Is CRC considered data? Do sniffers capture the CRC value?

• A. No. Sniffers Do Not Capture CRC
• B. Yes, CRC is captured as data
• C. Only in promiscuous mode
• D. Only for broadcast frames

Answer: (A)

CRC, or the Frame Check Sequence, is a trailer appended to every Ethernet frame to detect transmission errors. It’s used for error checking, not as part of the actual data payload that higher layers read, so it isn’t considered data.

As for sniffers, capture software typically receives the frame contents from the NIC after the Data Link layer has prepared the frame for delivery. In most environments, the NIC or the capture driver strips off the CRC trailer before handing the frame to the sniffer, so the CRC isn’t shown as part of the captured data. Some hardware or drivers can be configured to include the FCS in captures, but that’s not the default behavior, and the CRC is not treated as data in normal operation.