A router is a device that forwards data packets between computer
networks, creating an overlay internetwork. A router is connected to two
or more data lines from different networks. When a data packet comes in
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 or routing policy, it directs the packet to the next
network on its journey. Routers perform the "traffic directing"
functions on the Internet. A data packet is typically forwarded from one
router to another through the networks that constitute the internetwork
until it reaches its destination node.
The most familiar type of routers are home and small office routers that
simply pass data, such as web pages, email, IM, and videos between the
home computers and the Internet. An example of a router would be the
owner's cable or DSL modem, which connects to the Internet through an
ISP. More sophisticated routers, such as enterprise routers, 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. Though routers are typically dedicated hardware devices, use
of software-based routers has grown increasingly common.
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