Understanding Linux Network Internals

Bridging Different LAN Technologies

In the previous examples, we always saw a bridge with both ports connected to Ethernet LANs. This bridge type is the most commonly used, mainly because the de facto standard for LANs nowadays is Ethernet. However, especially in the past, there used to be bridges with different LAN ports; for example, an Ethernet port and a Token Ring port. Such bridges have one more issue to take into consideration: the differences between the bridged LAN technologies. For example, Ethernet and Token Ring LANs operate at different speeds, and use different L2 protocols and headers. The different speeds require some kind of buffering to be implemented, and the different protocols require the bridge to convert headers from one format to the other, including taking care of those L2 options that are provided by one protocol but not by the other. Linux bridges only between Ethernet ports, so we will not consider the more complex case any further.