An IP router with a Maximum Transmission Unit (MTU) of 244 bytes has received an IP packet of size 1025 bytes with an IP header of length 20 bytes. Which of the following is not correct values of the relevant fields in the IP fragmentations generated by the router for this packet are:
(A) MF bit: 0, Datagram Length: 154; Offset: 112
(B) MF bit: 1, Datagram Length: 224; Offset: 56
(C) MF bit: 1, Datagram Length: 224; Offset: 84
(D) MF bit: 0, Datagram Length: 224; Offset: 112


Answer: (D)

Explanation: Since size of MTU is 244 byte and IP header is 20 byte, so Datagram Length will be 244 – 20 = 224 bytes.

There will be 4 packets of size 224 byte data and 20 bytes header. Last packet will have only 1025 – 224*4 = 154 byte of remaining data.

Kth fragmentation offset value = Fragment Size * (Kth fragment – 1) / Scaling Factor.

Therefore, values of fragment offset are 0, 28, 56, 84, and 112.

Values of more fragement (MF) will have 1 except last fragement which have 0.

Therefore, option (D) is not correct.

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