UDPSocket issues on OS 10.11.4 El Capitan

Hello, I have an application that was working great last year and still works great on Windows; but on OS X El Capitan 10.11.4, there appears to be something strange going on…

I already tried downloading the archived version of the Xojo Application from when I created the app, but that didn’t help: worked on Windows, not on OS X.

I have tried to run the UDPExample xojo sample app and communicate between two El Capitan machines. This is also looking a bit strange with many errors in the feedback window.

Is anyone else seeing UDPSocket issues, or having similar problems? All was working great last year on the same hardware (unfortunately I can’t remember which OS version), but now, not so much.

Many thanks,

Di you perhaps changed a network hardware piece like a router/modem ?
It could be that some hardware router/modem is dropping udp packets.

Check and see if your firewall is on… if you’ve got Enable Stealth Mode turned on, UDP packets will be rejected except for signed apps.

@Derk Jochems
The hardware is the same. The setup works completely fine with Windows, and even works running the windows version of the app from my mac on a VMWare virtual windows machine.

@Greg O’Lone
Yes, I should have mentioned in my original post, the firewalls are off.


Solved it: It was a multicast issue on the network interface. I have solved the problem by adding the multicast address to the routing table.

Found this link as a ‘tip of the day’ on this site:
And what a tip it was!