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

    Fault : Intermittent connection failures where IPv6 is half-configured
    Fix   : Change the preference, not the protocol
    Source: https://jbtecwiz.com/support/win-net-ipv6-order

    Run as     : Elevated PowerShell
    Expect     : 15 minutes
    Risk       : medium
    Reversible : yes

    WHEN THIS IS THE RIGHT FIX
    You can only change the client.

    HOW TO UNDO IT
    netsh interface ipv6 reset prefixpolicy restores the defaults.

    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 '  Intermittent connection failures where IPv6 is half-configured' -ForegroundColor White
Write-Host '  Change the preference, not the protocol' -ForegroundColor Cyan
Write-Host ''
Write-Host '  Risk: medium   Reversible   15 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 diagnosis: an IPv6 address is present but nothing IPv6 is reachable.' -Command {
    Get-NetIPAddress -AddressFamily IPv6 | Format-Table InterfaceAlias,IPAddress,PrefixOrigin
    Test-NetConnection ipv6.google.com -InformationLevel Detailed
}

Invoke-Step -Number 2 -Do 'See the current preference table.' -Command {
    Get-NetPrefixPolicy | Sort-Object Precedence -Descending
}

Invoke-Step -Number 3 -Do 'Prefer IPv4 over IPv6 without disabling IPv6.' -Why 'This raises the precedence of IPv4-mapped addresses above native IPv6, so IPv4 is tried first. It is far better than unbinding IPv6 -- several Windows components, including parts of the failover cluster and Exchange stack, expect IPv6 to exist and behave badly when it does not.' -Command {
    cmd.exe /c 'netsh interface ipv6 set prefixpolicy ::ffff:0:0/96 60 4'
}

Invoke-Step -Number 4 -Do 'Do not disable IPv6 on the adapter, and do not set DisabledComponents to 0xff. Both are widely recommended online and both cause worse problems later.' -Manual

Write-Rule "  Confirm it worked"
Show-Prose 'Connections open immediately, and IPv6 is still bound to the adapter.' 'White'
Write-Host ''
if (-not $DryRun) {
    Get-NetAdapterBinding -ComponentID ms_tcpip6 | Format-Table Name,Enabled
}

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-ipv6-order' 'Yellow'
} else {
    Write-Host '  Finished.' -ForegroundColor Green
}
Write-Host ''
Show-Prose 'To undo: netsh interface ipv6 reset prefixpolicy restores the defaults.' 'DarkGray'
Write-Rule