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Networking Fundamentals · Foundational

CRC Error

An interface error counted when a received frame's FCS does not match the computed CRC, indicating corruption.

Definition

Causes include damaged or poorly terminated cables, EMI, faulty transceivers, dirty fiber connectors and duplex mismatches. CRC errors increment on the receiving interface, so the problem may be on the cable or on the far-end transmitter.

Example

A switch port with steadily increasing input errors and CRC errors is replaced with a new patch cable.

Exam tip

Rising CRC errors point to Layer 1: replace or test the cable and optics first.

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