Assuming the issue is what I think it is, which I'm not quite sure of:

You should be able to set the router so it automatically obtains the DNS server address.

Failing that, give your ISP a quick call. I used to work tech support for a large ISP here in Australia, and we often had to give out the DNS server address if clients' modems weren't picking it up automatically. They were very quick calls, we all knew the numbers off the top of our heads, could just recite them when a client rang up and asked.

<<Crossposted with about 4 posts. What I said may no longer be relevant, or I may have misdiagnosed the problem>>

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T W Hopper
Member, Presbyterian Reformed Church
Currently between churches since PRC closed here - attending Crossroads Christian Church.
Canberra, Australia.