As a system administrator, you might have to manage a Windows DHCP server and convert DHCP leases to reservations at some point. However, this can be a tedious task if you have many leases to convert. Fortunately, PowerShell can automate this process, making it much easier and faster. This post provides a step-by-step guide on how to convert DHCP leases to reservations using PowerShell.

Step 1: Open PowerShell

The first step is to open PowerShell with administrative privileges on the Windows DHCP server. You can do this by right-clicking on the PowerShell icon and selecting “Run as administrator.”

Step 2: Define the Functions

Copy and paste the following functions into PowerShell:

function Convert-DhcpLeasesToReservations
{
    param (
        [Parameter(Mandatory=$true)]
        [string]$ScopeId,

        [Parameter()]
        [switch]$WhatIf
    )

    $leases = Get-DhcpServerv4Lease -ComputerName localhost -ScopeId $ScopeId

    foreach ($lease in $leases)
    {
        $reservation = New-DhcpServerv4Reservation -IPAddress $lease.IPAddress -ClientId $lease.ClientId -ScopeId $lease.ScopeId -Description "Converted from DHCP lease"
        if (!$WhatIf) {
            Add-DhcpServerv4Reservation -ComputerName localhost -Reservation $reservation
        }
    }

    Write-Host "All DHCP leases within scope $ScopeId have been converted to reservations"
}

function Convert-DhcpLeasesToReservationsByFilter
{
    param (
        [Parameter(Mandatory=$true)]
        [string]$Filter,

        [Parameter()]
        [switch]$WhatIf
    )

    $scopes = Get-DhcpServerv4Scope -ComputerName localhost | Where-Object { $_.Name -like $Filter }

    foreach ($scope in $scopes)
    {
        Convert-DhcpLeasesToReservations -ScopeId $scope.ScopeId -WhatIf:$WhatIf
    }
}

Step 3: Run the Functions

To use these functions, you need to run Convert-DhcpLeasesToReservationsByFilter and specify the filter to select the DHCP scopes you want to convert DHCP leases to reservations. For instance, you can run:

Convert-DhcpLeasesToReservationsByFilter -Filter "192.168.*"

This command will convert all DHCP leases within the scopes that match the filter “192.168.*” to reservations.

You can also use the -WhatIf parameter to simulate the execution of the function without making any changes. This helps you to see what the function will do before actually running it. For instance, you can run:

Convert-DhcpLeasesToReservationsByFilter -Filter "192.168.*" -WhatIf

This command will display the details of the actions the function will perform, but it will not execute them.

Conclusion:

Using PowerShell to convert DHCP leases to reservations can save you time and effort. The functions provided in this blog post simplify the process, allowing you to automate the conversion of DHCP leases to reservations in a few simple steps. By following the steps outlined above, you can easily and quickly convert DHCP leases to reservations on your Windows DHCP server.