disconnected: one LAN connection missing

Hi! I got: 3x Linux machines, GBit LAN; 1x Windows, GBit LAN; 1x Android, WiFi; all connected by the same Fritzbox router.

All devices connect via syncthing, except the Windows box and the important Linux server.

Ping is ok, IPs are in host files, the Linux server is even remote controlled via web and ssh by the Windows machine and SMB file sharing works. All machines use the same ports 22000 and 21027. These are open in the firewalls (just the windows internal and one linux client use a firewall).

One Linux machine was especially ‘connecty’, so I made it the introducer. Later I activated this at the Linux server, too.

I tried: “tcp://host:port” and dynamic configurations, quite some restarts, pings, new connections, new shares, local discovery is activated, global discovery on and off, relaying off (was on several times) … waited for hours… but these two machines don´t connect.

When both are configured with each others tcp:// addresses, the windows box tells something like “the connection could not be established because the target computer refuses the connection.” (but in german). The Linux machine comes up with a simple: i/o timeout (20:40:35).

If I put files in the shared folders, it seems to be syncd via the other clients.

What can I do to help them connect or diag what is wrong?


You could maybe check if the ports are actually open using a tool like Nmap. It’s available for both Linux and Windows.

Under Windows, a problem could be if the network is configured as “public” instead of “private”. And you should see a Windows firewall warning when Syncthing tries to listen on its ports for the first time. Did you grant it to use the ports then?

Cheers André

Thank you for that hint!

turns out: just some ports of the server are open…

And even though the windows firewall got rules to allow traffic for syncthing, nmap thinks the host is down. Only when the Win firewall is disabled, some ports like 21, 23, 80, 139, 445 show up. I would have never expected this outcome.

Sadly I have no idea how to get this fixed, but thats no topic for this syncthing forum.

Keep in mind that Nmap by default checks only a standard set of “common” ports. 22000 and 21027 are not among them.

Definitely a case for digging into what firewall rules actually apply to the traffic in question. In Windows, the public / private network classification is a beast, as firewall rules can be made to match only one type of network.

oh! ok! and right there → another very useful hint!

(On Windows I used Zenmap. ‘Intense scan - all TCP ports’ and ‘intense scan plus UDP’. Even these don´t test everything.)

22000 and others, that I had troubles with, are actually closed.

Thank you, André!

Make sure that the network type in Windows is configured as Private.

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