Port 123
In live entertainment systems, port 123 is used by NTP.
udp/123
NTP — NTP client and server
The protocol that keeps ordinary computers agreeing about the time of day. It corrects for network delay by measuring the round trip and disciplines the local clock gradually rather than jumping it. Milliseconds on a good LAN — nowhere near PTP, and exactly right for its actual job: making logs, licences and scheduled events line up across a rack.
Check it from the command line
npx showstack port 123
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If you know something else uses port 123, tell us. Adding it is one file.