The basics are that I'm trying to RDP into a system that is behind the firewall from outside the network, but the situation is a little more complicated than that and I've run out of ideas for things to try. I'll try and describe the network and firewall setup as clearly as possible:
There is a main location where the RDP server and the firewall are (10.2.0.0/16 network), and a remote location where the RDP client is (10.1.0.0/16 network). The two locations are connected through Cisco site-to-site VPN devices, which also serve as the network gateways. The internal and external interfaces for the sophos have been configured to be on the 10.2.0.0/16 network with the default gateway set to the local Cisco device. The installation wizard added the standard firewall rules to allow DNS, Terminal Applications, Email Messaging, and Web Surfing from the Internal (Network) to Any destination.
Without creating any additional firewall rules, the RDP connection fails, never getting past the "Initiating remote connection" phase and the firewall logs that it dropped the ACK SYN packet from the RDP server to the client. There is no log of a request from the client to the server or anything other than the failed ACK SYN packet.
If I add a firewall rule that allows Any traffic from the Internal (Network) to the 10.1.0.0/16 network destination, the RDP connection still fails, but it advances to the "Configuring remote session" phase before giving the error "This computer can't connect to the remote computer. Try connecting again. If the problem continues, contact the owner of the remote computer or your network administrator." The firewall log shows that it allowed the ACK SYN packet from the server to the client, but there is nothing else in the log to indicate why the connection failed.
The RDP connection worked fine before the firewall was put in place in the network, so I'm pretty sure that it has something to do with the problem, though I don't know if it is because of the network settings, the firewall settings, or what. Any insight would be greatly appreciated.
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