@bifkit 

Log into the router and go to Advanced > Network > DHCP Server > Modify the Primary and Secondary DNS servers to point to a internal IP.

@Tony 

Please read the entire post before replying. In the first paragraph, I mentioned that I am prevented by the router from changing the DNS to an internal IP, not that I don't know where the setting is.

Thank you.

@Tony

I suppose I should take my own advice and read your reply more thoroughly before snapping back with a quick response. I apologize for my tone, but the problem I am having can't be solved in the DHCP settings either.

My network is dependent on Active Directory and our domain controller, which also must act as our DNS. To simplify matters, the domain controller is also our DHCP server.

The TP-Link router must be able to point to our local DNS, and the DHCP server must be disabled. Therefore, the workaround of assigning the local DNS via the router's DHCP settings won't work.

When trying to point the router to our DNS via the Internet settings, the GUI refuses to save the address, and displays "DNS server IP address and LAN IP address cannot be in the same subnet. Please enter another one." This is incredibly frustrating, and ought to be configurable via firmware.

Thank you for your help.

Daniel

@bifkit 

Would it be possible to set the DC to designate the default gateway to the A20, and the DNS (itself)?

And in turn disable the DHCP on the A20, similar to setting up the A20 in WDS. 

That way the connected devices to the A20 will send the DHCP requests, and in turn the DHCP sever will give the needed info rather then relying on the router to do that.

@Tony 

That is exactly how I'm trying to set it up. The A20 still needs to be assigned DNS information, and as far as I can tell, there is no way to configure the A20 to perform a DHCP request on the LAN. There is only a field to manually specify the LAN IP.

@bifkit 

I will look into this further, and see what I can find for you.

@Tony Thank you for your help.

@Tony Have you had any luck?

@bifkit 

Apologize about the delay.

Here is what I was able to find.

With respect to the restriction of the LAN IP there is no way around that within the router.

As a workaround, using another router is what was suggested.

You would connect the DNS server (DC) to that router, changne the DNS servers IP address to be in the same subnet with the WAN IP of the Archer A20.

Internet > other router > Archer A20 > PC                  

                                |

                (Domain Controller)

@Tony Why wouldn't I just use that router instead of the A20?