I don’t understand the essence of domain transfer (how to deal with ns)

Question

Domain Name System

There are several domains, they have NS-ki:
ns1.domen.com
ns2.domen.com
on the same server there is a domain: domen.com
its NS-ki too:
ns1.domen.com
ns2.domen.com
and in the parameters of this domain name (domen.com):
ns1 A (Internet v4 address) **.**.**.**
ns2 A (Internet v4 address) **.**.**.**

Now we need to transfer all this stuff to another server.
Action plan:
1. Transferring files and database
2. Changing A-records for ns1 and ns2 in domain.com???

If I change the ip address for ns1 and ns2 (A-record) on the old server, will the site be opened from the new server (whose nameserver ip I specified)? And then, after updating the dns-ok cache for users, delete records and sites from the old server (on the new one, the same pairs ns1=new_ip1, ns2=new_ip2).
Probably due to the lack of a complete understanding of how dns works, I can’t figure out how to transfer it correctly.

How can I transfer correctly?

Answer 1

For the domain to work:
1. The operator's DNS servers must delegate the domain to your DNS servers. By "your" in this case, we mean "to those on which you placed your zone." Such a delegation in the operator zone looks like this:
(in the com zone)
domain2.com. NS ns1.domain1.net.
domain2.com. NS ns2.domain1.net.
If the servers are still located in another zone, this is enough. If NS-servers have names in the same zone, then special A-records like “where can I find this server” appear:
(in the com zone)
domain1.net. NS ns1.domain1.net.
domain1.net. NS ns2.domain1.net.
ns1.domain1.net. A 192.168.0.1
ns2.domain1.net. A 192.168.0.2
So that the operator can do this, you tell him the names, and, if necessary, the addresses of the DNS servers. This is done through the domain control panel at your registrar, who will then figure out what goes where. For the domain in which the DNS servers themselves are located, specify along with IP addresses, for other domains hosted on the same DNS servers - without addresses, it is enough to specify the names.
2. Your DNS servers must be properly configured. This means:
2.a: All servers have the same zone version, ie. the same request to all servers will return exactly the same response.
2.b: They have a service SOA record and NS records that list all these DNS servers.
Those. for the first case, the domain.com zone will contain the following information:
domain2.com. SOA ns1.domain1.net. dnsadmin.domain1.net. 2011100976 86400 7200 3600000 172800
(numbers at the end are the zone version number and timestamps; dnsadmin… is a service email where @ was replaced with .)
domain2.com NS ns1.domain1.net.
domain2.com NS ns2.domain1.net.
Everything else here is domain2.com records. A, domain2.com. MX, www.domain2.com . A and others - what you need, that is, the addresses of your mail and website hosting, jabber server, DKIM signature, and the like.
For the second case, you need to specify the IP addresses of the servers themselves in the A-records in the zone, because they are part of this zone:
domain1.net. SOA ns1.domain1.net. dnsadmin.domain1.net. 2011100976 86400 7200 3600000 172800
domain1.net. NS ns1.domain1.net.
domain1.net. NS ns2.domain1.net.
ns1.domain1.net. A 192.168.0.1
ns2.domain1.net. A 192.168.0.2
again, everything else here is domain1.net records. A, domain1.net. MX, www.domain1.net . A and any others - at your request.

Answer 2

1. At the hosting provider where the domain is registered, make entries for new ns-servers.
Example:
it was: ns1.domen.com and ns2.domen.com
became: ns1.new.domen.com and ns2.new.domen.com
2. Remove the domain name from the panel of the old host. Don't forget to download site files
3. Create your domain in the new hosting panel, in theory all entries will be registered automatically. If not, then prescribe what the new hoster gave.
The transfer can take up to 2 days.
I forgot to ask if the server is from the same host or not?

Answer 3

As far as I understand, domain.com is your domain, it is also transferred. Then:
1) Transfer all files, databases, etc.
2) On the new server, create DNS zones for all your domains. Everywhere specify new IP addresses. (including for ns1.domen.com, ns2.domen.com)
3) Go to the domain registrar (domen.com), and change DNS addresses to:
ns1.domen.com IP1_NEW
ns2.domen.com IP2_NEW
After a complete DNS update, all clients will go to the new server, and you can delete everything from the old server.