Can you post a capture of your Status/WAN section page when you are using manual DNS and post a picture of the CMD box of the results of the IPCONFIG /ALL listing the 4 DNS addresses? The routers IP configuration is irrelevant here.
Certainly, here's the IPCONFIG output for my ethernet adapter when the router has been configured without DNS relay checked:
http://goo.gl/f2YZUAnd here is a picture of the Status/WAN page:
http://goo.gl/kRmrJAnd here is the same when it has been configured with DNS relay checked:
http://goo.gl/HCuZvand
http://goo.gl/PUdJRYou'll notice that although the IPCONFIG output is different for the two cases (the first showing the 4 DNS servers (the two I configured and two from my ISP) and the second showing only one server, the local address of the router), the WAN status page is identical in both cases (except for the amount of time it had been connected since I released and refreshed the DHCP address from my ISP).
When in the configuration with the 4 DNS servers, I cannot get *any* DNS queries to work. Ping commands from a Windows command prompt fail. Attempts to open any webpage fail.
Interestingly, though, I also tried using the System Check tool on the Router's TOOLS page and typed in www.google.com and it told me that www.google.com was alive, even though when I put www.google.com in as a web browser URL, the browser was unable to resolve it. I suspect Windows is freaked out about having been given the 4 DNS servers, whereas from the router's point of view, everything is OK.
I suspect that the DHCP server in the router is what is broken here.
When DNS relay is not enabled, it seems to be giving Windows all 4 addresses, the statically configured ones AND the dynamic ones from the ISP. If there are static DNS servers configured, it should give out those addresses to clients. If there are no static addresses configured it should give out the addresses from the ISP. It should never give out both sets.
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bc