A repeater (sometimes called an extender) is a gizmo that gives your network signals a boost so that the signals can travel farther. It’s kind of like a Gatorade station in a marathon.
You need a repeater when the total length of a single span of network cable exceeds 100 meters (328 feet). The 100-meter length limit applies to the cable that connects a computer to the switch or the cable that connects switches to each other when switches are daisy chained together.
In other words, you can connect each computer to the switch with no more than 100 meters of cable, and you can connect switches to each other with no more than 100 meters of cable.
The illustration below shows how you can use a repeater to connect two groups of computers that are too far apart to be strung on a single segment. When you use a repeater like this, the repeater divides the cable into two segments. The cable length limit still applies to the cable on each side of the repeater.
Here are some points to ponder when you lie awake tonight wondering about repeaters:
Repeaters are not typically used with twisted-pair networks.
Well, technically, that’s not true because the switches themselves function as repeaters. You typically see repeaters as stand-alone devices only when a single cable segment would be more than 100 meters.
A basic rule of Ethernet life is that a signal can’t pass through more than three repeaters on its way from one node to another. That doesn’t mean you can’t have more than three repeaters or switches, but if you do, you have to carefully plan the network cabling so that the three-repeater rule isn’t violated.
Repeaters are legitimate components of a by-the-book Ethernet network. They don’t extend the maximum length of a single segment; they just enable you to tie two segments together. Beware of the little black boxes that claim to extend the segment limit beyond the standard 100-meter limit for 10/100BaseT cable. These products usually work, but playing by the rules is better.