UDP

Checking a port is in use

eg udp/5060

lsof -i :5060

asterisk 7032 asterisk 9u IPv4 85198 UDP *:sip

Testing UDP port connections using netcat

nc -vzu 67.216.35.162 5060

And do a tcpdump on the target

tcpdump -A -s 65000 -i eth0 udp