How many total addresses are in the subnet `172.16.30.0/24`?

### Why this is right An IPv4 address contains 32 bits. A `/24` prefix fixes 24 bits for the network and leaves 8 bits for addresses within the subnet. Eight variable bits produce $2^8 = 256$ total addresses. ### The concept Slash notation gives the number of network bits, not the number of addresses. The address count is $2^{32-p}$, where $p$ is the prefix length. This question asks for total addresses, including the network and broadcast addresses. In the conventional `/24` example, those two addresses are not assigned to ordinary devices, leaving 254 usable host addresses. ### The other options - **A. 24**: This confuses the prefix length with the address count. A `/24` has 24 network bits, not 24 total addresses. - **B. 128**: This is the total size of a `/25` subnet, one bit smaller in address capacity. - **D. 512**: This is the total size of a `/23` subnet, which has one more variable bit than `/24`. ### Worked numbers - **Given**: IPv4 address length, 32 bits; prefix length, 24 bits. - **Find**: Total addresses in the subnet. - **Formula**: $2^{32-p}$, where $p$ is the number of network bits. - **Solve**: $32-24=8$ variable bits; $2^8=256$ addresses. - **Answer**: 256 total addresses. - **Check**: The `/24` block runs from `172.16.30.0` through `172.16.30.255`, which is 256 addresses. ### Terms - **IPv4**: Internet Protocol version 4, a 32-bit addressing system. - **Prefix length**: The number of leading address bits used to identify the network. - **Subnet**: A smaller logical network created from an address block. ### Remember Subtract the prefix length from 32 to find the variable bits, then calculate two to that power.