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Does a switch calculate the Frame check sequence (FCS) before sending packets? Because packet shouldn't change, so FCS should also stay the same.

sebix
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RebelUA
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2 Answers2

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No; as you noted the packet passes from switch to switch unchanged, so the original FCS computed by the sending station does not need to be recomputed. It does however, have to be verified that it is correct and if not, the packet is discarded rather than forwarded.

psusi
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If it is a router, the frame data is changed because the TTL and header checksum in IP header are modified.

Guy Saadon
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