Explain CIDR notation and calculate the number of usable hosts in a /24 subnet.

Explain CIDR notation and calculate the number of usable hosts in a /24 subnet.

• A. CIDR uses a color-coded mask; /24 yields 1024 usable hosts.
• B. CIDR uses a decimal length; /24 yields 512 usable hosts.
• C. CIDR uses a /prefix length; /24 yields 2^(32-24) - 2 = 254 usable hosts.
• D. CIDR uses an octet count; /24 yields 16 usable hosts.

Answer: (C)

CIDR notation shows how many leading bits are fixed as the network portion, using a slash and a prefix length. In IPv4, addresses are 32 bits, so the number of usable host addresses in a subnet is 2^(32 − prefix) minus 2 (subtracting the network and broadcast addresses). For a /24, the prefix is 24, leaving 8 host bits. That gives 2^8 = 256 total addresses in the subnet, and after removing the network and broadcast addresses, 256 − 2 = 254 usable hosts. A /24 also corresponds to the familiar subnet mask 255.255.255.0. The other options misstate how CIDR works or the math: CIDR isn’t color-coded or based on decimal length or octet count, and the resulting usable host counts shown don’t match the 8 host bits of a /24.

CIDR notation shows how many leading bits are fixed as the network portion, using a slash and a prefix length. In IPv4, addresses are 32 bits, so the number of usable host addresses in a subnet is 2^(32 − prefix) minus 2 (subtracting the network and broadcast addresses). For a /24, the prefix is 24, leaving 8 host bits. That gives 2^8 = 256 total addresses in the subnet, and after removing the network and broadcast addresses, 256 − 2 = 254 usable hosts. A /24 also corresponds to the familiar subnet mask 255.255.255.0. The other options misstate how CIDR works or the math: CIDR isn’t color-coded or based on decimal length or octet count, and the resulting usable host counts shown don’t match the 8 host bits of a /24.