When is the MF bit set to 1 in the IPv4 header?

In the IPv4 header, the More Fragments (MF) bit is set to 1 when there are more fragments to follow the current packet. This indicates that the packet has been fragmented and that the receiver should expect additional fragments that belong to the same original packet.

When a packet is larger than the Maximum Transmission Unit (MTU) of a network segment, it may need to be split into smaller packets, called fragments, for transmission. The MF bit serves a critical role in reconstructing the original packet at the destination. If this bit is set to 1, it tells the receiving device that this is not the last fragment, and there are more pieces of the packet on the way. Once the final fragment is received, it will have the MF bit set to 0, indicating that all fragments have been received.

In contrast, when fragmentation is not required, the MF bit would not be set, and the packet would be transmitted in its entirety without needing fragmentation. Similarly, if a packet is the last fragment, the MF bit would be set to 0 to indicate that no further fragments will follow. If a packet is not fragmented at all, the MF bit would also not be set, as all data can fit within a single