Split UDP port in Windows 10

I have a device connected via the network card to an application installed on a PC with Windows 10. The communication between the device and the application is carried out through a UDP port.

If I stop that application, and start NodeRed, I can send commands and see the log with the response (all via UDP, port 1221).

How could I make a split at the UDP port 1221, so that the respective application works and at the same time I see the data in NodeRed? If I leave them both on, I get an error message that the port is busy.

If it's not using broadcast, and not set to try to share the port then is it possible to change the port at one end or other - then use Node-RED to listen on one - send to the other and have a peek on the way through ?

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Unfortunately I cannot change the port.

But even split from UDP to TCP (or anything else) towards NodeRed (if possible) would not be a problem. NodeRed is very flexible, I can do anything there.

tcpdump is a good tool for packet capture and analysis. It has a number of parameters that allows you to filter and handle network packets. Perhaps there is a Windows version ?

No unless your application has been explicitly wirtten to share UDP ports this will not work. The alternative is to have the device Broadcast on the UDP port and then you can bind a 2nd IP address on the Windows PC and have NR listen on one address and the Application on the other - this presumes though that the device has broadcast capabilities.

The last option is if the switch you are connected to has port mirroring capability - you could put a 2nd ethernet card in the PC and mirror the traffic from the device to the two switch ports - NR would listen to one ethernet interface in the PC and the application to the other.