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Networking Fundamentals · Intermediate

Late Collision

A collision detected after the first 64 bytes of a frame have been transmitted.

Definition

In properly built half-duplex Ethernet, collisions are detected within the first 512 bits; late collisions mean the cable is too long or, most often, a duplex mismatch where one side is full duplex. Late collisions are not automatically retransmitted by the NIC.

Example

show interfaces reporting late collisions on the half-duplex side of a link indicates a duplex mismatch.

Exam tip

Late collisions = duplex mismatch or excessive cable length.

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