Recently I ran across an interesting networking issue when using a DSR load balancing setup when converting from Windows Server 2003 to Windows Server 2008. It seems that microsoft has changed the way that the TCP/IP stack functions, so that when we went to configure the loopback adapters and setup IIS to run our websites, the server was unreachable. Worse it had a negative effect on routing to our production servers, since the server in question runs as an auxillary server for the production sites.
Anyhow, we finally found a great article that chronicles the issues, and how to correct them. It all boils down to a couple of commands on the command line to correct it:
netsh interface ipv4 set interface "net" weakhostreceive=enabled
netsh interface ipv4 set interface "loopback" weakhostreceive=enabled
netsh interface ipv4 set interface "loopback" weakhostsend=enabled
