Question about port 21027


So in my “POC” with syncthing, I have noticed that I haven’t opened the port discovery broadcast.

Quote from the syncthing doc for " Port 21027/UDP: for discovery broadcasts on IPv4 and multicasts on IPv6

The system seems functional even with that port close

What is that port exactly used for ?

Here my setup:

  • discovery server – inbound open: 8443 (TCP)
  • syncthing server – inbound open: 22000 (UDP/TCP)
  • syncthing client – inbound open: 22000 (UDP/TCP)
  • Port forwarding on syncthing servers and syncthing client for the port 22000

So basically what’s the use of the port 21027 and where in my setup i should open that ?

Followup question: is there any way to customize that port?

Regards, David

This port is used for discovery in your local network.

So basically useless on remote discovery ?


oh wow, I’m sorry for the dumb question haha

Thanks a lot for following up :slight_smile:

Regards, David

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