Hi, I wonder if anyone can help me I have a Class C network (e.g. 192.168.0.1) which is fed from the outside world via a router on which I cannot change the routing as this is out of my control. I have in this network I have a Windows 2008 R2 standard machine with 2 network cards. One of these cards is connected to the router and has a suitable address (192.168.0.10). I would like to add a small subnet on the other card using some of the addresses that are in the local network, for instance 192.168.0.12. I know that I can do this by configuring the second card on the Windows machine to allow IP Forwarding to make it act like a gateway. What I need to do is to turn on proxy arp so that the external router can ask for the address of the machine on the private lan and get back the mac address of the windows server acting as the gateway. My question is, a) does Windows 2008 R2 do proxy arp in this way, 2) if so how do I turn it on.As I said altering the router is not an option so Proxy Arp is the only option that I have. I have had this working with Linux as the gateway but unfortunately the requirement I have is to do this with windows. Thanks Terry

You do not need IP forwarding on if the machines are in the same IP subnet. If both segments are in the same subnet you need bridging, not routing. If they are in different IP subnets you use routing. Windows Server can certainly do proxy ARP. That is the default config for remote access. http://technet.microsoft.com/en-us/library/cc958008.aspx Bill

Bill, Thanks for the answer, but unfortunately this isn't what I need. I really do need IP forwarding as this is all part of a bigger solution. I can do this quite happily with linux, in that I turn on ip_forward and proxy arp on the network cards involved and it all works fine. I am trying to replicate this with Windows. I did look at bridging but the moment I try to set that it comes up and give me a warning about wanting to change my IP address. From my understanding this will set up a NAT which is not what I want at all. I did look at the page on proxy arp but all that tells me is that it is possible, but not how to get it going. I can get packets forwarded from the remote client onto the main lan but when the router arps for the client to send the reply no-one responds and this is the problem. Thanks Terry

No, bridging has nothing to do with NAT. NAT (Network Address Translation) only works on a router. It allows machines on a private LAN to access the public network. The NAT router accesses the public network for its clients using its own public IP. A bridge simply forwards traffic in both directions. Both segments are in the same IP subnet and all machines behave as if they were in the same segment. This appears to be what you want to do. Personally I would use NAT. If you know how to do this in Linux why not use that?Bill

Hi Bill, My fault there, unfortunately someone gave me a wrong steer how to turn on bridging and told me how to turn on Internet Connection Sharing instead. When I found out how to turn on bridging properly then of course it worked. However now the two lan couplers have been replaced by a single bridge and this has lots of implications for the software that will be running on this box. This is also the reason why I can't run Linux. Anyway, thanks for the help, I guess what I'm trying to do can't be done with windows. Cheers Terry

ICS is certainly a bum steer. ICS is just a cutdown version of NAT which came out with Win98. In my opinion it should never be used in a server OS. Bill