I'm having this peculiar issue with Microsoft DNS.
Basically, we have domain.com that's a split horizon setup (external public DNS and internal DNS are both authoritative for separate zones), don't ask me why, it was like this when I got here.
In this AD we have 3 domain controllers, serving as DNS servers for the internal zones. On top of this, we have 2 DNS servers that forwards queries to these AD servers, and cache the results.
Additionally, we have another domain, example.com that's only in our external public DNS servers.
Now to the problem; AD servers have taken an issue with the name subdomain.example.com. The return queries with "domain name can't be found", as an authoritative server does when it doesn't have a record. However, the DNS forwarders for clients do resolve the query.
Externally everything works fine, subdomain.example.com resolves as it should to a CNAME for www3.domain.com
However, the problem is not with the whole zone, it's only with that specific subdomain. www.example.com resolves both internally and externally as a CNAME for www3.domain.com.
So, how can a DNS server that's not authoritative for a zone reply that a record can't be found?
As a workaround, I created a new zone for subdomain.example.com and added an A record that's identical with the one for www3.domain.com. And an hour later this record was gone?
I'm close to giving up and becoming a goat farmer. :)