Scan the UDP port:

nmap -sU -p 3478 192.168.1.25

http://www.cyberciti.biz/networking/nmap-command-examples-tutorials/

Or this:

$ nc -vnzu <IP> <PORT>
found 0 associations
found 1 connections:
1: flags=82<CONNECTED,PREFERRED>
outif (null)
src <SOURCE IP> port <SOURCE PORT>
dst <DEST IP> port <DEST PORT>
rank info not available