A network administrator is adding a new LAN to a branch office. The new LAN must support 90 connected devices. What is the smallest network mask that the network administrator can use for the new network?
- 255.255.255.128
- 255.255.255.240
- 255.255.255.248
- 255.255.255.224
Explanation: To support a LAN with 90 connected devices, the network administrator must select a subnet mask that provides a sufficient number of usable host addresses while minimizing wasted address space. The number of usable hosts is calculated using the formula 2n−2, where n represents the number of host bits remaining in the mask. A subnet mask of 255.255.255.128 (which corresponds to a /25 prefix) leaves 7 bits for the host portion, providing 126 usable host addresses. This is the most efficient (smallest) mask among the provided choices because the next tighter mask, 255.255.255.224 (/27), only provides 30 usable addresses, which is insufficient for the 90 required devices. By utilizing the /25 mask, the administrator ensures that the branch office requirements are met while adhering to the principle of maximizing available subnets by minimizing unused IP addresses.
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