How to determine if a UDP port is openblocked?

[jadams]

With UDP being connectionless and not giving any kind of acknowlegement its there how can I test if a port is open or blocked?

 

[Mackintire]

Using ipref in UDP mode will give you that info.

 

[Cyberrad]

Using Nmap with the switch -sU should do the trick.

sU tells Nmap to send an empty UDP packet to Nmap’s default port list or port to the ports you specify. If an ICMP type 3 code 3 message is returned then the port is marked as closed. If an ICMP type 3 codes 1, 2, 9, 10, or 13 is returned then the port is labeled as filtered. If a service responds then the port is open. If a service responds and then does not respond to a second UDP packet then the port labeled as open filtered.

nmap -sU -p <port> <target IP>