IP datagram 20-65536 bytes 20-60 bytes Header Data VER HLEN Service type Total length 4 bits 4 bits 8 bits 16 bits Identification Flags Fragmentation offset 16 bits 3 bits 13 bits Time to live Protocol Header checksum 8 bits 8 bits 16 bits Source ip address Destination ip address Option Figure 8-2CSIE, NTUT, TAIWAN 7 Figure 8-2 IP datagram