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My set up is this. server behind router, router has a server and switch connected to it with multiple computers. router used to serve DHCP and DNS, a couple of days ago installed AD, DNS and DHCP on the server, and the server gave out IP's.

For various reasons we had to uninstall the domain on our server. I removed AD, DHCP and DNS from the roles and set the router back to serving DHCP and DNS. Now I can't get computers on the network. I reset my router back to factory defaults, and if I plug a computer directly into the router I can get a IP address, but all the computers behind the switch can't get an IP address and can't see the router. All my computers say unidentified network, and if I ping the router it says host is unreachable.

On the other hand, my wireless devices are just fine and connect no problem. But for desktops, ipconfig /release doesn't release anything and /renew can't find a server to renew on. My router log shows several FIN scans but they are from innocuous websites (google, netgear) and it shows a couple of smurf attacks but they are all from my external IP. Any ideas? the server isn't even connected to the route right now, and all the computers are set for dynamic IP addresses.. I don't know what else to try? Any help?

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Have you reset your switch? Power on/off? – Edwin Oct 1 '13 at 3:00
Yes,, I reset to factory defaults, powere cycled – john Oct 1 '13 at 14:59
Is it a smart switch? if so , there may be a VLAN problem or the bridge priority may be incorrectly set. – Edwin Oct 1 '13 at 18:19
up vote 0 down vote accepted

Turns out this wasn't a router problem. It was a switch problem. I guess a tech had come by at some point and flipped a breaker which messed up our switches, used a spare switch and all is well with the world.

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