What is CRC used for in the data link layer?

• A. CRC is a type of encryption used to protect the payload.
• B. CRC is an error-detection code used to verify frame integrity.
• C. CRC determines the MTU.
• D. CRC identifies the source MAC address.

Answer: (B)

CRC is a method for detecting errors in data as it moves across the data link layer. A CRC value is computed from the frame’s contents and appended to the frame (as the Frame Check Sequence). When the frame arrives, the receiver recalculates the CRC from the received data and compares it to the transmitted CRC. If they match, the frame is considered intact; if they don’t, the frame is discarded or flagged for error handling. This helps catch accidental changes, including burst errors, without providing encryption or affecting how large a frame can be (MTU) or which device’s MAC address is used. In Ethernet, the Frame Check Sequence is a CRC value, typically CRC-32, used precisely for this purpose.