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Spirent KB Article
Doc ID: FAQ10223
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Spirent TestCenter : Why do I see frame check sequence (FCS) error on TX port capture?
When port diagnostic loopback is set, captured TX frames show FCS error.
For the transmit packets (we can only capture control plane) we cannot verify the checksum as it is not yet added, therefore checksum error.
For the receive packets (we can capture control and data plane) we can verify the checksum as checksum has been added and checksum should be correct.
Product : Test Modules,General Navigation,L2-3,Windows GUI,Spirent TestCenter