NMAP is an open source network scanning utility. It has tons of options and is a very powerful tool that every administrator needs to know about. Recently, we were checking if UDP port 88 was open on a certain server. NMAP to the resuce :)..
nmap -sU -p 88 DESTINATION_SERVER_IP did the trick. The “-sU” option forces nmap to only scan UDP ports and “-p” forces nmap to only scan the specified port.