Classic Ethernet (IEEE 802.3) design rule: what is the maximum number of cable segments that may separate any two nodes on a shared coax/repeater-based network?

Introduction:
Legacy shared-media Ethernet (before modern switches) followed physical-layer rules to ensure collision detection and timing integrity. A well-known guideline is the “5-4-3” rule, which constrains the number of segments and repeaters between any two stations.

Given Data / Assumptions:

• Topology uses repeaters/hubs and coax or copper segments (not modern full-duplex switching).
• CSMA/CD timing must be preserved for reliable collision detection.
• Propagation delay across the path must remain within limits.

Concept / Approach:
The 5-4-3 rule states that along the maximum path between two stations you can have up to 5 segments connected by 4 repeaters, with at most 3 of those segments populated by active nodes (the other 2 are inter-repeater links). This bound maintains the slot-time window needed for CSMA/CD to function as specified.

Step-by-Step Solution:
1) Identify constraints: collision domains must meet round-trip timing.2) Apply the rule: ≤5 segments, ≤4 repeaters, ≤3 populated segments.3) Conclude the maximum number of segments between two nodes is five.

Verification / Alternative check:
Design guides for 10BASE5/10BASE2 and early 10BASE-T hubs cite 5-4-3 explicitly for compliant paths.

Why Other Options Are Wrong:

• Two/Three/Four/Six: these violate or understate the canonical 5-4-3 constraint for classic shared Ethernet topologies.

Common Pitfalls:
Applying this rule to switched Ethernet; with full-duplex switches, CSMA/CD no longer bounds segment counts in the same way.

Final Answer:
Five