Question

In an IPv4 datagram, the M bit is 0, the value of HLEN is 10, the value of total length is 400 and the fragment offset value is 300. The position of the datagram, the sequence numbers of the first and the last bytes of the payload, respectively are
1. Last fragment, 2400 and 2789
2. First fragment, 2400 and 2759
3. Last fragment, 2400 and 2759
4. Middle fragment, 300 and 689

Answer 1

Correct Answer - Option 3 : Last fragment, 2400 and 2759

The correct answer is option 3

EXPLANATION:

In the question given that M bit is 0, it means that no more fragments remaining to send after this fragment, hence this is the last fragment.

So the answer should be either option 1 or option 3

Let's check

the value of HLEN is 10 × 4 =40B because the scaling factor is 4 byte for the field,

Total length is given that is 400B

Payload size =Total length - header length

Payload size = 400B - 40B

Payload size = 360B

Fragment offset = 300 × 8 =2400B, where 8 is the scaling factor

Value of the first byte for this last fragment =2400

and the last byte is =2400 +360 -1 = 2759, here we subtract -1 because start the byte from 0

So the correct answer is option 3