IPv4 Header. Notes. The Internet Protocol (IPv4) is defined in RFC 791 which specifies the format of the header.; IHL (Internet Header Length) is 4 bits long and specifies the header length in increments of 32 bits (DWORD). The IHL field can hold values from 0 (Binary 0000) to 15 (Binary 1111).So the longest the IP header size can be is upto 480 bits, which is 60 bytes.

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