Internet connection sharing
When Internet Connection Sharing ( Engl. Internet Connection Sharing , shortly ICS ) refers to a functionality of the operating system Microsoft Windows that allows without major technical effort, with one or more Windows computers set up an Internet connection.
The computer that provides the ICS provides the services Network Address Translation (NAT), DHCP server ( Dynamic Host Configuration Protocol ) and DNS server ( Domain Name Service ) and thus makes it possible for computer ( Clients ) that are connected via LAN and can use its internet connection without the need for additional services or servers.
The function has been available under Windows since Windows 98 SE . However, all clients there must be in the 192.168.0.0/24 subnet . With Windows 2000 / XP / Vista this is the network segment 192.168.0.x / 24, whereby the ICS server receives the 192.168.0.1. This can be changed. If you want to use the Internet connection share of a Windows from the NT series with Windows 98 SE or ME, you have to use a special client, as described in the help. In practice, however, setting up Internet connection sharing under Windows 98SE and ME is often very tedious and prone to errors - ICS is possible without any problems from Windows 2000 Professional. The prerequisite, however, is that no other device provides the DHCP server service in the same network, as this may only ever be available once per network, as access to it cannot be controlled. Modern DSL routers or WLAN routers often also offer a DHCP server service. When using ICS, the router's DHCP must be switched off, otherwise duplicate IP addresses can occur.
With the advent of inexpensive hardware routers (often also available as WLAN versions), which are mostly offered at reduced prices with online contracts, the use of Windows' own "Internet Connection Sharing" has declined. The reasons for this are the simple installation and the largely error-free operation of the router. These two points were often a major problem , especially with the Windows 98 SE and Windows ME operating systems .
Even under Windows XP, setting up Internet connection sharing is still very error-prone, as the service is often not activated or deactivated as desired. When assigning IP addresses, ICS does not check for conflicts with static addresses that are already in use by computers on the network. By default, the computer that has activated ICS receives the IP address 192.168.0.1. However, this can be changed, so problems can be eliminated by manually changing the IP address.
On October 30, 2006, specialists discovered the possibility of carrying out a DoS attack on the service. The weak point is caused by zero pointer referencing in the Windows NAT helper components (ipnathlp.dll). Attackers can use a manipulated DNS query to crash the service. No patch is currently available.