What is an Ethernet Bridge?

Robert Grimmick

An Ethernet bridge is a type of computer networking device that connects two or more distinct segments of a network. It overcomes some inherent limitations of the widely used Ethernet networking technology by actively managing the flow of data between network segments, forwarding only those pieces of data that originate on one segment and are destined for another. An Ethernet bridge reduces overall network congestion and allows larger and more complex networks to be built. Additional network interfaces can link Ethernet segments over technologies like Wi-Fi® and power-line networking.

An Ethernet cable.
An Ethernet cable.

Ethernet is the most popular standard for wired networking, found in both home and corporate Local Area Networks (LANs). Ethernet-based networks can be extremely complex, linking the computers, printers, and other resources of an entire company. The number of devices on a network and the geographical area that network can encompass, however, are limited by some inherent characteristics of the technology. Only a single device or “node” on the network can transmit at once, and a greater number of nodes on a network means a greater chance of a disruptive collision in which two or mode nodes send data at once. The electrical signals used by the technology can also degrade as wire length increases, limiting the practical maximum distance of an Ethernet cable.

Ethernet cables plugged into an Internet switch.
Ethernet cables plugged into an Internet switch.

To combat the limitations of Ethernet technology, several types of networking devices can be used. An early device known as a repeater could extend the range of an Ethernet cable by retransmitting electrical signals, but had no protection against collisions. In more modern networks, an Ethernet switch, bridge, or router may be used to segregate network traffic and prevent collisions. Bridges historically had only two Ethernet ports, one for each network segment, but many manufacturers have used the terms switch and bridge interchangeably, and a bridge today may have many ports. Routers are more complex devices with advanced features.

An Ethernet bridge serves as both a demarcation point between network segments and a link between those segments. The bridge actively manages data flow between two or more segments, forwarding only data originating on one segment and destined for another; communication between two nodes on the same segment will not be forwarded by the bridge. This reduces overall network congestion and enables larger LANs to be built. The bridge also retransmits signals to keep them from degrading over longer distances.

Though an Ethernet bridge by definition must include at least one Ethernet port, it may include other types of network interfaces to facilitate Ethernet bridging. At the consumer level, an Ethernet bridge might be used to connect a small network segment of home theater equipment and video game consoles to the rest of the network through Wi-Fi® or by using the existing power outlets and electrical wiring of a house or apartment. More powerful devices can wirelessly link an entire office with a second building several miles or kilometers away. Software programs also allow ordinary computers to be turned into an Ethernet bridge, provided the machine has more than one Ethernet port.

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