Multiple choiceQuestion 1 · Recall
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By the end you can describe the role and function of a router, and explain how modems, the PSTN, dedicated lines and the cell phone network carry data to and across the internet.
Inside the village (your LAN) the switch delivers everything. But a packet for a server on the other side of the world needs roads out of the village and signposts at every junction.
The signposts are routers. The roads are phone lines, leased lines and mobile masts.
Router
A device that connects two or more networks (for example a LAN to the internet) and forwards packets between them, using each packet's destination IP address and a routing table to choose the next hop on the route.
Routers can also join networks that use different types of connection, such as an Ethernet LAN and an ISP's broadband line. A home "router" box usually does more besides: it gives devices private IP addresses (DHCP), shares one public address between them (NAT), runs a firewall, and often contains a switch, a WAP and a modem too.
A router and a switch do the same job.
A switch forwards frames within one network using MAC addresses. A router forwards packets between networks using IP addresses.
A router knows the whole route to the destination.
It only knows the best next hop for each destination network. The full route emerges hop by hop.