Which field in Ethernet frames is used to detect frame corruption?

• A. Frame Check Sequence in the header
• B. IP header checksum
• C. CRC (Cyclic Redundancy Check) field
• D. Trailer parity

Answer: (C)

Ethernet detects frame corruption using a CRC-based trailer. A 32-bit CRC value, known as the Frame Check Sequence, is calculated from the frame’s contents and appended at the end of the frame as a trailer. When a frame is received, the NIC recomputes the CRC over the received data and compares it to the FCS. If they match, the frame is considered intact; if they differ, the frame is discarded. This method catches most errors, including burst errors, with high probability.

The IP header checksum is a network-layer mechanism that protects only the IP header, not the entire Ethernet frame, so it isn’t used to detect link-layer frame corruption. The Frame Check Sequence is the correct mechanism for Ethernet error detection, though it’s located in the trailer, not the header. Trailer parity isn’t part of standard Ethernet framing.