Final answer:
The first subnet available for use with CIDR notation is immediately after the network address, and the last subnet is immediately before the broadcast address. For example, in the CIDR block 192.168.0.0/24, the first usable subnet is 192.168.0.1 and the last is 192.168.0.254.
Step-by-step explanation:
The first and last subnets available for use with CIDR notation can be determined by calculating the range of IP addresses within a given network. CIDR, which stands for Classless Inter-Domain Routing, is used to allocate IP addresses and manage IP routing, allowing for more efficient allocation of IP addresses. In a CIDR block, the first subnet is always the one immediately after the network address, while the last subnet is the one immediately before the broadcast address.
To illustrate, for a CIDR block like 192.168.0.0/24, the first usable subnet would be 192.168.0.1 (since 192.168.0.0 is the network address) and the last usable subnet would be 192.168.0.254 (since 192.168.0.255 is the broadcast address).