Block DNS-Resolving to internal DNS from Guest Network

Question

Hello, 
 we got a guestnetwork in separate VLAN in our company using utm as gateway to the internet. 
 Internet access in guestnetwork is realised with transparent proxy. 
 The utm also acts in guestVLAN as dhcp and dns server. 
 Communication between guest and productive network is not allowed and works fine so far. 
 
 My problem is, that dns requests to internal hosts from guestnetwork are beeing resolved through the utm. 
 For example if i ping a hostname in productive network pc001.xyz.lan from a device in guestnetwork, the request is forwarded from utm to our internal dns-server. 
 The communication to this device is blocked, but the dns resolving still works :( 
 
 Configuration: 
 NetworkServices->DNS-> Global: Allowed Networks = GuestNetwork 
 NetworkServices->DNS-> Forwardes = puplic DNS Servers from Telekom Germany (Currently assigned forwardes shows the puplic + internal DNS-Servers) 
 NetworkServices->DNS->RequestRouting = Domain: xyz.lan , Target Servers: our internal DNS Servers 
 
 Is it possible to forward dns requests form guestnetwork only to the puplic dns servers and not to my internal? 
 
 Thanks for any reply and regards 
 Andreas

AndreasHämmerle · Answer

i found a way to solve this problem: 
 I changed the DNS Servers in DHCP-Config. 
 Before the UTM-Adress was deployed as DNS-Server by DHCP for the Clients. 
 Now the puplic DNS servers are deployed by DHCP for the Clients. 
 
 With this setting my guestnetwork cant resolve internal Hosts :)