* Spammy post quoted removed *
A subdomain is the current best practice, but using a "real" domain name for the AD domain does not in fact have to be a PITA. You do NOT need to duplicate all of the DNS records if you do so either. If you already have an external primary DNS server for your domain then all you need to do with your internal DNS server(s) is to make them the authoritative DNS for all clients of the internal LAN, but set them up so they forward all DNS queries for hosts they don't know about to your primary external DNS.
So, for example, lets say you have an internal only Intranet server hosted on your LAN and you want to name it "intranet.somedomain.com", then you would create an A record in your internal DNS and that could be the only record you have in your internal DNS server with all other queries such as "www.somedomain.com" or "server.somedomaim.com" being redirected to the external DNS server just like it was previously. This works 100% if setup correctly and I've done it more than once for clients.
See http://technet.microsoft.com/en-us/l...(v=ws.10).aspx for more info on possible ways to configure this.