5 IP – Fragment Offset

Based on RFC 791, IP provides fragmentation and reassembly of long datagrams, if necessary, for transmission through small networks.

IP fragmentation occurs datagram is broken into smaller datagram based on the maxium payload that fits in a single Ethernet frame Maximum Transmission  Unit (MTU). When a network interface card receives a IP fragment, it stores it in buffer until all the  IP fragments are received and can be reassembled to form UDP or TCP segment.