More information can be found at http://tookitaway.co.uk/synchronizing-dhcp-reservations-between-two-dhcp-servers-serving-the-same-scope/

Get-UnmatchedDhcpServerv4Reservation.ps1

#Requires -Module DHCPServer

Function Get-UnmatchedDhcpServerv4Reservation {
    <#
      .Synopsis
      A function gets DHCP IPv4 reservations from a single scope stretched over two DHCP servers.

      .Description
      A function gets DHCP IPv4 reservations from a single scope stretched over two DHCP servers

      .Parameter ReferenceComputerName
      A DHCP server computer name hosting the ScopeId specified. This parameter is mandatory.

      .Parameter DifferenceComputerName
      A DHCP server computer name hosting the ScopeId specified. This parameter is mandatory.

      .Parameter ScopeId
      The ScopeID to check over the two servers to make sure that the reservations are equal. This parameter is mandatory.

      .Parameter IncludeEqual
      This switch parameter specifies whether to return results that exist on both DHCP servers and are considered equal.

      .Example
      Get-UnmatchedDhcpServerv4Reservation -ReferenceComputerName DHCP-Server-1 -DifferenceComputerName DHCP-Server-2 -ScopeId 10.0.0.0

      Returns reservation objects (like the one below) that are not specified in both DHCP servers:

        MissingOnComputer : DHCP-Server-2
        Type              : Dhcp
        ComputerName      : DHCP-Server-1
        Description       :
        ScopeId           : 10.0.0.0
        Name              : ExamplePC.whiteways.tech
        ClientId          : 00-01-23-45-67-89
        SideIndicator     : <=
        IPAddress         : 10.0.0.6

      .Notes
      Author: Information Services
    #>

    [CmdletBinding()]
    Param(
        [parameter(
            Mandatory = $True,
            Position  = 1
        )]
        [string]$ReferenceComputerName,

        [parameter(
            Mandatory = $True,
            Position  = 2
        )]
        [string]$DifferenceComputerName,

        [parameter(
            Mandatory = $True,
            Position  = 3
        )]
        [string[]]$ScopeId,

        [parameter(
            Position  = 4
        )]
        [switch]$IncludeEqual
    )

    foreach ($Scope in $ScopeId) {
        $ReferenceScope  = Get-DhcpServerv4Scope -ComputerName $ReferenceComputerName -ScopeId $Scope -ErrorAction Stop
        $DifferenceScope = Get-DhcpServerv4Scope -ComputerName $DifferenceComputerName -ScopeId $Scope -ErrorAction Stop

        If ($ReferenceScope -and $DifferenceScope)
        {
            $Referencev4Reservation = Get-DhcpServerv4Reservation -ScopeId $ReferenceScope.ScopeId -ComputerName $ReferenceComputerName -ErrorAction Stop
            $Differencev4Reservation = Get-DhcpServerv4Reservation -ScopeId $DifferenceScope.ScopeId -ComputerName $DifferenceComputerName -ErrorAction Stop

            $Placeholder = @{
                IPAddress   = $null
                ScopeId     = $null
                ClientId    = $null
                Name        = $null
                Type        = $null
                Description = $null
            }

            if (-not $Referencev4Reservation) {
                $Referencev4Reservation = New-Object -TypeName PSObject -Property $Placeholder
            }

            if (-not $Differencev4Reservation) {
                $Differencev4Reservation = New-Object -TypeName PSObject -Property $Placeholder
            }

            if ($IncludeEqual) {
                $Comparison = Compare-Object -ReferenceObject $Referencev4Reservation -DifferenceObject $Differencev4Reservation -Property ClientId, IPAddress -IncludeEqual
            }

            else {
                $Comparison = Compare-Object -ReferenceObject $Referencev4Reservation -DifferenceObject $Differencev4Reservation -Property ClientId, IPAddress, Name, Type, Description
            }

            foreach ($Compare in $Comparison) {
                if (-not $Compare.ClientId) {
                    continue
                }

                $ComparisonObject = @{
                    ComputerName      = $null
                    MissingOnComputer = $null
                    IPAddress         = $Compare.IPAddress
                    ScopeId           = $Scope
                    ClientId          = $Compare.ClientId
                    Name              = $Compare.Name
                    Type              = $Compare.Type
                    Description       = $Compare.Description
                    SideIndicator     = $Compare.SideIndicator
                }

                if ($Compare.SideIndicator -eq '<=') {
                    $ComparisonObject.ComputerName      = $ReferenceComputerName
                    $ComparisonObject.MissingOnComputer = $DifferenceComputerName
                }

                elseif ($Compare.SideIndicator -eq '=>') {
                    $ComparisonObject.ComputerName      = $DifferenceComputerName
                    $ComparisonObject.MissingOnComputer = $ReferenceComputerName
                }

                else {
                    $ComparisonObject.ComputerName = 'Both'
                }

                New-Object -TypeName PSObject -Property $ComparisonObject
            }
        }
    }
}