CIDR Notation

Correct Answer: /29

The best CIDR notation for a subnet containing 8 IP addresses would be /29. This is because a /29 subnet provides exactly 8 IP addresses (even though 2 are reserved for network address and broadcast address, the question assumes we require 8 addresses in total, not 8 usable ones). A /28, /27 or /26 subnet provides more addresses (16, 32, and 64 respectively), which is unnecessary when you only need 8, hence wasting the IP addresses. Therefore, /29 is the most efficient and best choice.

Correct Answer: /26

CIDR notation /26 specifies a subnet that can accommodate up to 64 IP addresses, which is more than sufficient for the requirement of 50 addresses. Taking into account the network address and the broadcast address which cannot be assigned to any device, we are left with 62 usable addresses. The other choices provide either less than or excess number of addresses. For instance, /25 provides 128 addresses, which is excessive; /28 provides only 16 addresses, which is too few; and /29 provides a mere 8 addresses, still insufficient. Hence /26 is the best-suited option.

Correct Answer: /26

An IP address in CIDR notation with /24 means that the first 24 bits are used for the network, leaving 8 bits for hosts. The network can accommodate 256 addresses (calculated as 2 to the power of 8). As the requirement is for a subnet of 40 IP addresses, a /26 CIDR notation will be used. This uses the first 26 bits for the network, leaving 6 bits for hosts - providing 64 addresses (calculated as 2 to the power of 6), which is more than enough for the 40 required by the Finance department. The subnet size closest to the requirement yet larger should be chosen. A /25 would provide 128 addresses, a waste as the requirement is for only 40 addresses. A /24 would provide the entire 256 addresses, an even greater waste. On the other hand, a /29 would only provide 8 addresses, which is insufficient for the requirement.