How many IPv4 addresses are available in total?

• A. 4.3 billions
• B. 4.0 billions
• C. 3.9 billions
• D. 5.0 billions

Answer: (A)

IPv4 addresses are 32 bits long, so there are 2^32 unique values. That equals 4,294,967,296 addresses in total. Rounding this gives about 4.3 billion, which is why that option is the best match for the total number of IPv4 addresses. The other numbers under- or over-estimate: 4.0 billion and 3.9 billion are lower than the exact total, and 5.0 billion is higher than the total possible with 32-bit addresses. If you were asking for usable host addresses, you’d also have to account for reserved and special ranges, but for total addresses, 4.29 billion is the correct figure.