I am trying to understand IPv4. I cannot understand
A byte is eight bits, so a 32-bit word is four bytes. The value of the IHL field must be multiplied times four to get the length of the header in bytes. For example, you will almost always see the value of that field is
5, meaning that the header length is 20 bytes (
5 * 4 bytes = 20 bytes).
An IPv4 header is a minimum of 20 bytes, and there are options that could increase the length up to 60 bytes, but those options are rarely used, and most are blocked in modern networking. The original idea that IPv4 used has proved to be a poor design, and IPv6 was made with a fixed header size for easier and faster processing.