Setting up a Remote Assistance session is relatively easy when both parties have a public IP address given by an Internet Service provider. In this scenario, the computers connect directly to one another, sending and receiving data on TCP port 3389. Furthermore, the Windows Firewall in Service Pack 2 automatically opens up this port whenever a Remote Assistance connection is requested.
However, this configuration is not applicable to many home or small office settings, where networked computers are "hidden" behind SOHO routers. In other words, it's not quite as easy as it sounds for many users because computers behind these routers use private IP addresses.
To check whether you're using a private address, type IPCONFIG at the Command Prompt. If you see an IP address that starts with 192.168…, you have a private address. The public IP address from your ISP has been assigned to the router, and when you send a request for a Web page to the Internet, the Web server sends the page to the public IP address. The router is then responsible for passing on that Web page to the requesting computer.
With such a configuration, the Remote Assistance traffic does not know where to go. But all is not lost. You can still get Remote Assistance to work if you perform the following: