Question

How can I know which machines are alive on the same LAN as my PC using ASP.NET?

Answer 1

You can ping the computers on the network.

// addressToPing can be an IPaddress or host name. // returns a boolean indicating successful ping public static bool PingComputer (string[] addressToPing) {     Ping pingSender = new Ping ();     PingOptions options = new PingOptions ();      // Use the default Ttl value which is 128,     // but change the fragmentation behavior.     options.DontFragment = true;      // Create a buffer of 32 bytes of data to be transmitted.     string data = 'aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa';     byte[] buffer = Encoding.ASCII.GetBytes (data);     int timeout = 120;     PingReply reply = pingSender.Send (args[0], timeout, buffer, options);     return reply.Status == IPStatus.Success; }    

http://msdn.microsoft.com/en-us/library/system.net.networkinformation.ping.aspx

You can use this ping code and iterate through the IP addresses on your LAN (for(i = 1; i < 255; i++)). You should probably read up on doing IP address calculations though:

http://blogs.msdn.com/knom/archive/2008/12/31/ip-address-calculations-with-c-subnetmasks-networks.aspx

This is called a ‘ping sweep’. It does assume that the computers on the network have not been configured to ignore ICMP requests.