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

The maximum length of the 'Options' field in an IPv4 header is indeed 320 bits, which is equivalent to 40 bytes. In the IPv4 header, the 'Options' field is variable in length and can extend the total length of the header beyond the standard 20 bytes. The header allows for a total length of up to 60 bytes, which includes both the standard 20 bytes and an additional 40 bytes for options.

To understand how this works, it's important to remember that the total header length is specified in 32-bit words. Therefore, the maximum number of 32-bit words for the IPv4 header is 15 (since the maximum header length field in the header is 15), which totals to 60 bytes (15 words x 4 bytes per word). This means that the maximum size of the Options field can reach up to 40 bytes, hence its representation as 320 bits.

The distinction of this maximum value shows how flexible the IPv4 header can be to accommodate special functionality, like security, routing information, and timestamps, which are encapsulated within the Options field when they are needed.