TCP/ip

Hi
i need little help here from tcp/ip experts if there is any..?
Can anybody tell me

" Why the IP version 4 fragment sizes must be a multiple of 8 Bytes" ???

thanx in advance

Though you posted in the wrong forum but i'll answer it anyway.

Multiples of 8 octets are used so that maximum-size packet of 65535 bytes can be described in 13 bits fragment-offset.