In an IPv4 datagram, the M bit is 0, the value of HLEN is 10, the value of…

Concept

In IPv4 fragmentation, three header fields locate a fragment's payload. The HLEN (header length) field counts the header in 4-byte words, so the header size in bytes is HLEN × 4, and the payload size is total length − header size. The fragment offset field counts in 8-byte units, so the first payload byte's sequence number is offset × 8. The M (More Fragments) bit is 0 only in the last fragment and 1 in every earlier one.

Application

1. Position from the M bit: M = 0, so this is the last fragment.

2. Header size: HLEN = 10, so header = 10 × 4 = 40 bytes.

3. Payload size: total length − header = 400 − 40 = 360 bytes.

4. First payload byte: fragment offset × 8 = 300 × 8 = 2400.

5. Last payload byte: first byte + payload − 1 = 2400 + 360 − 1 = 2759.

Cross-check

The byte span runs 2400 to 2759 inclusive, which is 2759 − 2400 + 1 = 360 bytes — exactly the payload size computed from total length minus header. The non-zero offset (2400) also confirms this is not the first fragment, and M = 0 fixes it as the last. Hence: last fragment, with first and last payload bytes 2400 and 2759.