nmap

Do a ping scan over a network range

nmap -sn 192.168.178.1-254

Scan a network range for port 22 open and names based on mac address

sudo nmap -p 22 --open -sS -sU -n -T4 -v 192.168.1.0/24

Scan a hostfor all open ports

nmap -sS -p- --open -T4 -n --reason 192.168.1.25

-Ss: TCP SYN scan
-p-: all ports
--open: only show open ports in result
-T4: Set Timer Template to almost highest setting (0-5)
-v: Increase verbosity