How is the Fragment Offset field used during fragmentation?

• A. It indicates the total length of the fragment
• B. It indicates the fragment's destination address
• C. It indicates the position of the fragment data within the original packet, in 8-byte units
• D. It indicates the ID of the packet

Answer: (C)

The Fragment Offset field is all about where this piece of the original packet belongs. It tells the receiver the starting position of the fragment’s data within the original datagram, measured in 8-byte units. So, to find the actual byte offset, multiply the value by eight. This lets the receiver reassemble fragments correctly even if they arrive out of order. For example, if the first fragment carries 1000 bytes, its offset is 0; the next fragment starting at byte 1000 would have an offset of 1000/8 = 125. The first fragment usually has an offset of zero, and each subsequent fragment increases by the size of the previous fragment’s data (in 8-byte units). This is different from the total length field, which indicates how long the fragment is; the destination address field specifies where to deliver the fragment; and the Identification field links all fragments from the same original datagram.