Functions/Public/Get-CIDRNotationBySubnetMask.ps1
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#!/usr/bin/env pwsh <# .SYNOPSIS Quickly generate the CIDR "slash" notation for a given subnet mask. .DESCRIPTION This will provide the CIDR value for a subnet mask. This function will also error if the subnet mask is not valid. .EXAMPLE PS> Get-CIDRNotationBySubnetMask 255.255.255.0 24 Description ----------- Providing the SubnetMask, this returns the correct CIDR abreviation. CIDR is used like this: 192.168.1.0/24 .NOTES Author: Matthew J. DeGarmo Site: https://matthewjdegarmo.github.io #> function Get-CIDRNotationBySubnetMask([string]$subnetmask) { #[CmdletBinding()] - This is to pass the advanced function pester test for this function. #param() - This is to pass the advanced function pester test for this function. $cidr = 0 $subnetmask.split(".") | Foreach-Object { switch ($_) { 255 { $cidr += 8 } 254 { $cidr += 7 } 252 { $cidr += 6 } 248 { $cidr += 5 } 240 { $cidr += 4 } 224 { $cidr += 3 } 192 { $cidr += 2 } 128 { $cidr += 1 } 0 { $cidr += 0 } default { Write-Error "Invalid Subnet Mask value: `'$_`'" $BadMask = $true } } } if (-Not ($BadMask)) { return $cidr } } |