On one of the mailing lists on which I participate, another participant asked about a better way to connect two computers to the Internet. At the time, she would disconnect one compute from the cable modem in order to connect the other computer to the cable modem.
One of the responses she received was that she could get a simple A/B switchbox that could connect to the cable modem and then, by flipping the switch, could swap back and forth between the two computers.
Unfortunately, she ran and ordered it quickly because it was so cheap.
I write "unfortunately" because that will still be a very inconvenient way to switch which computer is connected. Why? It’s a little more complicated than just flipping a switch…
Windows, as of XP, will detect that you’ve connected to another
device at the other end of a network cable.
Modems, though, at least one cable modem that I ran into in the past, required the computer to be rebooted when you connected a different computer to directly to the modem. It also required that the cable modem itself be rebooted.
Otherwise, it continued to listen for the MAC address that it “knew” was at the other end of the cable. The reboot process was necessary to get the modem to recognize that there was a different computer connected.
She really needs a cable/DSL router to handle the connection. The router option would not have required the rebooting. Even more important, it would have simultaneous connections for both computers to access the Internet and even share files and printers between each other.
As I’ve written before, if you have a cable or DSL connection (or even an Ethernet connection in a dorm room), I strongly recommend that you use a cable/DSL router because it acts as additional protection for your system. The router gets the IP address from the Internet Service Provider.
The local computers get IP addresses assigned by the router. The protection is that no computer on the Internet side of the router can initiate a connection to a computer that’s "behind" the router.
By the way, when you read the term "switch" when reading about networking, it does not mean a switchbox. A network switch is a semi-smart device which has one ethernet cable leading to a source (like a cable modem or a router) and multiple simultaneous outputs.
A switch remembers which device is connected to each port and only sends the data for that decide out the right port. On the other hand, a "hub" sends all data out all ports — and waits for a computer to say "ok, that’s me, I got it." A router has a switch built into it as one of its functions.
and
Why does my computer room need two Switches? What is the difference between a big switch and a small switch?