How many bits is the 'Fragment Offset' field in the IPv4 header?

The 'Fragment Offset' field in the IPv4 header is 13 bits in length. This field is crucial for the reassembly of fragmented packets. When a larger packet needs to be sent over a network that has a smaller Maximum Transmission Unit (MTU), the packet is divided into smaller fragments. The Fragment Offset field indicates the position or the sequence of a fragment in the original packet, allowing the receiving end to correctly reassemble all the fragments back into the original message.

This specific bit length is important because it allows for a total of 8191 different fragment offsets (2^13 - 1), which is sufficient for reassembling packets of considerable size. The choice of 13 bits balances the needs for identifying fragment positioning while also conserving header space for other fields in the IPv4 header. The other options do not accurately represent the size of this field, as they either exceed or fall short of the necessary data to handle fragmentation effectively.