To use the SO_REUSEPORT option with ASP.NET Core, you can configure the Kestrel server to enable this socket option. Here’s an example of how you can achieve this:

1. Create a custom Socket listener: You need to create a custom listener that sets the SO_REUSEPORT option.

2. Configure Kestrel to use this listener: Modify the Kestrel server options to use the custom listener.

Here’s a sample implementation:

using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Hosting;
using System;
using System.Net;
using System.Net.Sockets;
using System.Threading.Tasks;

public class Program
{
    public static void Main(string[] args)
    {
        CreateHostBuilder(args).Build().Run();
    }

    public static IHostBuilder CreateHostBuilder(string[] args) =>
        Host.CreateDefaultBuilder(args)
            .ConfigureWebHostDefaults(webBuilder =>
            {
                webBuilder.UseKestrel(options =>
                {
                    options.Listen(IPAddress.Any, 5000, listenOptions =>
                    {
                        listenOptions.UseConnectionHandler<ReusePortConnectionHandler>();
                    });
                });
                webBuilder.UseStartup<Startup>();
            });
}

public class ReusePortConnectionHandler : Microsoft.AspNetCore.Connections.ConnectionHandler
{
    public override async Task OnConnectedAsync(Microsoft.AspNetCore.Connections.ConnectionContext connection)
    {
        // Handle the connection
        await Task.CompletedTask;
    }
}

public static class ListenOptionsExtensions
{
    public static void UseConnectionHandler<T>(this ListenOptions listenOptions) where T : Microsoft.AspNetCore.Connections.ConnectionHandler
    {
        listenOptions.Use(next => async context =>
        {
            var socket = context.Features.Get<System.Net.Sockets.Socket>();
            socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, true);
            socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReusePort, true);
            await next(context);
        });
    }
}

In this example:

1. Custom Listener: The ReusePortConnectionHandler class is a placeholder where you can handle incoming connections.
2. Socket Options: The ListenOptionsExtensions class sets the SO_REUSEPORT option on the socket.
3. Kestrel Configuration: The CreateHostBuilder method configures Kestrel to use the custom listener with the SO_REUSEPORT option.

This setup allows multiple instances of your ASP.NET Core application to bind to the same port, improving load distribution and handling high concurrency.

If you have any questions or need further assistance, feel free to ask!