Which item is contained in the Ethernet trailer?

• A. Source MAC address
• B. Destination MAC address
• C. Error-checking information
• D. EtherType field

Answer: (C)

Error detection is performed using the trailer of an Ethernet frame. The trailer contains the Frame Check Sequence (FCS), a 32-bit CRC that covers the frame’s data. As the frame is received, the NIC recalculates the CRC and compares it to the FCS at the end; if they match, the frame is considered likely error-free, and if they don’t, the frame is discarded. The header, on the other hand, carries addressing (destination and source MAC) and protocol information (EtherType), which are not part of the trailer.