I've had success with this script https://gist.github.com/interfect/5f68381d55658d334e2bc4619d796476
You should be able to connect to the Chromecasts setup hotspot, get the IP of the Chromecast and then run the script.
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I've had success with this script https://gist.github.com/interfect/5f68381d55658d334e2bc4619d796476
You should be able to connect to the Chromecasts setup hotspot, get the IP of the Chromecast and then run the script.
If I recall correctly it sets itself up as a hotspot (no Internet access) and your phone connects to it to set it up. It may use Bluetooth, but that could also be a different version.
AFAIK the Google Home app is required to set it up, but once set up you can remove/uninstall the app.
In terms of being on your network it will broadcast itself as available on your network.
It also does auto-update, so it will expect Internet access. (It also periodically checks for Internet access.)
I can't even get mine to work WITH an account if I put it on the guest network. That sucker wants full access to snoop on everything. I don't think you'll have much luck, but I'll be watching this thread just in case. Good luck.
Re guest network, it broadcasts to the current VLAN and I think you need client isolation disabled (this is frequently the default for guest networks).