#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   : Reclaim addresses and right-size the lease
    Source: https://jbtecwiz.com/support/srv-dhcp-exhaustion

    Run as     : Elevated PowerShell on the DHCP server
    Expect     : 30 minutes
    Risk       : medium
    Reversible : yes

    WHEN THIS IS THE RIGHT FIX
    The scope is full.

    HOW TO UNDO IT
    Set-DhcpServerv4Scope with the previous LeaseDuration and range.

    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 6"
    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 '  Reclaim addresses and right-size the lease' -ForegroundColor Cyan
Write-Host ''
Write-Host '  Risk: medium   Reversible   30 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 'Look at the utilisation across every scope.' -Command {
    Get-DhcpServerv4ScopeStatistics | Format-Table ScopeId, Free, InUse, PercentageInUse -AutoSize
}

Invoke-Step -Number 2 -Do 'See what is actually holding the leases.' -Command {
    Get-DhcpServerv4Lease -ScopeId 10.0.10.0 | Group-Object AddressState | Format-Table Count, Name -AutoSize
    Get-DhcpServerv4Lease -ScopeId 10.0.10.0 | Sort-Object LeaseExpiryTime | Select-Object -First 20 IPAddress, HostName, ClientId, LeaseExpiryTime
}

Invoke-Step -Number 3 -Do 'Shorten the lease so transient devices release addresses quickly. Eight hours suits guest and Wi-Fi populations far better than the 8-day default.' -Why 'Shortening the lease does not free anything immediately -- existing leases run to their expiry. It stops the problem recurring rather than solving today''s outage.' -Command {
    Set-DhcpServerv4Scope -ScopeId 10.0.10.0 -LeaseDuration 08:00:00
}

Invoke-Step -Number 4 -Do 'For immediate relief, extend the address range if the subnet has room.' -Command {
    Set-DhcpServerv4Scope -ScopeId 10.0.10.0 -StartRange 10.0.10.20 -EndRange 10.0.10.250
}

Invoke-Step -Number 5 -Do 'Remove leases for devices that are long gone.' -Command {
    Get-DhcpServerv4Lease -ScopeId 10.0.10.0 | Where-Object { $_.AddressState -eq 'Declined' } | Remove-DhcpServerv4Lease
}

Invoke-Step -Number 6 -Do 'Turn on conflict detection so a duplicate address does not silently poison the pool.' -Command {
    Set-DhcpServerSetting -ConflictDetectionAttempts 1
}

Write-Rule "  Confirm it worked"
Show-Prose 'Free addresses are available and clients get a lease.' 'White'
Write-Host ''
if (-not $DryRun) {
    Get-DhcpServerv4ScopeStatistics | Format-Table ScopeId, Free, PercentageInUse -AutoSize
}

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: Set-DhcpServerv4Scope with the previous LeaseDuration and range.' 'DarkGray'
Write-Rule