How many bits are the total length of the IHL field in the IPv4 header?

The total length of the Internet Header Length (IHL) field in the IPv4 header is represented in 4 bits. This field specifies the size of the IPv4 header in 32-bit words. Since each word is 4 bytes, the maximum length that can be represented by the IHL field is 15 (as it can count from 0 to 15). Consequently, this translates to a maximum header size of 60 bytes (15 x 4).

When we consider the options provided and their corresponding bit sizes, it is clear that 32 bits represents the entire IPv4 header in terms of the full addressing used, but the IHL field itself only consists of those 4 bits which are relevant for indicating the length of the header. Thus, while 32 bits refers to the entire header structure, the IHL field specifically is contained within that as a smaller component, focusing on just the header length.

In summary, the IHL field effectively describes how many 32-bit words the header is made up of, but regarding its designated length, it's a maximum of 4 bits for indicating the header length.