German router and network products company AVM learned the hard way that this is a bad idea. They use fritz.box for their router interface page and it was great until tld .box became publicly available and somebody registered fritz.box.
Having a reserved local/internal only tld is really great to prevent such issues.
I agree that this is a good idea, but I wanted to add that if someone owns a domain already, they can also use that internally without issue.
If you own a domain and use Let’s Encrypt for a star cert, you can have nice, well secured internal applications on your network with trusted certificates.
You don’t even need a star cert… The DNS challenge works for that use case as well.
I agree, if you’re putting your internal domain names into the public DNS you do not need a star cert.
That is great when using only RFC 1918 IPv4 addresses in the network, but as soon as IPv6 is added to the mix all those internal only network resources can becomes easy publicly available and announced. Yes, this can be prevented with firewalling but it should be considered.
