Thank you Falko. I already have a domain registered and I use Ispconfig2 as primary server and I have windows secondary dns server.
I want to replace those two servers with a primary and secondary Ispconfig3 servers but I can't do that in one step because I will have problem with my customers(because both dns servers will be offline at the same time and we are ISP).
My question is will the existing records on the primary server be created on the secondary mirror server if the secondary server is added after I create some records on the primary(for example 4 months after the primary server is created)?
Does the secondary mirror server constantly take informations from the primary or only when something is added?