The All-New Switch Book: The Complete Guide to LAN Switching Technology, Second Edition

4.1. A Switch Is a Bridge Is a Switch

LAN bridges have been commercially available since 1984.^[] For most of their early life, bridges were used to segment LANs, extend their distance, and increase the number of devices allowed beyond the limitations of a shared-bandwidth segment.

^[] The DIGITAL LANBridge 100 was the first commercially available Ethernet bridge.

Early LAN bridges rarely had more than two ports. Performance of these bridges was limited by the (now viewed as) primitive hardware and software capabilities available at the time. Many bridges sold in the old days could not support even two ports at wire-speed. Those that did support wire-speed operation commanded a premium price. Increasing the number of ports on these bridges did not make much sense, as the performance was usually limited not by the LAN attachments but by the internal bridging capacity. It simply was impractical to build high port-density bridges until the semiconductor technology advanced to bring the price point down to commercial reality.

During the 1990s, this is exactly what happened. Application-Specific Integrated Circuit (ASIC), processor, and memory technology advanced to the point where it was feasible to build LAN bridges with large numbers of ports capable of forwarding frames at wire-speed on all ports. Bridges built this way were marketed as switches. It is important to note that the distinction between a bridge and a switch is a marketing distinction, not a technical one. The functions ...