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Zorluk: ZorIPv4 Addressing and Subnetting

A network engineer is assigned the IPv4 network block 10.140.0.0/1810.140.0.0/18 to provision subnets for standard branch offices. Each branch office requires a subnet capable of accommodating at least 110110 usable host IP addresses. What is the maximum number of equal-sized subnets supporting this host requirement that can be created from the 10.140.0.0/1810.140.0.0/18 block?

Cevap: 128 subnets

Cevap

The maximum number of valid branch subnets that can be created is 128.
To support at least 110 usable hosts per subnet, 7 host bits are required (27−2=1262^7 - 2 = 126 usable hosts). Subtracting 7 host bits from 32 total IPv4 bits results in a /25/25 prefix length. Borrowing bits from the allocated /18/18 summary block gives 25−18=725 - 18 = 7 subnet bits. Therefore, 27=1282^7 = 128 valid subnets can be created.

Adım Adım Çözüm

1
Determine the required host bits for at least 110 usable host IP addresses.
7 host bits are required because 27−2=126≥1102^7 - 2 = 126 \ge 110, whereas 6 host bits (26−2=622^6 - 2 = 62) are insufficient.
Every IPv4 subnet reserves two IP addresses for the network ID and the broadcast ID, making the usable host formula 2h−22^h - 2.
2
Determine the required CIDR prefix length for each subnet.
The prefix length is /25/25 (32−7=2532 - 7 = 25).
An IPv4 address consists of 32 bits; subtracting the 7 host bits leaves 25 network bits.
3
Calculate the number of borrowed subnet bits relative to the parent block.
7 subnet bits are borrowed (25−18=725 - 18 = 7).
Extending the parent network prefix from /18/18 to /25/25 borrows 7 bits for subnetting.
4
Calculate the total number of /25/25 subnets within the /18/18 parent block.
The total number of subnets is 27=1282^7 = 128.
Borrowing nn subnet bits yields 2n2^n distinct subnets.

Anahtar Kavram

Calculating IPv4 subnet capacity and prefix derivation based on host requirements
Tahmini Süre:2m 0s
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Konular

IPv4 Addressing and Subnetting

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