Most subscribers of internetworks do not communicate with routers, they communicate through them. Network administrators, however, they should deal directly with individual routers in order to install and control them.

Routers are purpose-built computers devoted to internetwork processing. They are vital devices that individually serve hundreds or thousands of users—some serve even more. When a router goes down, or even just slows down, users howl and network manager’s jump. As you might imagine after that, network administrators require foolproof techniques to get access to the routers they manage in order to work on them.

Routers do not come with a monitor, keyboard, or mouse, so you should communicate with them in one of three other ways:

▼ From a terminal that is in the similar place as the router and is attached to it through a cable. The terminal is generally a computer running in terminal mode.

■ From a system that is in a different location as the router and is connected to it through a modem that calls a modem connected to the router with a cable.

▲ Through the network on which the router sits.

In large networks, transmission networks are often physically removed from routers and should have access via a network. However, if the router is inaccessible due to network problems, or if there is no modem connected to the router itself, one must go to position and connect directly to the router. The three techniques to get administrative access to routers are depicted in Figure 4.5.

Even when network administrators manage routers in the same building, still prefer to have access to the network. It makes no sense to have a terminal connected to each router, especially when there are dozens of them stacked in a closet or data room computer. It is much more suitable to manage all from a single computer or workstation

There are some techniques to communicate with a router each made probable by a particular communications protocol. Table 4-2 lists each method, the protocol, and how each is used.