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I have a server running W2K3. The computer acts as a DHCP, DNS and Firewall for a small network of about 10 computers (inside a larger network, that is no way connected other than by a fiber modem). This server will lose all connectivity to the internet after a few hours, but if the Static IP is changed, then changed back it works fine for another few hours. This happens once a day or sometimes several times a day. I'm not sure what could be causing this, but I can tell you it's causing me some real issues because I can't figure this out.

None of what was suggested resolved the issue. I have tried what was suggested and although I appreciate it, it was not successful in resolving my issue. I have added my ISP's DNS addresses back to the DNS on the Active Directory server. I would prefer to not have DNS on that server and use the ISP's because it is more reliable than ones i've used before. Any recommendations?

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so you're saying your basically using your server for internet connection sharing? Meaning, traffic from the internet goes >>>internet>>>modem>>>server>>>network? Do a tracerout when it works and one when it doesn't and show the results – Eric C. Singer Jan 20 '12 at 3:38
Also, and ipconfig /all would be a huge help. Also, when you say the internet stops working, how can you tell? have your tried pinging by name and IP? If the IP works, but name doesn't, it's a DNS issue – Eric C. Singer Jan 20 '12 at 3:40
It definitely sounds like a DNS or ARP issue. More detail would help. – Tim Brigham Jan 20 '12 at 4:26
I would be glad to post more information: @EricC.Singer: The rought network map you drew is correct. When I do a traceroute I get nothing. It stops at the dns server outside my network. However, last night after posting this. I disabled recursive queries, and defaulted the ISP's DNS as the network DNS and it seems to have resolved the issue (temporarily). I have cleared the arp cache, is there a progream that I can setup to clear DNS and ARP cache automatically? – brad Jan 20 '12 at 13:53

if you have your own DNS server, there's really no need for the ISP's DNS server. Your windows server with default DNS setting should work fine. What I would do, is make sure your root hints are setup correctly, so your dns server knows how to resolove queries. Don't point unresloved queries to your ISP as you'll then have a dependency on them for DNS, and IMO, that's the beauty of having your own DSN server. See below to update your root hints..

Then remove the IP in your DNS forwarders...

Clear the cache in your DNS server

Flush your local resolver cache by running IPconfig /flushdns from the commandline and then try a new DNS query. if it works, you're now utilizing your own DNS server. At this point, it should be rock stable.

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