It sounds like it might be the DNS servers at your ISP. If you type ipconfig /all in a DOS cmd window, it should show at least one DNS server address. If the DNS IP address is not the router's address (that is, it's not the same address as the default gateway) then you can test whether the DNS servers are being intermittently unavailable. Not all DNS servers are configured to respond to pings, so you should first try pinging them when your Internet access is working. If they respond in your DOS window then you can try pinging them again when you get this failed lookup error. If they don't work at that time it could be a problem at your ISP.
You haven't specified, but I assume here that all DNS lookups give this error, that is, the error happens to different web sites, etc. at different times.
Some additional preparation here. Try pinging the default gateway, which will be your router's local address. That should work both when your Internet is working and when it is not. If it does not then you still have a local problem, in spite of changing out all the local pieces as you have listed. One last piece of the puzzle is your router's default gateway, which is your ISP's equipment, and the first point of contact from your network into the Internet. If you have access to your router's console you can find it in there, usually on the status page. If you don't have access to the router's console then you can deduce the first IP on your ISP's side by using a trace. I recommend a free ping utility for this, TJPing.
TJPing by Jim Dunne
On there you can trace an IP address instead of ping.
While your Internet is working, try a trace to some web site on the Internet, such as
Cisco Systems, Inc. In your trace you will see the first hop is your computer's default gateway. Hop #2 should be the first point of contact at your ISP, in other words your router's default gateway. Keep track of that trace result, including the IP address of the web site you traced to. Then try tracing to that IP address (not the DNS name as that is the symptom that breaks that causes this testing) when you get your DNS error. If you see hop #2, your ISP's number, then you know everything at your end is working fine and it is most likely a problem your ISP is having. If your trace works all the way to the other end without problem, then you know it's a DNS server-only issue, in which case you can report the problem to the ISP who is responsible for them.
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Rod Carty
http://www.en-consult.ca
Digital Yukon Store
>> The longer the title, the less important the job. <<
The preceding humor inserted by QuipSig
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