How to configure wifi like an airport ?

I think you can not perform this action. Unless your WiFi router provides a notification to your computer that a new device has connected there is no way to tell that it has occurred - and that mechanism would differ from router to router. You could scan for new IP addresses and check if they are on WiFi, but that's about all - and it would have to be scanning pretty fast and often to spot it in time to do anything. Then there is the other half of the problem: you can't run a "login" app on "any" machine that connects: it could be iOS, Android, Linus, Windows, ... and not all of those can natively run .NET apps at all. What if it's a fridge? A toaster? Some other IoT device? That's how the WiFi password is there for: to keep "unwanted" devices out of your network. To differentiate Internet and Intranet user, you can use this : This is code from Default.aspx <%@ Page Language="C#" MasterPageFile="~/MasterPage.master" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" Title="??????" %> But this is code from codebehind file Default.aspx.cs using System; using System.Collections; using System.Configuration; using System.Data; using System.Linq; using System.Web; using System.Web.Security; using System.Web.UI; using System.Web.UI.HtmlControls; using System.Web.UI.WebControls; using System.Web.UI.WebControls.WebParts; using System.Xml.Linq; public partial class _Default : System.Web.UI.Page {     protected void Page_Load(object sender, EventArgs e)     {         string strUserIP = Page.Request.UserHostAddress;         if (strUserIP.Contains("192.168.1"))             Server.Transfer("IntranetUsers.aspx", true);         else             Server.Transfer("InternetUsers.aspx", true);     } }