How many addresses are in a /27?

• A. 16
• B. 64
• C. 32
• D. 128

Answer: (C)

In IPv4, the number of addresses in a subnet is determined by how many host bits are left after the prefix. A /27 leaves 5 bits for hosts (32 total bits minus 27). With 5 host bits, you can have 2^5 = 32 distinct addresses in that block. For example, a /27 like 192.168.1.0/27 runs from 192.168.1.0 through 192.168.1.31. The network address is the first address and the broadcast is the last, leaving 30 usable host addresses, but the total number of addresses in the subnet is 32.