Question 31
An IP packet has arrived in which the fragmentation offset value is 100, the value of HLEN is 5 and the value of total length field is 200. What is the number of the last byte?
The IPv4 fragment offset is measured in 8-byte units. The fragment begins at byte offset 100$\times 8 = 800$ in the original payload. HLEN = 5 means a 20-byte IP header, so the fragment payload length is 200-20 = 180 bytes. Numbering the first payload byte at offset 800, the last byte is 800+180-1 = 979. This assumes the question’s “byte number” refers to the original datagram payload offset numbering.