I'm in the process of simplifying our home/office network as I'll be relocating temporarily 2500km away. Opted for the TP-Link Omada system as it looked simple, reasonably complete (all components needed) and product was available. 

First impression has not been good. Can't get the OC200 or a software controller to play nicely with the R605 adoption unless I stick with the default IP scheme (which is not good for me). 

Ignoring the OC200 and trying to work with the R605 only, factory default other than the username/password, I'm still struggling with the system. The current issue is DNS and setup is as follows;

- R605 WAN connected to office LAN (R605 WAN IP 172.16.36.151, DNS 172.16.36.41, Gateway 172.16.36.1, all received from the office DHCP)

- The DNS server is DNSMASQ on local server (upstream DNS server is NOT the ISP or 8.8.8.8)

- Gateway Firewall redirects all DNS traffic to internal DNS server (IP Tables rule)

- Linux computer connected to R605 LAN port, DHCP enabled (IP 192.168.0.xxx, gateway 192.168.0.1, DNS 192.168.0.1)

- All settings on the r605 factory default (yes I have tried changing all sorts of settings on WAN and LAN, and defaulted the unit many times)

The issue I am having is that the R605 refuses to use the provided DNS server for requests. fails both on the Linux computer as well as directly on the router (Diagnostics). It will not take internal FQDN or external FQDN. 

From the Linux computer, I can ping, ssh, browse http on the internet, provided I use the IP address. I was SSHed into the DNS server through the R605 while fighting with this. 

Without running WireShark between the DNS and the R605, is there anything known that would cause the R605 to refuse to use a DNS server that is not it's WAN gateway?

My only thoughts is that the R605 is programmed to only use a DNS server preprogrammed into the firmware. 

The current office network has been in place for ~3 years without a hitch. Gateway is an Edgerouter X (DHCP WAN), Switches are mostly TP-Link Jetstream, DNS is hosted on an HP DL server with quad bond gbit nics. All VLANs removed and only configurations on the switches is to support the bond network cards on the servers.