DNS on Windows Server 2003, 3rd Edition

9. Incorrect Subdomain Delegation

Incorrect subdomain delegation is another familiar problem on the Internet. Keeping delegation up-to-date requires human intervention—informing your parent zone’s administrator of changes to your set of authoritative name servers. Consequently, delegation information often becomes inaccurate as administrators make changes without letting their parents know. Far too many administrators believe that setting up delegation is a one-shot deal: they let their parents know which name servers are authoritative once, when they set up their zones, and then they never talk to them again. They don’t even call on Mother’s Day.

An administrator may add a new name server, decommission another, and change the IP address of a third, all without telling the parent zone’s administrator. Gradually, the number of name servers correctly delegated to by the parent zone dwindles. In the best case this leads to long resolution times, as querying name servers struggle to find an authoritative name server for the zone. If the delegation information becomes badly out of date and the last authoritative name server host is brought down for maintenance, the information within the zone becomes inaccessible.

If you suspect bad delegation, whether from your parent to your zone, from your zone to one of your children, or from a remote zone to one of its children, you can check with nslookup:

C:\> nslookup 
Default Server:  terminator.movie.edu 
Address:  192.249.249.3 

> server a.gtld-servers.net. ...