XGS Firewall DNS Request Route over SSL Site2Site VPN

Question

Hello everyone. 
 I have 2 XGS Firewalls connected via SSL Site2Site VPN, which works good. I created a DNS Request Route for contoso.com (changed of course to my setup) to go to DC DNS IP in main office. 
 This worked for quite some time, now it does not. I experienced this behavior before on another setup and I'm unable to find any error. 
 IPs: 
 Site A - Site B 
 192.168.100.0/24 - 192.168.0.0/24 
 192.168.100.1 Sophos Site A - 192.168.0.1 Sophos Site B 
 DNS Request Route on Sophos Site A: contoso.com 192.168.0.10 
 192.168.100.1 as DNS on PC Site A. I can't get a ns lookup for dc.contoso.com. 
 If I put the DC DNS to PC the lookup works of course....... 
 
 Thank you and Best Regards!

emmosophos · Answer

Hello Sebastian, 
 Thank you for contacting the Sophos Community. 
 How is the DNS configured in the PCs? What suffix are you adding? 
 If the computer doesn't have a Suffix added for DNS, the NSlookup will fail because nothing will be attached to the lookup. 
 Regards,