Changing Nameservers - No Downtime?

Changing from registrar to my own DNS. How do registrars do it?

[Thanasus]

I have a domain name: abc.com

It is registered at registrar.com and uses their nameservers:
ns1.registrar.com
ns2.registrar.com

I just got my own DNS server up and running. Works, tested on some new domains. I want to switch the nameserver away from my registrar to my nameservers:
ns1.mydns.com
ns2.mydns.com

Now, I know when I have transferred domains from one registrar to another, it has happened seemlessly. The new registrar takes over the DNS duties and yet there is no downtime.

I am trying to do this same thing but it is not working. Here is what I did:
Plan A

1.) Change nameservers at registrar to ns1.mydns.com and ns2.mydns.com

2.) Add a new zone to my DNS server

3.) Add A and MX records to my DNS server

There is downtime. I am guessing this downtime is due to the new DNS records getting propogated. I have a TTL of 2 minutes of my records but since they are new records from a new zone, I am assuming the first time around takes some time to propogate.

So that brings me to theoretical plan B...
Plan B

1.) Add a new zone to my DNS server

2.) Add A and MX record to my DNS server

3.) Wait a few days for propogation

4.) Change nameservers at registrar to ns1.mydns.com and ns2.mydns.com

Now the problem I have with that theory is I can't see the new DNS entries propogating anywhere wihle the nameserver is still ns1.registrar.com and not ns1.mydns.com. Otherwise, some moron could make millions of fake DNS entries on a DNS server with a short TTL and just clog bandwidth with worthless propogation.

So, how do registrars transfer nameservers from ns1.registrarA.com to ns1.registrarB.com (from one registrar to another registrar) with no downtime?

[py9jmas]

DNS 'propogation' to soley down to old records expiring from other server's caches.
There is no pushing of changes out to other servers. (Accept with notify, but that's only between your master and slave servers)

[Thanasus]

So then how do registrars do it. Since the DNS records won't propogate from ns1.mydns.com until ns1.mydns.com is set up as the nameserver, how do I transfer with no downtime?

[Romeo]

Just set up your own DNS with your full zone file (A and MX). Nobody will see it yet.
When you are done, change the nameserver entries in the registrar's database.
This leads to a change of your domain delegation data in the master .COM zone file for your domain accordingly.
And this is, where the change really happens.
Fresh DNS lookups from new users will get the new information from the .COM master servers pointing to your new DNS-server and requesting their information from there.
However, DNS lookups from recurring users will get answered from many local DNS caches for some time until the local cache will expire.
After a day or so (depending on the TTL value set), your registrar should scratch your domains's old zone file from his own DNS, because otherwise expiring cache servers may perhaps reload from the old source instead of asking your new DNS server.

Regards,
R.

[Thanasus]

Romeo,

Thanks but I tried that as well. I put a full zone file on my DNS server, then I updated the nameservers. However, the domain goes through a period where the domain does not resolve.

I would think that since I am not changing IPs, that there would be no downtime. If you get the old DNS info then you resolve, if you get the new DNS you also resolve. However, I am seeing a time period where nothing resolves.