Windows set/reset DNS servers for active network interface

get_active_network_interface_index.ps1

[int]$mainIfIndex = Get-NetRoute -DestinationPrefix '0.0.0.0/0', '::/0' |
    Sort-Object -Property { $_.InterfaceMetric + $_.RouteMetric } |
    Select-Object -First 1 | 
    % {$_.ifIndex}
    
echo $mainIfIndex

reset_DNS_servers_for_active_network_interface.bat

@echo off
FOR /F "tokens=* USEBACKQ" %%F IN (`powershell "Get-NetRoute -DestinationPrefix '0.0.0.0/0', '::/0' | Sort-Object -Property { $_.InterfaceMetric + $_.RouteMetric } | Select-Object -First 1 | %% {$_.ifIndex}"`) DO (
SET mainIfIndex=%%F
)
ECHO %mainIfIndex%

powershell "Set-DNSClientServerAddress -InterfaceIndex %mainIfIndex% -ResetServerAddresses"

ipconfig /flushdns

powershell "Get-DnsClientServerAddress -InterfaceIndex %mainIfIndex%"

pause

Set_DNS_servers_for_active_network_interface.bat

@echo off
FOR /F "tokens=* USEBACKQ" %%F IN (`powershell "Get-NetRoute -DestinationPrefix '0.0.0.0/0', '::/0' | Sort-Object -Property { $_.InterfaceMetric + $_.RouteMetric } | Select-Object -First 1 | %% {$_.ifIndex}"`) DO (
SET mainIfIndex=%%F
)
ECHO %mainIfIndex%

powershell "Set-DNSClientServerAddress -InterfaceIndex %mainIfIndex% -ServerAddresses ('1.1.1.1','1.0.0.1')"
powershell "Set-DNSClientServerAddress -InterfaceIndex %mainIfIndex% -ServerAddresses ('2606:4700:4700::1111','2606:4700:4700::1001')"

ipconfig /flushdns

powershell "Get-DnsClientServerAddress -InterfaceIndex %mainIfIndex%"

pause

File	Description
Set_DNS_servers_for_active_network_interface.bat	Set the DNS servers for the main Windows network interface to Cloudflare's servers.
reset_DNS_servers_for_active_network_interface.bat	Reset the DNS servers to the ones provided by DHCP from the network router. This is very useful for the setup of lancache.
get_active_network_interface_index.ps1	PowerShell script for determining the active network interface.

The function of the two .bat files can be implemented easier in PowerShell directly. But on some Windows machines direct execution of PowerShell script files is disabled. This is why I wrapped it all in Windows Batch files. The for-loop is only a workaround for getting the main interface index out of the PowerShell call.