Length - Cabletron Systems 100BASE-FX Cabling Manual

Full-Duplex Fast Ethernet Network Requirements
If there is any signal path whose total one-way propagation delay exceeds 2.56 s,
the Fast Ethernet network is out of specifications, and error conditions may result.
To eliminate propagation delay problems, incorporate some form of
segmentation, such as bridging or routing, into the network to separate the
problem signal paths from one another.

Length

The 100BASE-FX specification limits a multimode fiber optic cable segment to
412 m or less. Assuming that a fiber optic cable meets all other limitations for
100BASE-FX usage, it is possible to extend a multimode fiber optic link to an
estimated maximum of 2 km. At a length of more than 2 km, the propagation
delay introduced by the multimode fiber optic cable segment may exceed the 2.56
s limit of the Fast Ethernet specification and cause excessive OOW errors.
Cabletron Systems does not recommend the installation or use of any multimode
fiber optic cable segment that exceeds 100BASE-FX limitations of 412 m.
8-6 100BASE-FX (Multimode)