Have two new Vigor 2860 routers (no wifi) upgraded to 3.8.2_VT1

One working perfectly, the other will not pass DNS. Can ping a website by IP but not by name, NSLookups time out, this happens when my client points to the router directly for DNS OR if I specify google dns, cannot resolve from an external DNS server.

Connection page shows ISP DNS servers and gateway exactly as on working router.

I don't believe there are any config difference between the two except the obvious, login credentials and IP's.

I suspect the ISP will suggest the router is at fault, is there anything in the Vigor that could cause this, is it a known issue?

A search found references to DoS Defence issues but nothing is enabled there at the moment...

Any pointers gratefully received....

Jason.