We block Internet access for a lot of our smart devices. All of our control is done through the local server; and, short of updating firmware, the devices have no need to be chatting with the Internet. Unfortunately, our DSL modem/router does not have any sort of parental control, blocking, or filtering features. Fortunately, ISC DHCPD allows you to define per-host options. Setting the router to the device’s IP (0.0.0.0 may work as well) allows us to have devices that can communicate with anything on their subnet without allowing access out to other subnets or the Internet.
Every once in a while, my Windows server says it has no Internet connection. It does. It can even use the connection. But the little systray icon has a yellow glif and it says there’s no connection. It’s cosmetic, but annoying. I’ve discovered, however, that there’s a “Network Location Awareness” service that can be restarted to re-evaluate the connectivity status.