How to check if a computer is responding from C#

Question

What is the easiest way to check if a computer is alive and responding (say in ping/NetBios)? I'd like a deterministic method that I can time-limit.

One solution is simple access the share (File.GetDirectories(@"\compname")) in a separate thread, and kill the thread if it takes too long.

Answer 1

Easy! Use System.Net.NetworkInformation namespace's ping facility!

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

Answer 2

To check a specific TCP port (myPort) on a known server, use the following snippet. You can catch the System.Net.Sockets.SocketException exception to indicate non available port.

using System.Net;
using System.Net.Sockets;
...

IPHostEntry myHostEntry = Dns.GetHostByName("myserver");
IPEndPoint host = new IPEndPoint(myHostEntry.AddressList[0], myPort);

Socket s = new Socket(AddressFamily.InterNetwork,
    SocketType.Stream, ProtocolType.Tcp);
s.Connect(host);

Further, specialized, checks can try IO with timeouts on the socket.

Answer 3

As long as you want to check a computer within the own subnet you could check it using ARP. Here's an example:

    //for sending an arp request (see pinvoke.net)
    [DllImport("iphlpapi.dll", ExactSpelling = true)]
    public static extern int SendARP(
                                        int DestIP, 
                                        int SrcIP, 
                                        byte[] pMacAddr, 
                                        ref uint PhyAddrLen);


    public bool IsComputerAlive(IPAddress host)
    {
        //can't check the own machine (assume it's alive)
        if (host.Equals(IPAddress.Loopback))
            return true;

        //Prepare the magic

        //this is only needed to pass a valid parameter
        byte[] macAddr = new byte[6];
        uint macAddrLen = (uint)macAddr.Length;

        //Let's check if it is alive by sending an arp request
        if (SendARP((int)host.Address, 0, macAddr, ref macAddrLen) == 0)
            return true; //Igor it's alive!

        return false;//Not alive
    }

See Pinvoke.net for more information.