Networking Connection Rules
The University of Findlay's College of Education

In the days when the bus topology dominated most network devices, a simple rule was established to minimize network errors. The 5-4-3 rule states that ethernet can have no more than five segments, with four repeaters and only three of those segments can have computers connected to them.

This rule applies to networks that contain repeaters. A repeater is a device that enables the network signal to go a farther distance. Technically a hub is a repeater, but the 5-4-3 rules doesn't apply to an environment with hubs. I am only explaining the 5-4-3 rule because most networking people still apply this rule to an environment with hubs.

In the hub environment, you may have no more than three hubs on a segment.

A more modern version of the 5-4-3 rule is the 2-1 rule. This says that no more than two segments and each segment must connect to a switch. This is the model you should use in your school.