"Error renewing UPnP port mapping for external port"

I synced a small folder on my Windows 7 x64 laptops and Android S4 and Note 2, no problem. I’m now doing the first sync of a large folder (10GB, 30k files). Two of my laptops display this error: “Error renewing UPnP port mapping for external port 43918 on device ‘RT-N16’ ( Post dial tcp ConnectEx tcp: No connection could be made because the target machine actively refused it.”

RT-N16 is the router, but I have no clue what might be happening on port 40404. What’s going wrong here?

The router advertises that we should try to talk to it on port 40404 to negotiate about the UPnP port forward. But when we do, it responds by denying the connection. That’s a bug in either our UPnP implementation or theirs.

So it’s just a harmless message with no other symptoms? Any idea what kind of setting to try in the router’s interface that might correct the situation?

If syncing works, it’s harmless. You probably don’t have a working port forward, but depending on what you’re syncing with etc. that might not be necessary. To narrow down the problem, you could enable some debugging; in a console window, something like

set STTRACE=upnp

then post the log file after the error has happened at least once, as an issue on Github.

But if things seem to work, you don’t need to bother. :wink: