Which bit in the IPv4 header 'Flags' field represents the DF bit?

The 'Flags' field within the IPv4 header comprises three bits that control various aspects of packet fragmentation. Among these bits, the DF bit, which stands for "Don't Fragment," is crucial in regulating how packets are handled when they traverse networks with varying Maximum Transmission Units (MTUs).

When the DF bit is set to 1, it signals that the packet must not be fragmented. If the packet encounters a network segment with a smaller MTU than the packet size, it will be dropped instead of being fragmented, prompting an ICMP error message to be sent back to the source. This functionality is essential for ensuring that packets maintain their original size and integrity, especially for certain types of data transmissions where fragmentation can be detrimental.

In the context of the Flags field, the DF bit corresponds to the second bit from the right (considering the first bit works as a reserved bit and the third bit functions as the MF, or More Fragments, flag). Therefore, it is accurately represented by the value of 1 within the three-bit Flags field. This understanding is critical when dealing with IP networking and optimizing data delivery across diversified network architectures.