Windows Monitor - DNS Servers Script

<#
This resource is provided as a convenience for Level users. We cannot 
guarantee it will work in all environments. Please test before deploying 
to your production environment. We welcome contributions to our community 
library

Level Library
https://level.io/library/script-windows-monitor-dns-servers
#>

# Comma-separated list of expected DNS servers
$allowedDnsServers = "{{cf_dns}}"

# Convert the comma-separated string into an array
$allowedDnsServersArray = $allowedDnsServers -split "\s*,\s*"

# -----------------------------------------------------------------------------

# Function to check if the DNS servers match the allowed list
function Check-DnsServers {
    $networkInterfaces = Get-WmiObject -Class Win32_NetworkAdapterConfiguration | Where-Object { $_.IPEnabled }

    foreach ($interface in $networkInterfaces) {
        $dnsServers = $interface.DNSServerSearchOrder

        Write-Host "Interface: $($interface.Description)"
        Write-Host "Allowed DNS servers: $($allowedDnsServersArray -join ', ')"
        Write-Host "Current DNS servers: $($dnsServers -join ', ')"

        if ($dnsServers -ne $null -and $dnsServers.Count -gt 0) {
            $matchingServers = @($dnsServers | Where-Object { $allowedDnsServersArray -contains $_ })

            if ($matchingServers.Count -eq $dnsServers.Count) {
                Write-Host "SUCCESS: DNS servers match the allowed list."
                exit 0
            } else {
                Write-Host "ALERT: Not all DNS servers are in the allowed list."
                exit 1
            }
        } else {
            Write-Host "ALERT: No DNS servers configured"
            exit 0
        }
    }
}

# Check if the DNS servers match the allowed list
Check-DnsServers