A common name for Ethernet at a 100Mbps signalling rate. Simply put, 10 times faster than regular ethernet. There are many different types of media through which fast ethernet can traverse, some are 100base-TX, 100base-T4, 100base-FX, 100base-FL, and so on. Fast ethernet is wonderful because it is backwards compatible with regular ethernet, in that a Layer 2 switch can painlessly allow communication between Fast- and regular-Ethernet segments.

Rather than create separate nodes for these, I'll describe them right here.
  • 100base-TX: Fast ethernet over Category 5 UTP cable. This is the most common incarnation of Fast Ethernet.
  • 100base-T4: More of a hack, this lets you push Fast Ethernet through Category 3 UTP cable. Much less common than 100base-TX; mostly used where there is a large installed base of Cat3 and upgrading would be too expensive.
  • 100base-FX, 100base-FL: Fast ethernet over fiber-optic cable. This is commonly used in trunks between buildings. Fiber is safer to use between buildings than copper, since you don't have to worry about surges. It can also travel a greater distance.
Fast ethernet is becoming obsolete almost as fast as it became common. Soon, gigabit ethernet will take the computing world by storm. Mmmm.. 100 megabytes/sec over the network...