CIDR Continued
To determine the subnet of the address 192.168.4.30/28, you must first determine the binary value of the lowest masking bit. In this case, it is16.
So, the first valid range of host identifiers is on subnet 192.168.4.16 and includes the host addresses 192.168.4.17 – 192.168.4.30; this means that 192.168.4.30/28 is a host on subnet 192.168.4.16.
Remember, the last address before the next subnet is a broadcast. In our example, the address 192.168.4.31/28 would be a broadcast for subnet 192.168.4.16.
192.168.4.31 is not a valid host identifier because the number 31 requires that the host portion (last four digits) is all ones.