I can't find any authoritative source that can concisely explain the difference between a bridge and a switch. As far as I can tell, most devices commonly referred to as "switches" fit the description of "bridge" as defined by the IEEE 802.1D standard. While it may be the case that a device can be both a bridge and a switch (perhaps "switch" is a subset of "bridge"?), I can only find "hand-wavy" explanations of the difference. The most commonly cited differences I have come across boil down to one of these two:
- Switches have many ports, bridges only have two (or some other small number)
- Switches perform forwarding in hardware, while bridges perform it in software
I'm unsatisfied with these answers because:
- The IEEE standards clearly don't state or assume that bridges will have only two ports. If anything, the assumption is that there will be many more than two ports. So this explanation is simply absurd. (Even Cisco attempts to pass this off as one of the differences).
- The IEEE standards seem to define "bridge" by what it does, not by how it does it. There's nothing in the standard that I could find that says bridging must or should be done in software. So a bridge that forwards in hardware would still be a bridge as far as the standard is concerned.
In fact, when I searched the IEEE 802.1D standard, there was no mention of the word "switch" at all. So "bridge" seems to be the technically correct term. However, since the word "switch" seems to be more commonly used (by far) I can't help but wonder if there is some actual differentiating factor. Or is this just a case of different words being used to describe the same thing?
References to sources would be especially appreciated.
EDIT: I should add that I am fully aware of the fact that bridges are not the same thing as repeaters.