We have about 20 clients mostly running Win7. The server machine runs WinSBS2003. It manages computers, users and the file server...not much else. The Router is an ASUS RT-N66U. This same model router served us for about 2 years then quit about 4 months ago. I installed another one of the same make and model. About 4 weeks ago our ISP informed me that they had new DNS servers. Our router is our local DNS server and holds the DNS IPs. I checked it and found that it already had the new DNS IPs. Well, about a week ago we lost internet and I discovered that the problem seemed to be DNS. Our DNS configuration was setup about 7 years ago before I was much involved in it and knew even less than I know now. The client computers have been pointing to the server machine for DNS, i.e. in TCPIP properties, preferred DNS is the IP of the server machine. I believe the server has been pointing to itself as preferred DNS. I'm told that the server's DNS management utility is the right place to manage DNS, but our router has been doing most of that. The router has DHCP as well. The router is the default gateway. It does actually seem strange to me that the computers' DNS point to the server rather than to the router, seeing it's the router that holds the DNS IPs. But it's worked for 7 years so we don't argue with success... or do we?
Now back to last week's problem. I found that when I entered the DNS server IPs directly as preferred and alternate DNS for each computer that the computers accessed internet websites OK. So that's how I have it now. But then yesterday I got to thinking about it, and for one test computer I entered the the IP of the router (default gateway) in as the preferred DNS. That also works. But I wonder if I'm using a bandaid.
To add to the confusion, the Android phones quit connecting to wifi. For some of them, if we set Static IP on we can then enter the DNS IPs into DNS1 and DNS2. And then it works. But not all of them work even by doing that. The iphones work just fine with no change whatsoever. Anyway we want guests to be able to connect to wifi using only the wifi key.
But more to the point, what changed? The original configuration has worked for 7 years including the last 4 months since replacing the router. What happened differently a week ago? So that's my issue.