I have a Windows 2008 r2 host that is sitting on a DMZ with a cisco router(connected to an MPLS network) plugged directly into the same subnet as the 2008 r2 host (192.168.100.x). The inside interface is connected to my internal network on a 172.28.6.x; the DMZ is 192.168.100.x and the oustide interface is connected to to the Internet. The cisco router has an ip of 192.168.100.250; the internal gateway for the DMZ is 192.168.100.252.
Initially I had no routing issues and from the Windows 2008 r2 host I was able to get to my inside network; get out to the internet and traverse the MPLS network over the cisco router. While I was troubleshooting an issue over the MPLS I changed the gateway of the Windows 2008 r2 host to point the gateway to the cisco router 192.168.100.250. Once I changed the default gateway back to the firewall 192.168.100.252 I lost the ability to route from the Windows 2008 r2 hosts to the Internet and Inside network. When I do a traceroute to the Internet it's first hop is the cisco router 192.168.250.0. It seems like the traffic is not being directed to the default gateway and is instead using arp tables to route the traffic to the Cisco router.
I've read some tech articles that relate to Windows issues with HSRP but I can't nail this specific issue down. My next step is to try to disable the Cisco port.