An organization has a class B network and wishes to form subnets for 64…
2005
An organization has a class B network and wishes to form subnets for 64 departments. The subnet mask would be
- A.
255.255.0.0
- B.
255.255.64.0
- C.
255.255.128.0
- D.
255.255.252.0
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Show answer & explanation
Correct answer: D
Key idea: determine how many bits to borrow from the host portion of a Class B network to create 64 subnets.
Step 1: Start with Class B default mask = /16 (255.255.0.0).
Step 2: Find smallest n such that 2^n ≥ 64. n = 6 because 2^6 = 64.
Step 3: New prefix length = 16 + 6 = /22. Convert /22 to dotted decimal: 255.255.252.0.
Step 4: Hosts per subnet = 2^(16 - 6) - 2 = 2^10 - 2 = 1022 usable hosts.
Note on other choices: 255.255.0.0 is the default /16 (no subnets). 255.255.128.0 is /17 (only 2 subnets). 255.255.64.0 is not a valid contiguous subnet mask.
Final answer: 255.255.252.0 (/22).
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