Port 4321
In live entertainment systems, port 4321 is used by Dante.
udp/4321
Dante — Dante multicast audio (ATP)
Audinate's proprietary audio-over-IP system carrying uncompressed multichannel audio, clocking and device control over ordinary gigabit ethernet. It is the default audio network on most touring and install jobs, and usually what a desk, a stagebox and an amp rack are talking to each other with.
Check it from the command line
npx showstack port 4321
Not what you were looking for?
If you know something else uses port 4321, tell us. Adding it is one file.