SetPrimaryDNS.ps1

$desiredPrimary = "127.0.0.1"

# Get current DNS Servers
$foo = Get-DnsClientServerAddress | where { $_.InterfaceAlias -eq "Ethernet"} | ? {$_.AddressFamily -eq 2 }
$dnsServers = $foo.ServerAddresses

# Stop if primary is already localhost
if ($dnsServers[0].Equals($desiredPrimary)) {
	echo "Primary DNS Server is already set to 127.0.0.1"	
	exit 0
}

# Prepend localhost as Primary DNS Server
$newDNSServersList = New-Object 'System.Collections.Generic.List[string]'
$newDNSServersList.Add($desiredPrimary)
# Add the rest
ForEach ($dnsServer in $dnsServers) {
	$newDNSServersList.Add($dnsServer)
}

# Set the new DNS Servers list
Set-DnsClientServerAddress -InterfaceAlias "Ethernet" -ServerAddresses $newDNSServersList

echo "Done"