a router

Primary tabs

introduction

A switch can be thought of as the central component of a single network. It interconnects computers and passes frames among them. A router connects two or more networks. It works at layer 3 of the OSI 7 layer model.

what it is

A router is a secialised computer that looks like a switch. It is a box with sockets. Each socket on a router is designed to have a network plugged into it. The router's job is to send packets between these networks. A router stops local traffic from one network being sent to another network.

a router in a home network
computer
computer
computer
computer
switch
router
ISP network
home network

 

An interface is a point where two things connect. There are lots of interfaces in computerland. A socket, a cable plugged into it that leads to another network and the software that talks a protocol like IP is collectively called a network interface. A router usually has one type of interface: a home router usually has two RJ-45 sockets that talk Fast Ethernet. One connects to the ISP and the other one to the home network. A lot of home routers and switches are combined into one box.

A router works at layer 3 of the OSI 7 layer model. . It has to understand a protocol like the public domain IP (Internet Protocol), Microsoft's NetBEUI or Novell's IPX. If the router talks IP then each packet contains IP addresses such as 200.0.0.1. The router gets the network name from each address by using a netmask along the lines of 255.255.255.0.

A central network that connects lots other networks uses plenty of routers. The central network is called a core network. The core network is surrounded by edge networks. The Internet is many thousands of networks connected by routers. Routers send packets across the Internet. The traceroute command lists the routers between a client and a server.

routers in the Internet
router
router
router
router
router
edge network
Internet

The Internet networks are similar to road networks. A few main routes join major destinations. Many minor routes connect minor destinations. An Internet core network is surrounded by edge networks used by big organisations like ISPs. There are two types of big fat Internet routers used here: core routers and edge routers.

The routers used in the backbone are called core routers. These are powerful computers that have huge routing tables and shift millions of packets a second. A core router has lots of the same type of interface, such as Gigabit Ethernet.

The routers used to connect the core network to smaller networks are called edge routers: an edge router is positioned at the edge of the core network and connects it to an edge network, such as connecting the Internet to an ISP (Internet Service Provider). These are powerful computers that can understand the many protocols used in the edge networks, such as VPN, IPSec and voice over IP. An edge router has a mix of interfaces, such as DS1, Ethernet and ATM (Asynchronous Transfer Mode).

A router does its work using a routing configuration table. This table describes which networks can be reached from each socket, which socket to use if there is more than choice for sending a packet, and which packets should be sent first if there a queue builds up. a small home router configuration table has a few lines. A big Internet router table has hundreds of thousands of lines. A router uses a bunch of routing protocols to maintain its routing configuration table.

People drawing a topological diagram of a network use a round symbol to represent a router.

what it isn't

an ethernet switch. A switch is a layer 2 computer.

where it is

The LIC sits between the Internet and the enterprise network. These three networks are joined by two routers.

routers in the LIC
Internet
enterprise network
LIC
router
router

history

In 1972 Bob Kahn came up with the idea of open-architecture networking, including black boxes that connected networks.

In the 1970s many people had a go at connecting computers like PDP-11s.

In the 1980s commercial Internet routers were developed, making companies like Cisco very rich.