The first four IP addresses and the last IP address in each subnet CIDR block are not available for you to use, and cannot be assigned to an instance (total 5 IP reserved). For example, in a subnet with CIDR block 10.0.0.0/24, the following five IP addresses are reserved: 10.0.0.0, 10.0.0.1, 10.0.0.2, 10.0.0.3, 10.0.0.255