How many total addresses are in a /29 subnet?

• A. 8
• B. 6
• C. 4
• D. 16

Answer: (A)

In IPv4 subnetting, the prefix length tells you how many bits are fixed for the network; the remaining bits are for hosts. There are 32 bits in an IPv4 address, so with a /29 the host portion has 32 − 29 = 3 bits. The number of possible addresses in the subnet is 2^3, which equals 8. These eight addresses include the network address and the broadcast address, leaving six usable addresses for hosts. For example, a /29 like x.y.z.0/29 spans x.y.z.0 to x.y.z.7, where x.y.z.0 is the network address and x.y.z.7 is the broadcast address. Therefore, the total addresses in a /29 subnet are eight.