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Zorluk: OrtaPlanning Virtual Private Cloud (VPC) Networks and Subnets

A network engineering team is managing a custom-mode Virtual Private Cloud (VPC) network in Google Cloud. An existing primary subnet located in the `us-central1` region is currently assigned the primary IPv4 CIDR range 172.16.16.0/22172.16.16.0/22. Due to rapid workload scaling, the team needs to double the IP address capacity of this primary subnet without recreating the subnet or disrupting existing Virtual Machines (VMs). A secondary peered network occupies the range 172.16.24.0/22172.16.24.0/22. Which expanded IPv4 CIDR range should the team configure for the subnet?

  1. 172.16.16.0/21172.16.16.0/21Cevap
  2. B
    172.16.16.0/20172.16.16.0/20
  3. C
    172.16.18.0/21172.16.18.0/21
  4. D
    172.16.20.0/22172.16.20.0/22

Cevap

The primary CIDR range should be expanded to 172.16.16.0/21172.16.16.0/21.
Expanding the primary IPv4 CIDR range to 172.16.16.0/21172.16.16.0/21 correctly doubles the subnet size (from 1,024 to 2,048 addresses) without changing the starting network address. It satisfies netmask boundary alignment rules (16(mod8)=016 \pmod 8 = 0) and finishes at 172.16.23.255172.16.23.255, ensuring zero overlap with the adjacent peered range starting at 172.16.24.0/22172.16.24.0/22.

Adım Adım Çözüm

1
Determine the required IP address capacity.
The existing range 172.16.16.0/22172.16.16.0/22 provides 1,024 addresses (172.16.16.0172.16.16.0 to 172.16.19.255172.16.19.255). Doubling capacity requires a /21 prefix length (2,048 addresses).
Decreasing the CIDR prefix length by 1 bit doubles the number of available host addresses.
2
Validate the CIDR netmask boundary alignment for the expanded range.
A /21 prefix requires the third octet to be a multiple of 8. Since 16 is divisible by 8 (16=2×816 = 2 \times 8), 172.16.16.0/21172.16.16.0/21 is a valid network boundary covering 172.16.16.0172.16.16.0 to 172.16.23.255172.16.23.255.
GCP subnet expansions must maintain the existing start IP address or expand backwards to a valid CIDR boundary that encompasses the current range.
3
Check for IP address space conflicts with existing peered networks.
The expanded range (172.16.16.0172.16.16.0 – 172.16.23.255172.16.23.255) ends immediately before 172.16.24.0/22172.16.24.0/22, avoiding any overlap.
Subnet ranges in Google Cloud VPC networks cannot overlap with connected peered VPC networks or hybrid interconnect routes.

Anahtar Kavram

VPC Subnet Primary IPv4 Range Expansion Rules
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Konular

Planning Virtual Private Cloud (VPC) Networks and Subnets

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