A router is a device that forwards data packets across computer networks. Routers perform the data "traffic directing" functions on the Internet. A router is a microprocessor-controlled device that is connected to two or more data lines from different networks. When a data packet comes in on one of the lines, the router reads the address information in the packet to determine its ultimate destination. Then, using information in its routing table, it directs the packet to the next network on its journey. A data packet is typically passed from router to router through the networks of the Internet until it gets to its destination computer. Routers also perform other tasks such as translating the data transmission protocol of the packet to the appropriate protocol of the next network, and preventing unauthorized access to a network by the use of a firewall.
The most familiar type of routers are home and small office routers that simply pass data, such as web pages and email, between the home computers and the owner's cable or DSL modem, which connects to the Internet (ISP). However more sophisticated routers range from enterprise routers, which connect large business or ISP networks up to the powerful core routers that forward data at high speed along the optical fiber lines of the Internet backbone.