What is the size of the FCS trailer in an Ethernet frame?

The Frame Check Sequence (FCS) trailer in an Ethernet frame is 4 bytes in size. This component plays a crucial role in error detection within the frame. When an Ethernet frame is transmitted, the sender calculates a CRC (Cyclic Redundancy Check) value based on the contents of the frame and appends this 4-byte FCS to the end of the frame.

When the receiving device gets the frame, it recalculates the CRC value and compares it to the FCS in the frame. If the two values match, it indicates that the frame was likely transmitted without errors. If they do not match, it suggests that there was an error during transmission, prompting the device to discard the frame or request a retransmission depending on the network protocol in use.

This understanding of FCS is important for recognizing how Ethernet ensures reliable data communication across networks. The other options listed do not reflect the actual size of the FCS trailer, reaffirming 4 bytes as the definitive standard.