What are the minimum and maximum IPv4 header lengths in bytes?

• A. Minimum 20 bytes; maximum 40 bytes.
• B. Minimum 16 bytes; maximum 64 bytes.
• C. Minimum 20 bytes; maximum 60 bytes (with options).
• D. Minimum 24 bytes; maximum 60 bytes.

Answer: (C)

IPv4 header length is determined by the Internet Header Length (IHL) field, a 4-bit value that counts how many 32‑bit words are in the header. Since the header must be at least 5 words, the minimum length is 5 × 4 = 20 bytes. The field can go up to 15 words, so the maximum length is 15 × 4 = 60 bytes, which includes up to 40 bytes of options beyond the standard 20-byte base header. So the valid range is 20 to 60 bytes, with 60 bytes representing the header that includes the maximum options. The option that states minimum 20 bytes and maximum 60 bytes (with options) is correct for this reason. Other options fall short or exceed the IHL limits (for example, 16-word minimum or 64-byte maximum would require an IHL value the 4-bit field cannot represent).