The dns address on your router will be the actual external ip address of the dns server. It is generally best to leave it as automatically assigned as if your ISP changes the address of its dns server ten you will lose domain name look ups but if you have reason for settig manually then ok. The dns address setting on your pc is different. This address is assigned by your router and is not the actual external dns address but is usually the internal address of the router iteself (usually 192.168.?.?). Because of this, when your pc makes a dns request it is actuall sent to the router which then forwards the request to the actual dns ip address. The pc is best left to obtain the address automatically but you may set it manually if you wish. In either case it should be set to the internal address of the router and never to the actual external address.
