Looking at port forwarding in the documentation I see
If this is not possible or desirable you should set up a port forward for port 22000/TCP, or the port set in the Sync Protocol Listen Address setting. The external forwarded port and the internal destination port has to be the same (i.e. 22000/TCP).
Communication in Syncthing works both ways. Therefore if you set up port forwards for one device, other devices will be able to connect to it even when they are behind a NAT network or firewall.
having a couple of minor quibbles about the 2nd sentence in the 1st paragraph, I see I don’t understand it fully.
Presumably this doesn’t apply if you use port address translation (PAT)?
Then there’s the 2nd paragraph.
I have dynamic dns to my house (local.example.com) and at my son’s house (remote.example.com) with port 22000 forwarded to a pi at each end.
Upload at my end is low-speed, and so the remote pi connects only to the local pi. So far, so good, and it all works well.
However, thinking that I might try connecting my laptop to the remote pi to see if that worked better, I can’t see a way to connect without forwarding another port to my laptop. I can see why I don’t need another port forward at the local end.
I am taking the phrase “other devices will be able to connect to it” to imply that they will be able to establish two-way communication. I can’t see how this would work, so I suspect the implication is wrong.
Can anyone clarify?