UDP DatagramSocket not working on port forwarding

[Charles Simms]

I am trying to use java.net.DatagramSocket to send DatagramPacket across the internet.

I have some hardware on my internal network which I want to send udp packets to from an external network using port forwarding set up on my Linksys WAG320n router. I can connect using telnet to the hardware proving that TCP and port forward works but when I try to send a UDP packets from an external network it fails.

I can however send the same packet internally and port forwarding works fine.

Am I missing something when programming using the DatagramSocket or is the problem on my router (Linksys WAG320n)