Which CIDR notation represents 512 addresses?

The CIDR notation that represents 512 addresses is indeed /23. To understand why this is the correct choice, it's important to know how CIDR notation works in relation to IP addresses.

CIDR (Classless Inter-Domain Routing) notation conveys the size of the subnet based on the number of bits allocated for the network portion of the address. An IPv4 address consists of 32 bits in total. The CIDR notation follows the format /X, where X represents the number of bits used for the network prefix, leaving the remaining bits for host addresses.

In the case of /23, you have 23 bits for the network portion and 9 bits remaining for host addresses (32 - 23 = 9). The number of available addresses can be calculated using the formula 2^number_of_host_bits. In this case, it would be:

2^9 = 512 addresses.

This includes both usable and reserved addresses, such as the network and broadcast addresses, thus confirming that a /23 subnet can indeed accommodate 512 total addresses.

In contrast, for /22, there are only 10 bits available for hosts (32 - 22 = 10), leading to 2^10 = 1024 total addresses.