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have a problem that I can't seem to find the reason for.

We are running a small network with windows clients(XP/Win7) and windows servers(2008 sp2/2008r2). The domaincontroller is working as DC, DNS, DHCP, VPN. We have a Level1 FBR4000 between internet and our internal network.

The problem is that from time to time specific IP-adresses stops working, the only way I have gotten the devices to work again is to exclude the specific IP from the DHCP address pool and getting a new IP, then everything works again. It seems as the specific IP is beeing banned/blocked somewhere but I just can't figure out where.

Anyone got an idea as to where I should start to look?

I could also point out that I just reinstalled all servers due to a officemove and was hoping to get away from this problem but it just showed up again. This last time it was my iPhone that got stuck through the Wi-Fi...

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Do you have any static IP's assigned to any machines? I've had the same problem once and what happened was that I had a few machines with static IP addresses that were actually allocated inside of the DHCP. So when another computer joined the network, the DHCP assigned the already used static IP to the new machine and it caused both machines to lose connection.

Also, if you have a VPN, make sure that the address range allocated for VPN clients isn't mixed with the DHCP pool that you specified.


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