Final answer:
To create eight subnets in a Class B network, we need to borrow 3 bits to extend the default subnet mask. The correct answer, given the choices, is D. 255.255.240.0 (255.255.240.0), which actually provides 16 subnets but is the only feasible option from the list that can accommodate at least eight subnets.
Step-by-step explanation:
To determine which subnet mask will provide eight subnets for a Class B network address, we need to understand how subnetting works. A Class B network has a default subnet mask of 255.255.0.0. To create subnets, we extend the subnet mask by borrowing bits from the host part of the IP address. Each bit we borrow will double the number of available subnets.
For eight subnets, we need to borrow 3 bits (since 23 = 8). Starting from the default Class B subnet mask, if we borrow 3 bits, we add them to the mask like this: 11111111.11111111.11100000.00000000, which translates to 255.255.224.0.
However, this is not one of the options provided. Among the choices given, we look for the one that aligns with 3 bits borrowed:
- A. 255.255.255.0 - This mask borrows 8 bits which is too many for just 8 subnets.
- B. 255.255.248.0 - This mask borrows 5 bits.
- C. 255.255.252.0 - This mask borrows 6 bits.
- D. 255.255.240.0 - This mask borrows 4 bits and would provide 16 subnets (24), which is more than required but the only feasible option from the list.
Therefore, the correct subnet mask to provide at least eight subnets for a Class B network, given the provided options, would be 255.255.240.0 (Option D).