What is the length of the 'Identification' field in an IPv4 header?

The 'Identification' field in an IPv4 header is 16 bits long. This field is used primarily for uniquely identifying the fragments of an original IPv4 datagram. When a large packet is fragmented into smaller pieces for transmission, the Identification field helps to reassemble these fragments at the destination. Each fragment of the same original packet will carry the same value in the Identification field, ensuring that they can be correctly identified and reassembled by the receiving device.

Options indicating different lengths for this field, such as 8 bits, 12 bits, or 32 bits, do not align with the defined structure of an IPv4 header, where the Identification field is specifically allocated 16 bits. Understanding the specific lengths and functionalities of various fields in the IPv4 header is crucial for networking professionals and is a fundamental aspect of networking protocols studied in the CCNA curriculum.