What is the maximum length of the IPv4 header?

The IPv4 header has a maximum length of 60 bytes. This is due to the fact that the header is composed of a fixed portion and an optional portion, which can extend its size. The fixed portion of the IPv4 header is 20 bytes, but the header length field, which is expressed in 32-bit words, allows for an additional 40 bytes of options, making the total possible length 60 bytes.

The header length field in the IPv4 header specifies the length of the header in 32-bit words, and it can range from a minimum of 5 (which equals 20 bytes) to a maximum of 15 (which equals 60 bytes). Each 32-bit word is 4 bytes, so when you multiply the maximum of 15 by 4, you arrive at 60 bytes.

This knowledge is crucial in networking, especially for IP packet construction and analysis, as it defines the structure and limits of how much data can be included in the header for routing and processing.