TL;DR: The Google Wifi router won’t forward consistently unless the target uses DHCP
I recently moved to a standalone linux server for my VPN and set it up with a static IP. I was able to setup port forwarding on my Google Wifi, but it was completely hit or miss on if I would get a “Server not responding” error. After a lot of trouble shooting I figured out my VPN server was doing exactly what it should, but my Google Wifi wasn’t.
Turns out that Google Wifi uses DHCP to keep track of the clients it is dealing with. When you setup a port forwarder instead of blindly forwarding traffic it ONLY forwards traffic when it thinks the client is there. In the case of a static IP this means that whenever the Google Wifi doesn’t think the client is there, which happens a lot, it doesn’t send the traffic. As a result the port is completely dead and you won’t be able to use it.
The answer is obvious, but annoying. You have to set the device to DHCP, then go find it in the Google wifi list and assign a DHCP reservation to it. Once you do that you can then go back and delete out your Port forwarding rules and assign new ones. Although this is a total pain and not really the best way to handle this, it is the only way to get Google Wifi to consistently route traffic on specific ports. Hopes this helps!