The Cisco® 100BASE-X Small Form-factor Pluggable (SFP) is a hot-swappable input/output device that plugs into a Fast Ethernet port or slot, linking the port with the network.
Main features include the following:
-Hot-swappable when deployed, the switch or router does not have to reboot.
-Supports the "pay-as-you-populate" model.
-Interchangeable with other 100BASE-X SFPs on the same line card.
-Supports the Cisco quality ID feature that enables the switch or router to identify whether or not the SFP is a Cisco qualified SFP.
-Optically interoperable with respective 100BASE-X Ethernet interfaces on the same link.

Cisco 100BASE-FX SFP
The Cisco 100BASE-FX SFP (part numbers GLC-FE-100FX and GLC-FE-100FX-RGD) operates on ordinary multimode fiber-optic (MMF) link spans up to 2 kilometers long.