Filing this here per recommendations in bug #2995 which was closed as “by design”.
The static IP gui should not enforce a requirement for DNS and gateway which are not technical requirements for a valid IP network. DNS and gateway are only required for using name resolution and traversing out of the local network. Removing the requirement is the the technically correct implementation as demonstrated by Windows, Linux, and MacOS which all work this way.
While a vast majority of HA users will use DNS and gateway, advanced users should have the option to omit these fields for creating an isolated, private IoT network which deliberately excludes a gateway and does not use name resolution. A workaround would be to set these to non-addressable IPs but that could result in timeouts and latency depending on each device’s network stack.
Maybe I should be more specific about my use case, and one which I think is considered good practice for IoT security/privacy.
I’m using dual NIC on my HA instance. This is supported in the IP settings GUI, which is great.
One interface connects to a default network with DNS and gateway while the other is a private IoT network without Internet access. It’s this second interface for which I wish to have no DNS nor gateway set.