Enable Loopback adapter on Windows Server 2008
netsh int ipv4 set int "Loopback Adapter" weakhostreceive=enabled weakhostsend=enabled netsh int ipv4 set int "Local Area Connection" weakhostreceive=enabled weakhostsend=enabled
Those two lines will save you lots of headaches: in Windows 2008 the network behaviour has changed in a subtle and tricky way. Packets coming in from a NIC will not go out from another one, by default.
If, like me, you were using the loopback trick to publish machines on the internet via ARP Proxying your win2k8 machines will NOT reply correctly by default.
Use the settings above and you’re good to go: packets coming in from the loopback (with the internet address) will be sent back through the DMZ nic and will be routed normally.