In the CIDR example shown, which prefix length is indicated?

In the CIDR example shown, which prefix length is indicated?

• A. /24
• B. /8
• C. /32
• D. /16

Answer: (B)

CIDR prefix length is the number of high-order bits in the IPv4 address that define the network portion. In the shown example, the network portion is eight bits, so the mask is 255.0.0.0. This fixes the first octet and leaves the remaining 24 bits for hosts, meaning the network includes addresses from x.0.0.0 to x.255.255.255 for that particular first-octet value. That is why the indicated prefix length is /8. A /24 would fix the first three octets (mask 255.255.255.0), a /16 would fix the first two octets (mask 255.255.0.0), and a /32 would fix all 32 bits to a single host address. The example shown fixes only the first octet, matching /8.

CIDR prefix length is the number of high-order bits in the IPv4 address that define the network portion. In the shown example, the network portion is eight bits, so the mask is 255.0.0.0. This fixes the first octet and leaves the remaining 24 bits for hosts, meaning the network includes addresses from x.0.0.0 to x.255.255.255 for that particular first-octet value. That is why the indicated prefix length is /8.

A /24 would fix the first three octets (mask 255.255.255.0), a /16 would fix the first two octets (mask 255.255.0.0), and a /32 would fix all 32 bits to a single host address. The example shown fixes only the first octet, matching /8.