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Zorluk: OrtaIPv4 Addressing and Subnetting

A network engineer is provisioning an IP subnet for a server pool that requires static assignment for exactly 255255 usable host IP addresses. Which Classless Inter-Domain Routing (CIDR) prefix represents the most space-efficient subnet mask that accommodates all required host addresses?

  1. /23Cevap
  2. B
    /24
  3. C
    /25
  4. D
    /22

Cevap

The prefix /23 is the most space-efficient CIDR mask.
To determine the required CIDR prefix, calculate the number of host bits nn such that 2n−2≥2552^n - 2 \ge 255. With 8 host bits (/24 prefix), the usable host capacity is 28−2=2542^8 - 2 = 254, which falls short by 1 host address. Therefore, 9 host bits are required (32−9=/2332 - 9 = /23), providing 29−2=5102^9 - 2 = 510 usable host IP addresses. This is the smallest prefix length (most space-efficient) that satisfies the requirement.

Adım Adım Çözüm

1
Determine the required host count formula.
Usable hosts per subnet = 2n−22^n - 2, where nn is the number of host bits.
Two IP addresses in every IPv4 subnet are reserved for the network ID and broadcast address.
2
Evaluate the capacity of a /24 subnet mask.
For /24, host bits n=32−24=8n = 32 - 24 = 8. Usable hosts = 28−2=256−2=2542^8 - 2 = 256 - 2 = 254.
Since 254 usable hosts is less than the required 255, a /24 prefix is insufficient.
3
Evaluate the capacity of a /23 subnet mask.
For /23, host bits n=32−23=9n = 32 - 23 = 9. Usable hosts = 29−2=512−2=5102^9 - 2 = 512 - 2 = 510.
Since 510 usable hosts is greater than or equal to 255, a /23 prefix fulfills the requirement with minimal wasted address space.

Anahtar Kavram

IPv4 CIDR Subnetting and Usable Host Calculation
Tahmini Süre:1m 15s
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Konular

IPv4 Addressing and Subnetting

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