A network administrator is adding a new LAN to a branch office. The new LAN must support 25 connected devices. What is the smallest network mask that the network administrator can use for the new network?
- 255.255.255.128
- 255.255.255.192
- 255.255.255.224
- 255.255.255.240
Explanation: To support a LAN with 25 connected devices, a network administrator must select a subnet mask that provides a sufficient number of usable host addresses while minimizing the waste of address space. The number of usable hosts is determined by the formula 2n−2, where n represents the number of host bits remaining in the mask. A subnet mask of 255.255.255.224 (which corresponds to a /27 prefix) leaves 5 bits for the host portion, allowing for 30 usable host addresses (25−2=30). This is the most efficient (smallest) block among the choices provided because the next available mask, 255.255.255.240 (/28), only provides 14 usable addresses (24−2=14), which would not accommodate the 25 required devices. By utilizing the /27 mask, the administrator ensures that the requirements of the branch office are met while adhering to the principle of maximizing available subnets by minimizing unused IP addresses.
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