Windows xp validating identity firewalled
If the server uses the NAT address, it fails to connect because no application is listening on that machine.
Some NATs support the configuration of forwarding rules to allow external machines to connect to a particular internal machine.
Network address translations (NATs) and firewalls are common examples of intermediate applications that can participate in network communication.
Windows Communication Foundation (WCF) transports, and message exchange patterns (MEPs) react differently to, the presence of NATs and firewalls.
Packets are filtered, routed, analyzed, and transformed both on the endpoint machines and by intermediate machines on the network.
Intelligent firewalls can also examine the contents of packets to make decisions.
These firewalls come in many different configurations and are often used for specialized applications.
This causes the server to fail when it attempts to open a connection back to the client.
If the server uses the client's perceived address, it fails because the client address cannot be publicly routed.