Windows 8 In Depth

Packet Filtering

If you use a hardware Internet Connection Sharing router (also called a residential gateway) or a full-fledged network router for your Internet service, you can instruct it to block data that carries services you don’t want exposed to the Internet. This is called packet filtering. You can set this up in addition to NAT, to provide an additional layer of protection.

Filtering works like this: each Internet data packet contains identifying numbers that indicate the protocol type (such as TCP or UDP) and the IP address for the source and destination computers. Some protocols also have an additional number called a port, which identifies the program that is to receive the packet. The WWW service, for example, expects TCP protocol ...