We run two Lans on our router, a Vlan ( for public WiFi use ) and Management LAN ( for our hardware ) with no Vlan Tag. Each LAN has its own DHCP scope which uses different subnets.
Within the DHCP settings for each LAN we use a different DNS Server. The tagged Vlan uses a DNS address for a web filtering service and the non tagged ( our hardware ) uses google.
Up until recently, when i upgraded from a fairly old firmware version ( i know i should keep up to date more ) everything worked fine. However following the upgrade the required DNS address is being ignored on the tagged Vlan and instead it is using the DNS address of the management LAN instead which is Google. It also doesn't make any different if the management LAN has the DNS IP address directly listed within the DHCP scope of if we point it back to the local DNS server which in turns forward to Google.
Does anyone have any idea's, i believe our build is fairly straight forward and we have some basic firewall rules other than one which is supposed to reirect all vlan DNS traffic to our filtered DNS address ( just in case someone tried to override the DHCP one ) but that isn't even working.