What subnet mask would allow three subnetworks under specified device counts?

What subnet mask would allow three subnetworks under specified device counts?

• A. 255.255.255.0
• B. 255.255.255.240
• C. 255.255.255.128
• D. 255.255.255.224

Answer: (B)

To determine the correct subnet mask that would allow for three subnetworks, it’s important to consider how subnetting works, particularly focusing on the required number of subnets and the corresponding bits needed for that purpose. A subnet mask of 255.255.255.240 corresponds to a /28 prefix, which provides a total of 16 IP addresses. Out of these, 14 can be assigned to devices (as one address is reserved for the network and another for the broadcast). This setup allows for a maximum of 16 subnets (since 2^4 = 16, considering the 4 bits available for subnetting in the last octet) and enables the creation of multiple subnetworks. For the requirement of three subnetworks, the 255.255.255.240 mask is ideal since it allows enough flexibility to easily create three distinct subnets while still offering a generous number of usable addresses within each subnet. In contrast, other subnet masks like 255.255.255.0 (a /24 mask) would only provide one subnet for the entire Class C network, while 255.255.255.128 (a /25 mask) would allow for only two subnets, which doesn't meet the requirement.

To determine the correct subnet mask that would allow for three subnetworks, it’s important to consider how subnetting works, particularly focusing on the required number of subnets and the corresponding bits needed for that purpose.

A subnet mask of 255.255.255.240 corresponds to a /28 prefix, which provides a total of 16 IP addresses. Out of these, 14 can be assigned to devices (as one address is reserved for the network and another for the broadcast). This setup allows for a maximum of 16 subnets (since 2^4 = 16, considering the 4 bits available for subnetting in the last octet) and enables the creation of multiple subnetworks.

For the requirement of three subnetworks, the 255.255.255.240 mask is ideal since it allows enough flexibility to easily create three distinct subnets while still offering a generous number of usable addresses within each subnet.

In contrast, other subnet masks like 255.255.255.0 (a /24 mask) would only provide one subnet for the entire Class C network, while 255.255.255.128 (a /25 mask) would allow for only two subnets, which doesn't meet the requirement.