How many addresses are in a /30?

• A. 2
• B. 4
• C. 8
• D. 16

Answer: (B)

A /30 leaves only two bits for hosts, so the total number of addresses in the subnet is 2^(32-30) = 4. For example, 192.168.1.0/30 includes 192.168.1.0, 192.168.1.1, 192.168.1.2, and 192.168.1.3. The network address is 192.168.1.0 and the broadcast address is 192.168.1.3, leaving two usable addresses for devices. Since the question asks for the number of addresses in the subnet, the total is four.