You obviously don’t know what the Internet is, or how it works.
But this is not only at home or in the office. You can also do this on the network yourself. It is not difficult to rent a VPS in DC which you will use as an alternate DNS server.
Nice DNS split. Yes I can distribute addresses both internally and externally on the Internet. That’s fine, but that’s not what I’m saying at all.
Currently, there have been alternate DNS servers available for years. This is mainly used for things like the “dark web”. Google can’t get there and it can’t index sites either. But search engines can also be found in this part of the Internet.
There are alternative FQDNs that have not even been released by ICANN.
ICANN “runs” the regular Internet. But the Internet is nothing more than a large number of computers connected to a central network. The regular part is easily accessible.
The alternative part is a little trickier, but good research does wonders. You hear a lot about the TOR networks and the legal content out there.
But don’t forget that a lot of things are simply not visible or accessible through regular DNS servers and search engines. Much of the internet is behind alternate DNS servers.
This saying..
You can isolate the Russian population from the regular network. What then? The Russians can then adapt the ISPs to the alternate DNS servers. And even issuing new IP blocks. So this information is still disseminated internally in Russia itself.
The only thing you can really do to withhold information. Do all the lines physically cut. As the Russians did in Ukraine, they are destroying communication stations. But that won’t stop everything either. We still have the Iridium network and the MUSK network. This can still provide people with channels of communication without the need for physical lines.
In any case. The Internet cannot be turned off. Physically impossible. What could be the data is disabled. This is now also being done quite often as can be heard in the news.