Ok this maybe a dumb question. But I don't have any clue so I will ask.
I am going to upgrade my servers and move all the accounts. Of course DNS IP's will change.
Last time I did this, I just created exactly same DNS on new server (eg. ns11.server.com and ns12.server.com) and updated the IP address of the DNS on the registrar. However it took more than 2 days for some domains to update the new DNS IP address. It was a nightmare.
So my options are:
1) Do the samething as before
2) Create new DNS addresses (eg. ns5.server.com and ns6.server.com) and update the DNS info of all the domains.
It depends. Registrars are faster these days to propagate DNS changes, BUT setting low TTL values and changing the zone records on your old DNS servers AND changing the IPs for the DNS servers at your registrar is the best combination to ensure quickest propagation.