Nmap possui o sinalizador -sU
para escanear as portas UDP.
por exemplo:
# nmap -sU 192.168.0.39
Starting Nmap 5.21 ( http://nmap.org ) at 2014-08-23 19:02 CEST
Nmap scan report for 192.168.0.39
Host is up (0.00017s latency).
Not shown: 999 open|filtered ports
PORT STATE SERVICE
137/udp open netbios-ns
MAC Address: xx:xx:xx:xx:xx:xx (Unknown)
Nmap done: 1 IP address (1 host up) scanned in 19.88 seconds