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

    Fault : VPN errors 809, 789 and 691 -- the tunnel will not come up
    Fix   : Fix the security association -- key, certificate or service
    Source: https://jbtecwiz.com/support/win-net-vpn-809

    Run as     : Elevated PowerShell
    Expect     : 25 minutes
    Risk       : medium
    Reversible : yes

    WHEN THIS IS THE RIGHT FIX
    Error 789 or 812. The connection reaches the server and is refused at
    the IPsec layer.

    HOW TO UNDO IT
    The pre-shared key can be set back with the same command. No system
    state is changed.

    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 4"
    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 '  VPN errors 809, 789 and 691 -- the tunnel will not come up' -ForegroundColor White
Write-Host '  Fix the security association -- key, certificate or service' -ForegroundColor Cyan
Write-Host ''
Write-Host '  Risk: medium   Reversible   25 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 'Confirm the IKE services are running. 789 appears immediately if they are not.' -Command {
    Get-Service IKEEXT,PolicyAgent,RasMan | Format-Table Name,Status,StartType
}

Invoke-Step -Number 2 -Do 'For a pre-shared key profile, re-enter the key -- a trailing space pasted from an email is a genuine and frequent cause.' -Command {
    Set-VpnConnection -Name 'Work VPN' -L2tpPsk 'TheKey' -Force
}

Invoke-Step -Number 3 -Do 'For IKEv2 with certificates, check the client actually trusts the server''s issuing CA.' -Why 'An expired or missing root is the most common 789 on a rebuilt machine, and the error text never mentions certificates.' -Command {
    Get-ChildItem Cert:\LocalMachine\Root | Where-Object Subject -like '*YourCA*' | Format-List Subject,NotAfter,Thumbprint
}

Invoke-Step -Number 4 -Do 'Read what the server thought. On the RRAS server, the Security log records the SA failure with a reason.' -Command {
    Get-WinEvent -LogName Security -MaxEvents 50 | Where-Object Id -in 4653,4654 | Format-Table TimeCreated,Id,Message -Wrap
}

Write-Rule "  Confirm it worked"
Show-Prose 'The tunnel establishes and the main mode SA is listed.' 'White'
Write-Host ''
if (-not $DryRun) {
    Get-NetIPsecMainModeSA | Format-Table LocalEndpoint,RemoteEndpoint,CipherAlgorithm
}

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/win-net-vpn-809' 'Yellow'
} else {
    Write-Host '  Finished.' -ForegroundColor Green
}
Write-Host ''
Show-Prose 'To undo: The pre-shared key can be set back with the same command. No system state is changed.' 'DarkGray'
Write-Rule