Internet Connection Sharing
| A component of Microsoft Windows | |
|---|---|
| Details | |
| Other names | ICS |
| Included with | Windows 98 Second Edition Windows ME Windows 2000 Windows XP Windows Vista Windows 7 Windows 8 Windows 10 |
| Related components | |
| Windows Firewall Windows Security Center | |
Internet Connection Sharing (ICS) is the use of a device with Internet access such as 3G cellular service, broadband via Ethernet, or other Internet gateway as an access point for other devices. It was implemented by Microsoft as a feature of its Windows operating system (as of Windows 98 Second Edition and later) for sharing a single Internet connection on one computer between other computers on the same local area network. It makes use of and network address translation (NAT).
ICS offers configuration for other standard services and some configuration of NAT.
ICS routes TCP/IP packets from a small LAN to the Internet. ICS maps individual IP addresses of local computers to unused port numbers in the TCP/IP stack. Due to the nature of the NAT, IP addresses on the local computer are not visible on the Internet. All packets leaving or entering the LAN are sent from or to the IP address of the external adapter on the ICS host computer.
Typically, ICS is used when there are several network interface cards installed on the host computer. In this case, ICS makes an internet connection available on one network interface to be accessible to another network. A connection to internet is shared by enabling ICS in Network Connections on the network interface with the internet connection. In special cases, only one network interface card is required and other connections may be logical. For example, the host may connect to Internet using a modem/router configured in the bridge mode and share the PPPoE connection with ICS.
Starting with Windows XP, there are some improvements to ICS. Internet Connection Sharing is integrated with UPnP, allowing remote discovery and control of the ICS host. It also has a Quality of Service Packet Scheduler component. When an ICS client is on a relatively fast network and the ICS host is connected to the internet through a slow link, Windows may incorrectly calculate the optimal TCP receive window size based on the speed of the link between the client and the ICS host, potentially affecting traffic from the sender adversely. The ICS QoS component sets the TCP receive window size to the same as it would be if the receiver were directly connected to the slow link.
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