Ethernet Hubs Explained

An Ethernet hub merges several Ethernet connectors onto a single Ethernet segment. This is an Ethernet hub:

Itís a very dumb device that merges one, or two, or three, or four Ethernet connectors onto a single Ethernet segment. Its intelligence comes at a very low level. It understands only Ethernet. It doesnít know what IP is, and it doesnít care. So we can say that it works beneath IPís radar. Think of an Ethernet hub the same way you think of an old extension cord and multiple outlet strip.

You plug it in in one place where youíve got one connector, and it gives you shared access to several new connectors. Typically, these devices will have light-emitting diodes: lights, indicating how they work for diagnostic purposes. In this case, the lights are directly above the connectors, so I like to mount this one with the connectors facing outward so I can see both the wires and the lights.

You use an Ethernet hub wherever you have a low-cost network, and may need to connect two or more computers to a single Ethernet segment. As soon as two or more devices are connected to this hub, they can use Ethernet to connect with each other from then on.

However, don't attribute too much intelligence to this hub. It's a pretty dumb device. It mindlessly adds more Ethernet connectors, without interpreting any of the transmitted information. Itís not smart enough to share an Internet or an IP address. For that, you need a router.

Ethernet hubs come in a variety of sizes and shapes, from many vendors.

Hereís a four-port one where the connectors are on the back, and the LED indicators are on the front panel Ė a very common configuration.

Hereís another four-port hub that has the same arrangement, with the connectors all on the back, and the diagnostic indicators (LEDís) on the front. They all typically have an external power supply.

This little one actually has a fifth connector for a BNC style of Ethernet Ė an old style of Ethernet that is not in common use anymore.

All of these hubs relay, or broadcast, all of the signals from any connector to every connector. Like an old extension chord or outlet strip, any signal thatís present at any connector is present at all of them.

Thereís no standard for these diagnostic lights. Every vendor uses different colors, different blink patterns, and different combinations of multiple lights to indicate different conditions. In general, though, there will be some more-or-less obvious indication when you have a wire thatís properly connected at both ends. Most vendors use a steady ďonĒ light, to indicate that the wire is properly connected at both ends and thatís usually what they call a ďlink light.Ē A lot of vendors use some kind of a blinking or flashing indication to indicate that data is being passed actively on an interface. About the only thing all these indicators have in common is that for any interface, all of the associated lights are completely off that probably means something is fatally wrong or that no wire is properly connected.

Typically, a hub is installed behind a router. Where the router asserts the extra intelligence necessary to imply and manage IP addresses and thereafter, the hub just mindlessly makes that IP information available through its Ethernet interfaces. So if your house or small business already has a properly operating router, you can install a hub to give access to additional Ethernet devices or computers. Or, in a situation like a college dorm room, where the internet service provider has already set up an Ethernet interface with multiple IP addresses and routing, you would simply install a hub to expand the network for additional computers for your roommates inside the dorm.

A hub is also very useful for diagnostic or troubleshooting or monitoring purposes because it essentially creates a passive wire tap. You can connect debug instruments, monitoring equipment, "packet sniffers", or PC equipped tools to analyze the traffic here for troubleshooting and analysis purposes.

Now, on a scale of intelligence for network components, the only thing dumber than a hub is a passive Ethernet wire or cable. And on that same scale of intelligence for network devices the next device more intelligent than a hub is an Ethernet switch.

This is the text from the movie entitled "Ethernet Hubs", published at You can learn more about the video version and purchase an inexpensive personal license to view it by clicking right here. This text also includes a few static images from the movie.