Folks: I'm moving from an old SBS2003 network to Server 2012, and thought I'd take the opportunity to have a spring clean by creating an entirely new AD. My old domain was mycompany.local, however it seems that best practice now seems to be to use a subdomain of a registered domain, so I've gone with core.mycompany.com.
I've created my first DC (with DNS forwarders added pointing to our ISP's DNS servers), and all is well apart from a dns forwarding issue. If I start an nslookup session on the DC, and query for "myhost", the address is resolved correctly. If however I query for an internet host (eg "www.microsoft.com"), then the query is forwarded on to our ISP DNS, but in the form "www.microsoft.com.mycompany.com", so this of course hits our public DNS. I get the same problem if I query for a fully qualified internal host (eg "myhost.core.mycompany.com" hits our ISP DNS as a query for "myhost.core.mycompany.com.mycompany.com").
I'm sure I'm missing something obvious here, but I can't figure what it is!