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NEXTSUBNET

nextsubnet is a tool for helping you find out what the next subnet available is in a given virtual network, specially when it already has some subnets created and you want to fill in the gaps when possible.

INSTALATION

Go to releases and download the version of you choosing.

USAGE

Usage:
  nextsubnet -n network -m mask [--ignore-list list | --ignore-file file] [flags]

Examples:
  # Find the next /24 subnet in the network 10.0.0.0/22
  # that doesn't overlap any of the two existent subnets
  nextsubnet --network 10.0.0.0/22 --subnet-mask 25 --ignore-list 10.0.0.0/24,10.0.1.128/25

  # You can also pass in a file containing the subnets in use
  nextsubnet --network 10.0.0.0/22  --subnet-mask 24 --ignore-file subnets.txt

MOTIVATION

When using the Azure Portal to provision a subnet it automatically calculates the subnet address space based on the mask you provide. On the other hand, when provisioning via az-cli, ARM Template or REST API you have to calculate the subnet range yourself.

USE CASE SCENARIO

Let's say you have the following virtual network: 10.0.0.1/22 and two subnets whithin it: 10.0.0.0/24, 10.0.1.128/25

vnet: 10.0.0.1/22
  subnet: 10.0.0.0/24
  subnet: 10.0.1.128/25

If you were to provision a /25 subnet, the next available address space would fall between the two existing ones:

vnet: 10.0.0.1/22
  subnet: 10.0.0.0/24
  subnet: 10.0.1.0/25
  subnet: 10.0.1.128/25

In the ever changing environment that is the cloud, it's often the case that a subnet is no longer needed and is eventually removed, leaving a gap. Using nextsubnet you can optimize the virtual network address space usage by filling those gaps whenever possible.

ROADMAP

📅 Upcomming features and changes can be seen at nextsubnet roadmap