The 5-4-3 Rule
The IEEE identifies a maximum number of repeaters, segments, and populated segments that can be used on any given Ethernet network.
These maximums are known collectively as the 5-4-3 Rule because no more than five segments of cable and four repeaters can exist between any two stations on the network, and only three of the five segments may be populated with computers, bridges, or routers. The other two segments can only interconnect repeaters.
It is easy to verify that the network shown in the next slide complies with the 5-4-3 rule.
It is not easy to identify whether or not the network in the slide after next complies with the 5-4-3 rule.