Check Internet Connectivity

How to check is your PC/ Server is connected to the internet.... there are more than one ways to do that - using wininet.dll, calling for DNS resolution, pinging a internet server, calling a web page and checking for response status and as I wanted to be sure that client is able to reach my server so put them all together.

First bit is thanks to Rydal.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime;
using System.Runtime.InteropServices;
using System.Text;
using System.Security;

namepsace TestCode {
public sealed class NetworkHandler {
        /// 

        /// Private constructor to prevent compiler from generating one
        /// since this class only holds static methods and properties
        /// 
        NetworkHandler() { }
        /// 

        /// SafeNativeMethods Class that holds save native methods 
        /// while suppressing unmanaged code security
        /// 
        [SuppressUnmanagedCodeSecurityAttribute]
        internal static class SafeNativeMethods {
            // Extern Library
            // UnManaged code - be careful.
            [DllImport("wininet.dll", CharSet = CharSet.Auto)]
            [return: MarshalAs(UnmanagedType.Bool)]
            private extern static bool InternetGetConnectedState(out int Description, int ReservedValue);
            /// 

            /// Determines if there is an active connection on this computer
            /// 
            /// 
            public static bool HasActiveConnection() {
                int desc;
                return InternetGetConnectedState(out desc, 0);
            }
        }
    }
}

and the function to check the connectivity

 
#region checkConnectivity
public bool CheckInternetConnection() {
	bool isInternetOn = false;
	isInternetOn = NetworkHandler.SafeNativeMethods.HasActiveConnection();
	if(isInternetOn) {
		try {
			IPHostEntry obj = Dns.GetHostEntry(strServer);
			isInternetOn = true;
		} catch {
			isInternetOn = false; // host not reachable. 
		}
	}
	if(isInternetOn) {
		try {
			HttpWebRequest reqFP = (HttpWebRequest) HttpWebRequest.Create(strServer);
			HttpWebResponse rspFP = (HttpWebResponse) reqFP.GetResponse();
			if(HttpStatusCode.OK == rspFP.StatusCode) {
				// HTTP = 200 - Internet connection available, server online
				rspFP.Close();
				isInternetOn = true;
			} else {
				// Other status - Server or connection not available
				rspFP.Close();
				isInternetOn = false; // host not reachable. 
			}
		} catch(WebException) {
			// Exception - connection not available
			isInternetOn = false; // host not reachable. 
		}
	}
	return isInternetOn;
}
#endregion