Love this website and have learned a lot since I started lurking. This problem is confusing the hell out of me. If I want my local DNS server to be the authoritative of example.com how do I setup my name servers to point to my domain, ie ns1.example.com and ns2.example.com since I haven't even setup my domain yet. I purchased it and its asking for which name servers I want to use. It seems like this should be common and not to difficult to figure out but Google and serverfault.com have been unable to clue me so I thought I should speakup and just ask.
You need to set up a glue record, which will have the IPs of ns1.example.com and ns2.example.com needed to resolve example.com.
What I have done in this situation was to log into your registar's control panel and specify the authoritative name server as the public IP of your local DNS server. Your registrar will always be your point of management for the domain name itself, but you can tell it to use whatever for it's name servers. If you do a WHOIS lookup on a domain, you will see the name servers listed. You want one of those to be the public IP of your own DNS server, which can be set through the registrar.
When you do this, make sure you open port 53 on your firewall to allow DNS traffic through.