What does "Default Server: Unknown" mean for Windows nslookup

Solution 1:

Nslookup will try to resolve the name for the ip address of the DNS server configured as the primary DNS server on the client by performing a reverse lookup of the ip address. If you don't have a rDNS zone set up for your network/subnet you'll get the "server unknown" message as nslookup will be unable to resolve the name for the ip address.

It's not an error condition and won't cause any problems for normal AD and DNS operations.

Solution 2:

Your server isn't returning a reverse lookup for its name. That's why you're seeing "Unknown" there. You'll need to create the appropriate reverse lookup zone to allow your server to reverse-resolve its own IP address back to its name.

Solution 3:

Well, after adding reverse lookup to my internal DNS server, Default Server now show the domain name of my DNS server.

Sample output:

C:\>nslookup
Default Server:  nlserver.dev.nls
Address:  172.27.0.12

NOTE: If there are multiple names mapping to 172.27.0.12 , Default Server will randomly display one of the names.