#Requires -Version 5.1
<#
    JbTecWiz Support Centre -- generated fix script

    Fault : Clients cannot get an address -- DHCP scope exhausted or the server is not authorised
    Fix   : Re-authorise the DHCP server in Active Directory
    Source: https://jbtecwiz.com/support/srv-dhcp-exhaustion

    Run as     : Elevated PowerShell
    Expect     : 20 minutes
    Risk       : low
    Reversible : yes

    WHEN THIS IS THE RIGHT FIX
    Event 1044 or 1063 -- the service is running but deliberately not
    answering.

    HOW TO UNDO IT
    Remove-DhcpServerInDC to de-authorise.

    This script walks the fix one step at a time and asks before each
    one. Steps with no command are things you do yourself -- it prints
    those and waits. Run with -DryRun to print without executing.

    --------------------------------------------------------------------
    NO WARRANTY - USE AT YOUR OWN RISK

    This script is provided by JbTecWiz as-is and with no warranty of any
    kind, express or implied. You run it entirely at your own risk.

    JbTecWiz accepts no liability for any loss or damage arising from its
    use, including but not limited to data loss, downtime, or configuration
    changes that turn out to be wrong for your system.

    You are responsible for reading this script before running it, for
    satisfying yourself that it suits the machine in front of you, and for
    having a working backup first. Some steps cannot be undone.
    --------------------------------------------------------------------
#>

[CmdletBinding()]
param(
    # Print every step and command without running anything.
    [switch]$DryRun,
    # Do not ask before each step. Read the script first if you use this.
    [switch]$Unattended
)

$ErrorActionPreference = 'Stop'
$script:Failed = 0

function Write-Rule { param([string]$Text)
    Write-Host ''
    Write-Host ('-' * 70) -ForegroundColor DarkGray
    if ($Text) { Write-Host $Text -ForegroundColor Cyan }
}

function Show-Prose { param([string]$Text, [string]$Colour = "Gray")
    if (-not $Text) { return }
    $words = $Text -split "\s+"; $line = "  "
    foreach ($w in $words) {
        if (($line.Length + $w.Length) -gt 74) { Write-Host $line -ForegroundColor $Colour; $line = "  " }
        $line += "$w "
    }
    if ($line.Trim()) { Write-Host $line -ForegroundColor $Colour }
}

function Invoke-Step {
    param(
        [int]$Number, [string]$Do, [string]$Why,
        [scriptblock]$Command, [switch]$Manual, [string]$Shell = "powershell"
    )
    Write-Rule "  Step $Number of 5"
    Show-Prose $Do "White"
    if ($Why) { Write-Host ""; Show-Prose $Why "DarkGray" }

    if ($Manual) {
        Write-Host ''
        Write-Host '  -> Do this yourself, then press Enter to carry on.' -ForegroundColor Yellow
        if (-not $Unattended -and -not $DryRun) { [void](Read-Host) }
        return
    }

    Write-Host ''
    foreach ($l in ($Command.ToString().Trim() -split "`n")) {
        Write-Host ("    " + $l.Trim()) -ForegroundColor Green
    }
    Write-Host ''

    if ($DryRun) { Write-Host "  (dry run -- not executed)" -ForegroundColor DarkGray; return }
    if (-not $Unattended) {
        $a = Read-Host "  Run this step? [Y]es / [S]kip / [Q]uit"
        if ($a -match "^[Qq]") { Write-Host "  Stopped at your request."; exit 0 }
        if ($a -match "^[Ss]") { Write-Host "  Skipped." -ForegroundColor DarkGray; return }
    }
    try { & $Command }
    catch {
        $script:Failed++
        Write-Host ("  Step $Number failed: " + $_.Exception.Message) -ForegroundColor Red
        Show-Prose "The rest of the fix may depend on this. Read the write-up before carrying on." "Red"
        if (-not $Unattended) {
            $c = Read-Host "  Carry on anyway? [y/N]"
            if ($c -notmatch "^[Yy]") { exit 1 }
        }
    }
}

Write-Rule
Write-Host '  Clients cannot get an address -- DHCP scope exhausted or the server is not authorised' -ForegroundColor White
Write-Host '  Re-authorise the DHCP server in Active Directory' -ForegroundColor Cyan
Write-Host ''
Write-Host '  Risk: low   Reversible   20 minutes'
Write-Host ''
Show-Prose 'No warranty. Use at your own risk - JbTecWiz accepts no liability. Read it before you run it, and have a backup.' 'DarkYellow'
Write-Rule

if (-not $Unattended -and -not $DryRun) {
    $go = Read-Host '  Ready? [y/N]'
    if ($go -notmatch "^[Yy]") { Write-Host "  Nothing was changed."; exit 0 }
}

Invoke-Step -Number 1 -Do 'List the servers Active Directory has authorised.' -Why 'A Windows DHCP server in a domain refuses to lease addresses unless it finds itself in this list. It is a rogue-server protection, and it fails closed.' -Command {
    Get-DhcpServerInDC | Format-Table DnsName, IPAddress -AutoSize
}

Invoke-Step -Number 2 -Do 'Authorise it if it is missing.' -Command {
    Add-DhcpServerInDC -DnsName dhcp01.example.local -IPAddress 10.0.0.20
}

Invoke-Step -Number 3 -Do 'Confirm the server can reach a DC -- 1063 means it could not.' -Command {
    nltest /dsgetdc:example.local
    Test-NetConnection dc01.example.local -Port 389
}

Invoke-Step -Number 4 -Do 'Restart the service.' -Command {
    Restart-Service DHCPServer
}

Invoke-Step -Number 5 -Do 'Confirm the bindings are on the right interface -- a server with a second NIC often binds to the wrong one.' -Command {
    Get-DhcpServerv4Binding | Format-Table InterfaceAlias, IPAddress, BindingState -AutoSize
}

Write-Rule "  Confirm it worked"
Show-Prose 'The service stays running and clients receive leases.' 'White'
Write-Host ''
if (-not $DryRun) {
    Get-DhcpServerv4Statistics | Format-List TotalScopes, TotalAddresses, AddressesInUse, Acks
}

Write-Rule
if ($script:Failed -gt 0) {
    Write-Host ("  Finished with " + $script:Failed + " failed step(s).") -ForegroundColor Yellow
    Show-Prose 'Read the full write-up at https://jbtecwiz.com/support/srv-dhcp-exhaustion' 'Yellow'
} else {
    Write-Host '  Finished.' -ForegroundColor Green
}
Write-Host ''
Show-Prose 'To undo: Remove-DhcpServerInDC to de-authorise.' 'DarkGray'
Write-Rule