Fragment Offset
The fragment offset field is measured
in units of eight-byte blocks. It is 13 bits long and specifies the offset of a
particular fragment relative to the beginning of the original fragmented IP
datagram. The first fragment has an offset of zero. This allows a maximum
offset of (213 –
1) × 8 = 65,528 bytes, which would exceed the maximum IP packet length of
65,535 bytes with the header length included (65,528 + 20 = 65,548 bytes).
Why we need to
divide fragment offset by 8?
Total length of the
packet ( 2^16 -1) = 65535 bytes. If the fragment offset is 16 bits then we
Can keep fragment offset as it's because 2^16 bytes is
65535 (Total length of the packet)..
We can only specify
8192 bytes (2^13) as maximum value of fragment offset. Only if we multiply
8192*8=65536 we will get the total length of the packet.
So whenever we mention fragment offset we need
to divide total size of the packet by 8.
Because in case if the packet size is 65535 byes we can't mention it
because the maximum value of the fragment offset is 8192 bytes(2^13)
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