From time to time my Macs mysteriously lose all Wifi and Ethernet connectivity: going to any web site results in Unresolved Host or similar symptoms e.g. spinning wheels. In System References, Network, the Ethernet connection shows green. Routers work fine on other devices.
Issue can only be resolved by restarting the Mac where problem occurred.
I believe it is a software problem although one that is not detected by the usual panoply of diagnostic tools e.g. ifconfig, ping, nslookup … It has occurred in almost every OSX version since Sierra to Mojave.
Thanks for any hint.