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

    Fault : AD replication error 8524 -- the DSA operation cannot continue (DNS lookup failure)
    Fix   : Fix the DC's own DNS client configuration
    Source: https://jbtecwiz.com/support/srv-ad-8524

    Run as     : Elevated PowerShell on the failing DC
    Expect     : 20 minutes
    Risk       : medium
    Reversible : yes

    WHEN THIS IS THE RIGHT FIX
    One DC cannot replicate with anything. Its own resolver settings are the
    first thing to check.

    HOW TO UNDO IT
    Put the previous DNS server addresses back with
    Set-DnsClientServerAddress.

    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 '  AD replication error 8524 -- the DSA operation cannot continue (DNS lookup failure)' -ForegroundColor White
Write-Host '  Fix the DC''s own DNS client configuration' -ForegroundColor Cyan
Write-Host ''
Write-Host '  Risk: medium   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 'Look at what the DC is using for DNS.' -Command {
    Get-DnsClientServerAddress -AddressFamily IPv4 | Format-Table InterfaceAlias, ServerAddresses -AutoSize
}

Invoke-Step -Number 2 -Do 'Correct it if wrong. A DC should point at another DC running DNS as primary, and at its own loopback as secondary -- never at itself first, and never at a public resolver.' -Why 'A DC that lists only itself can start before its own DNS service is ready and cache negative answers for the whole domain. A public resolver knows nothing about the _msdcs zone at all.' -Command {
    Set-DnsClientServerAddress -InterfaceAlias 'Ethernet' -ServerAddresses 10.0.0.11,127.0.0.1
}

Invoke-Step -Number 3 -Do 'Clear the resolver cache and re-register the DC''s records.' -Command {
    Clear-DnsClientCache
    ipconfig /registerdns
    nltest /dsregdns
}

Invoke-Step -Number 4 -Do 'Restart the Netlogon service to rewrite the SRV records.' -Command {
    Restart-Service Netlogon
}

Invoke-Step -Number 5 -Do 'Retest replication.' -Command {
    repadmin /replsummary
    repadmin /showrepl
}

Write-Rule "  Confirm it worked"
Show-Prose 'dcdiag passes its DNS and replication tests.' 'White'
Write-Host ''
if (-not $DryRun) {
    dcdiag /test:dns /v
    dcdiag /test:replications
}

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-ad-8524' 'Yellow'
} else {
    Write-Host '  Finished.' -ForegroundColor Green
}
Write-Host ''
Show-Prose 'To undo: Put the previous DNS server addresses back with Set-DnsClientServerAddress.' 'DarkGray'
Write-Rule