CyberCertPrepNetwork FundamentalsIP Addressing & SubnettingEASYFree question
A lab needs to connect 6 servers with no router. What is the smallest subnet mask that provides exactly enough usable host addresses?
- A./29 (255.255.255.248): provides 2^3 - 2 = 6 usable addresses, exactly matching the requirement of 6 servers
- B./28 (255.255.255.240): provides 14 usable addresses
- C./30 (255.255.255.252): provides 2 usable addresses
- D./27 (255.255.255.224): provides 30 usable addresses
Why A is correct
Smallest subnet fitting N hosts: find the smallest power of 2 > N, then host bits = log2 of that value. 6 hosts: need 2^h - 2 >= 6, so 2^h >= 8, h=3. Prefix = 32-3 = /29. Usable = 8-2 = 6. /30 gives only 2 usable (too small). /28 gives 14 (wasteful). /29 is the exact fit. Real-world: a /29 is ideal for point-to-point or small server clusters where address conservation matters.
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