flag bits
There are three flag bits in the IP header: 0, Don't Fragment( DF) and More Fragments( MF). These 3 flag bits indicate whether the datagrams are fragmented or not and whether they need to be reassembled on the receiving side.
The flag bit Don't Fragment (DF) is a control character with which the sending data station determines whether a datagram may be fragmented or not fragmented on the transmission path. If the sender provides for fragmentation, the DF bit is set to "0"; if the data packet is not allowed to be fragmented, the DF bit is set to "1". If a non-fragmentable datagram arrives at a network node that cannot process it in terms of size - and is also not allowed to fragment it - the network node discards the datagram and informs the sending data station that the datagram could not be processed.
The More Fragments (MF) flag bit is an information bit that indicates that a datagram is a fragment followed by more fragments. In this case, the MF bit is set to "1". If it is the last fragment of a file, the MF bit is set to "0", which means that no more fragments will follow.