I also don't like wasting time on that. In fact now it's more about understanding rather than changing the DNS; because we could always do a LAN with 2 routers...I tried the same thing yesterday also without success.
Partly the whole router freezes or (like your situation) I cant resolve any websites.
I think I will just replace the router. I already spent too much time on this useless box
It's more about what they gave us, and how come we can't change DNS on our LAN section...
That seems fishy to me and more worrying.