A commercial router device

Here is a commercial router. There are many of these available today as commodity items in computer stores. This is a late-90s router by Flowpoint.

Routers are computers, not modems

These things look like modems in scale and construction. Their functions also seem similar. However, routers are far more different from modems than similar. They are similar to-- in fact the are-- computers. Special-purpose, limited to that purpose, lacking keyboards and monitors that some computers have. But they have the defining characteristics of a computer: a processor chip, memory, an operating system, other software. Modems have none of that. The operating system is often an adapted version of linux or BSD unix, since those are are freely available in terms of both source code and cost, so manufacturers like them. Instead of a formally designed router product, home enthusiasts and corporate technical staff sometimes use a PC equipped with linux and configured to the routing purpose. Either does the same job. A router is a computer.

Routers have multiple interfaces

In addition to CPU, OS, memory, commercial routers also contain interface circuitry-- the same as do PCs, where it takes the form of a NIC. The commercial router usually also has a built-in hub, to which its network interface circuitry is internally "plugged in." Several out-facing hub-style ports (RJ45) are available for users to then plug in a few of their own devices. The router below has a built-in 4-port hub. Counting the internal connection, by the router itself, there are 5 ports to this hub. This is only one side of the interface picture (the inside). In order to route a router must have at least 2 interfaces. That's because routing means transferring data between networks, thus handing off data between interfaces. The other interface (the outside) may or may not be ethernet. It could be, for example, frame-relay or some other data-link level interface, if that is the type of other network the router attaches to and the user's data needs to cross. Here is the back view of the Flowpoint router showing its interfaces.

Routers offer management software

For management, this router runs a telnet server when you turn it on and it boots. You can then connect a monitor-equipped computer to it using telnet, and give commands to administer and configure it. Modern residential router products also offer a management interface, but usually via http protocol instead of telnet protocol so users interface with the device using an ordinary http browser. Such devices have a built-in web site (html files) in storage, to project the available management options to the user.

Here is the Flowpoint router's product manual, explaining its capabilities and documenting the commands to control it.