Continuous "TCP/IP failed to establish an outgoing connection" errors in Windows with Syncthing running

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Recently, I have observed a lot of these errors in Windows. I assume that they are somehow related to Syncthing, as they stop popping up when Syncthing is not running, and immediately start showing up as soon as Syncthing has been started. Also, I can see them on a few different Windows machines, so this is not an issue limited to a single device.

This is what the full error message looks like.

Event 4227, Tcpip

TCP/IP failed to establish an outgoing connection because the selected local endpoint was recently used to connect to the same remote endpoint. This error typically occurs when outgoing connections are opened and closed at a high rate, causing all available local ports to be used and forcing TCP/IP to reuse a local port for an outgoing connection. To minimize the risk of data corruption, the TCP/IP standard requires a minimum time period to elapse between successive connections from a given local endpoint to a given remote endpoint.

The only somewhat “official” sources that I have managed to find are

but they do not really give any specific information.

Does anyone have any idea what the culprit may be and possibly how to fix this?

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I would guess this is us using our listening socket to dial out, for NAT penetration purposes. If the connection is unsuccessful it may linger and block the next connection attempt a minute later or so. I don’t think there’s a knob for this behavior.

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Is this error something that could be qualified as a bug/enhancement or should I just ignore it? Can it have any negative consequences when it comes to general network usage and connectivity?

I have had some weird Internet issues on one of my computers lately and was just wondering whether there might be any correlation here. Probably not, as the other machines all seem to work fine, but still.

Do you think that fiddling around with some of the TCP/IP-related settings in the OS can help to get rid of the errors? Right now, Windows is just using the default settings when it comes to networking and such.

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I think the error is harmless and that there’s no real reason to do anything about it.

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Just once as an idea. I interpret this error message as a kind of “flutter”. Is that also a network or internet problem as soon as a connection is established that it is loaded?

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