testing UDP ports

[Red Squirrel]

What is the best way to test that a UDP port is responding? From my understanding of UDP, it never really "responds" unless it's built into the layer 7 protocol being used. So if I want to test whether or not a UDP port actually is open or blocked, what is the best way of doing this?

 

[Crusty]

tcpdump

I know the name says tcp... but it can capture UDP packets too. You can probably also use netcat to open up a port to listen on as well.

 

[n0cmonkey]

nmap