Q: I installed Remote Desktop Gateway, but I can't use it to access systems on a different subnet than my Remote Desktop Gateway server. It says the systems aren't found; why?

A: This is most likely a function of IP routing. Consider if you have two network adapters in your Remote Desktop (RD) Gateway server:

  1. A NIC connected to a public-facing IP address that accepts RD Gateway connections
  2. A NIC connected to the internal network to forward requests

The NIC connected to the public network should be configured with a default gateway. The NIC connected to the internal network won't have a default gateway, which means by default it can communicate only with its local subnet (which doesn't require the use of a gateway). This is why the gateway server is unable to forward requests for servers on the internal network that aren't on its local subnet; it doesn't know how to contact them.

The solution is to add persistent routes to the IP routing table specifying the gateway server for those internal subnets. For example, if my internal network gateway were 172.16.8.1 and the internal subnets I wanted to be able to communicate with were 172.16.0.0/16 and 10.7.0.0./16, I would run the following commands:

Route add -p 172.16.0.0 mask 255.255.0.0 172.16.8.1
Route add -p 10.7.0.0 mask 255.255.0.0 172.16.8.1

The RD Gateway should now route the RDP traffic without a problem.