Which statement best describes the IPv4 address space size?

• A. 4.3 billions
• B. 6 billions
• C. 4.0 billions
• D. 3.5 billions

Answer: (A)

IPv4 addresses are 32 bits long, so the total number of possible addresses is 2^32. That equals 4,294,967,296, which is commonly rounded to about 4.3 billion. So describing the IPv4 address space as about 4.3 billion addresses is the most accurate summary. The other numbers are less precise or exceed the actual space: 6 billion would require more than 32 bits, 4.0 billion understates the exact total by about 294 million, and 3.5 billion is even smaller. Remember, a portion of those addresses are reserved for special purposes, but the total address space remains 4.3 billion.