Issues connection multiple devices from one network to one destination

Hello all,

I have set up syncthing on my own computers and on the computers of my sister and mother. All of these networks are segregated as we do not need to share files at the moment and I set up a syncthing instance for each of us on my home server, so one for my sister, one for my mom and one for me. My sister and I mainly use this to sync up our two different computers, of which one is in our own home and one is at our parents’ place.

This setup works perfectly fine when everybody tries to connect from different networks, so everyone connects and syncs files with the server on three different connections. The weirdness comes when all of the devices try to connect from the same network, which happens pretty much every weekend when me and my sister are at home. Only one of the syncthing devices connects to the server. The rest of the devices gets a “No UPnP device detected” error, while I’m sure that there is a working UPnP system on both ends of the connection.

Does anybody have a clue what the problem could be? If more information is needed, I will gladly provide more information.

Thanks in advance,


You should try changing the listen port on all the devices to something else then the others. Perhaps your router is not clever enough how to allocate a port mapping for two peers who ask for the same port.

Setting STTRACE=upnp environment variable would allow you to debug UPnP issues.

Audrius, thank you for the response.

I did change the ports on my server (with the three instances), but never thought of doing that on the other computers. I’ll give it a try when I go back to my parents.

I also tried STTRACE=upnp, but it did not produce relevant information as I remember, but not in the position to verify this at the moment.

Google up how to set environment variables for your OS, as there definitely should be more output.

It could be that the computers, when all on the same LAN, happen to have that LAN set as a “Public” network, assuming they’re Windows. This will stop any of the Syncthings being able to talk to each other. Ironically, I think the 0.12 relaying feature might overcome this, but you’re better off modifying the firewall settings or network profiles to permit the computers to talk to each other.

I’ll take another look when I have acces to those computers and report back with the outcome.

The network consists of 2 Windows machines with syncthing and one running Linux and syncthing. Each of these connect to their own node on the server and not to each other. The reason I set syncthing up like this is simply because I have no need for my mother’s photos or my sister’s homework on my computers and I’m looking to sync computers in different locations.

But I’ll take another look on this as well. Thanks for the input.

Ok, a bit later than anticipated, but here is a quick update. The problem seemed to be in the router. After an accidental restart everything started working again…

The problem was that UPnP did not allow any port forwarding via UPnP after the first request, blocking all other systems from connecting. The next time I’ll start with the router, not with the software.


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