How to permanently remove default routing rule for secondary network interface from window's IP routing table in C#

To permanently remove a default routing rule for a secondary network interface from Windows' IP routing table using C#, you can utilize the Route class from the System.Net.NetworkInformation namespace. However, note that modifying the routing table may require administrative privileges, so your application might need to run with elevated permissions.

Here's an example of how you can achieve this:

csharpCopy code
using System;

using System.Net.NetworkInformation;

using System.Net.Sockets;



class Program

{

    static void Main(string[] args)

    {

        // Specify the IP address of the secondary network interface

        string secondaryInterfaceIpAddress = "192.168.1.2";



        // Create a Route object for the default route

        Route defaultRoute = new Route(IPAddress.Parse("0.0.0.0"), IPAddress.Parse(secondaryInterfaceIpAddress));



        // Find the existing route entry for the default route

        foreach (Route route in Route.GetRoutes())

        {

            if (route.Destination.ToString() == "0.0.0.0" && route.NetworkInterface != null)

            {

                if (route.NetworkInterface.NetworkInterfaceType != NetworkInterfaceType.Loopback)

                {

                    // Remove the route

                    route.Delete();

                    Console.WriteLine("Default route removed for interface: " + route.NetworkInterface.Name);

                }

            }

        }

    }

}

Please note the following:

1. Running this code may require administrative privileges. Make sure your application is executed with elevated permissions.
2. The above code iterates through the existing routes and removes the default route associated with a network interface that isn't the loopback interface. This code assumes you want to remove the default route associated with the secondary network interface based on the IP address you provided.

Be cautious when modifying the IP routing table, as incorrect changes can disrupt network connectivity. It's recommended to test such modifications in a controlled environment before applying them to production systems.