The FCS is a -byte CRC (Cyclic Redundancy Check). The sender calculates it from the entire frame. The receiver recalculates and compares. If they don't match, the frame is corrupted and gets dropped silently. No retransmission happens at Layer . Higher layers like TCP must handle recovery. FCS catches transmission errors but not malicious tampering.
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$ curl repovive.com/roadmaps/network-design/physical-and-data-link-fundamentals/frame-check-sequence
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