5-4-3 rule

Definition of 5-4-3 rule in The Network Encyclopedia.

What is 5-4-3 rule?

A specification describing limitations for constructing certain kinds of Ethernet networks. The 5-4-3 rule applies specifically to Ethernet networks based on either the thinnet or thicknet cabling option.

Graphic 0-2. Five segments, four repeaters, and three populated segments.

How 5-4-3 Rule Works

According to the Ethernet specifications, thinnet (or thicknet) Ethernet network segments can be joined using repeaters to form larger networks, but there are limitations on how you can do this.

The maximum number of segments you can join is five. To join these segments, you need to use four repeaters because Ethernet typically uses a bus topology in which all segments are joined linearly.

However, in this configuration, no more than three of the segments can actually have computers attached to them, leaving two segments that are used only for extending distances rather than hosting computers.

These two unpopulated segments are called inter-repeater links. You should not violate this rule when implementing Ethernet networks; otherwise, unreliable network communications might result.