Net.TCP Port Sharing

Windows Communication Foundation (WCF) provides a new TCP-based network protocol (net.tcp://) for high-performance communication. WCF also introduces a new system component, the Net.TCP Port Sharing Service that enables net.tcp ports to be shared across multiple user processes.

Background and Motivation

When the TCP/IP protocol was first introduced, only a small number of application protocols made use of it. TCP/IP used port numbers to differentiate between applications by assigning a unique 16-bit port number to each application protocol. For example, HTTP traffic today is standardized to use TCP port 80, SMTP uses TCP port 25, and FTP uses TCP ports 20 and 21. Other applications using TCP as a transport can choose another available port number, either by convention or through formal standardization.

Using port numbers to distinguish between applications had security problems. Firewalls are generally configured to block TCP traffic on all ports except for a few well-known entry points, so deploying an application that uses a non-standard port is often complicated or even impossible due to the presence of corporate and personal firewalls. Applications that can communicate over standard, well-known ports that are already permitted, reduce the external attack surface. Many network applications make use of the HTTP protocol because most firewalls are configured by default to allow traffic on TCP port 80.

The HTTP.SYS model in which traffic for many different HTTP applications is multiplexed onto a single TCP port has become standard on the Windows platform. This provides a common point of control for firewall administrators while allowing application developers to minimize the deployment cost of building new applications that can make use of the network.

The ability to share ports across multiple HTTP applications has long been a feature of Internet Information Services (IIS). However, it was only with the introduction of HTTP.SYS (the kernel-mode HTTP protocol listener) with IIS 6.0 that this infrastructure was fully generalized. In effect, HTTP.SYS allows arbitrary user processes to share the TCP ports dedicated to HTTP traffic. This capability allows many HTTP applications to coexist on the same physical machine in separate, isolated processes while sharing the network infrastructure required to send and receive traffic over TCP port 80. The Net.TCP Port Sharing Service enables the same type of port sharing for net.tcp applications.

Read more: MSDN

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