UDP mode (instead of TCP)
-v : Extensive output
-w : timeout (seconds)
-z : Port scanner mode (zero I/O mode); only listening services are scanned (no data is sent)

Scan port 123 for NTP:
nc -z -v -u 0.us.pool.ntp.org 123


scan ports:
nc -w 2 -z 192.168.10.1 1-1024

nc -v -n 8.8.8.8 1-1000