Article ID: 309524 - View products that this article applies to.
This article was previously published under Q309524
Windows XP includes support for Internet Connection Sharing (ICS), which provides the ability to share an internet connection with other computers on a local network. ICS in Windows XP allows services to be mapped to hosts on the internal network, so that requests coming from the internet and destined for a particular service will be redirected by Windows XP to the appropriate computer on the internal network.
For example, you may want to place a Point-to-Point Tunneling Protocol (PPTP) server on the internal network and configure Windows XP ICS to forward the Virtual Private Networking (VPN) traffic to the PPTP server. This article describes the process that is required to map PPTP back to an internal host, so that an incoming VPN connection can pass through the Windows XP ICS computer. For the purposes of this article, it is assumed that the PPTP server is already configured properly and is able to accept PPTP connections from clients on the local network.
A PPTP connection is composed of two types of traffic. The first is PPTP traffic, which uses TCP port 1723, and is used to establish and maintain the connection. The second is Generic Route Encapsulation (GRE) (Protocol 47), and is used to encapsulate the actual data that is passed between the two endpoints. When you configure service redirection in ICS (for Windows XP), it is only necessary to map TCP port 1723 to the appropriate internal server. GRE traffic will automatically be redirected to the same host as the PPTP traffic.
To add the service mapping that will allow PPTP traffic to be passed to an internal host: