Firstly this is not a request for help, just for interest. Contractors have ripped up miles of bt (uk) cables leaving hundreds of us with no phone line possibly for a week or so (hopefully not!). HA is running quite happily on my NUC. However…router does not like not having an internet connection, phones cannot connect to wifi due to “captive portal” trying to provide diagnostic every time anything connects. Companion app cannot connect to HA because certificates not working. Cannot access ‘File Editor’ to fix anything. I have realised Firewall in router was clearly not setup correctly… I think I might have some work to do! I thought this was not meant to happen with a self contained network. Might be worth pulling the phone line plug out of your router just for giggles…Not!
Wasn’t there an option for the companion app to use a local http connection instead of https? then certificates shouldn’t be a problem.
That only works if you have a proxy server handling SSL.
or spoofed your domain name on your router…
so internally you would access it with https://my.domain.name:8123/ 
Or, if supported by router, use hairpin nat
My router does not support hairpin nat. I am sitting tight on that one. I have sky router. Its the stupid captive portal telling me to check my plugs every 5 minutes I could do without.
Thats bt cable wrapped round the end.
If your router doesn’t do hairpin nat then setting up a reverse proxy like the nginx one is a good idea. I usually recommend to people to set up a proxy and move their certificate settings over there instead of listing them in HA, doubly so in this case. Then you can access HA using http in your network and still use SSL with the public url when it eventually connects again.
Also if it’s going to be down for a while might be worth seeing if you can get a 5g home internet option from Verizon or someone for a month.
Like that NAT solution. I am ok on the 5g usually, out and about, but my house does not have a decent 3g/lte mobile signal. That wire was critical! I will sort that out when it all springs back to life. 10 vans parked up there now (Sunday). Interesting lesson though. Thanks for all your comments.
