Nslookup server: unknown between VLANs/networks?

I have several VLANs/networks - eg.:

• 10.0.10.0/24 : Servers
• 10.0.20.0/24 : Pcs

My DNS server is called "DC1.mydomain.local" (IP 10.0.10.11) and I have a PBX server called SVPBX (IP 10.0.10.21).

Inside the Servers VLAN - If I type Nslookup SVPBX, I get this result:

C:\Users\x>nslookup SVPBX
Server:  DC1.mydomain.local
Address:  10.0.10.11

Name:    SVPBX.mydomain.local
Address:  10.0.10.21

But if I inside the PCs VLAN tries the same, I get this:

C:\Windows\system32>nslookup SVPBX
Server:  UnKnown
Address:  10.0.10.11

My PCs DNS is set to: 10.0.10.11.

I have created two reverse lookup zones on the DNS server (DC1):

• 10.0.10.in-addr.arpa
• 20.0.10.in-addr.arpa

Any idea what I am doing wrong? Shouldn't I create a reverse lookup per VLAN?

This is not about reverse DNS. Reverse DNS zones contains PTR records, whilst you're looking for A/AAAA records with your nslookup commmand.

Your problem is the DNS search domain. On the first PC, where it works, the search domain is probably set to mydomain.local. This can be verified with Get-DnsClientGlobalSetting cmdlet in Powershell.

You should not rely on the DNS search domain in your configuration files. Always use FQDN. The search domain can commonly be specified by DHCP server, and may open you up to attack by software connecting to a different server than anticipated.