Question

I am writing a piece of software in C# using .NET 2 which detects whether there is an active ethernet connection on the Windows machine.

It is important that it knows that it is ethernet rather than WiFi as the program will behave differently depending on whether sending data with a WebClient is going over WiFi or Ethernet.

I have tried using System.Net.NetworkInformation.NetworkInterfaceType but this seems to report ‘Ethernet’ for a lot of WiFi cards.

Any suggestions will be much appreciated.

Answer 1

According to this MSDN page about the NetworkInterface.NetworkInterfaceType property,

This property only returns a subset of
the possible values defined in the
NetworkInterfaceType enumeration. The
possible values include the following:

Ethernet Fddi Loopback Ppp Slip TokenRing Unknown

So deterministically you may be SOL.

However, you may be able to perform some heuristics on the available network connections, to determine if they are WiFi or cable. These might include ping response/latency times taken over many iterations, etc.

Also, the speed of the adapter might be used as a hint. For my WiFi adapter the speed is always shown as “54000000” (e.g. 54 mbs). Since there is a set of common WiFi speeds, this could be helpful.

Perhaps the following code might get you started:

using System;
using System.Net.NetworkInformation;
using System.Net;

namespace ConsoleApplication7
{
    class Program
    {
        static void Main(string[] args)
        {
            NetworkInterface[] adapters = NetworkInterface.GetAllNetworkInterfaces();
            Ping pingObj = new Ping();

            for (int i = 0; i < adapters.Length; i++)
            {
                Console.WriteLine("Network adapter: {0}", adapters[i].Name);
                Console.WriteLine("    Status:            {0}", adapters[i].OperationalStatus.ToString());
                Console.WriteLine("    Interface:         {0}", adapters[i].NetworkInterfaceType.ToString());
                Console.WriteLine("    Description:       {0}", adapters[i].Description);
                Console.WriteLine("    ID:                {0}", adapters[i].Id);
                Console.WriteLine("    Speed:             {0}", adapters[i].Speed);
                Console.WriteLine("    SupportsMulticast: {0}", adapters[i].SupportsMulticast);
                Console.WriteLine("    IsReceiveOnly:     {0}", adapters[i].IsReceiveOnly);
                Console.WriteLine("    MAC:               {0}", adapters[i].GetPhysicalAddress().ToString());
                if (adapters[i].NetworkInterfaceType != NetworkInterfaceType.Loopback)
                {
                    IPInterfaceProperties IPIP = adapters[i].GetIPProperties();
                    if (IPIP != null)
                    {
                        // First ensure that a gateway is reachable:
                        bool bGateWayReachable = false;
                        foreach (GatewayIPAddressInformation gw in IPIP.GatewayAddresses)
                        {
                            Console.WriteLine("    Gateway:     {0} - ", gw.Address.ToString());

                            // TODO: Do this many times to establish an average:
                            PingReply pr = pingObj.Send(gw.Address, 2000);

                            if (pr.Status == IPStatus.Success)
                            {
                                Console.WriteLine("    reachable ({0}ms)", pr.RoundtripTime);
                                bGateWayReachable = true;
                                break;
                            }
                            else
                                Console.WriteLine("    NOT reachable");
                        }
                        // Next, see if any DNS server is available. These are most likely to be off-site and more highly available.
                        if (bGateWayReachable == true)
                        {
                            foreach (IPAddress ipDNS in IPIP.DnsAddresses)
                            {
                                Console.WriteLine("    DNS:         {0} - ", ipDNS.ToString());
                                PingReply pr = pingObj.Send(ipDNS, 5000); // was 2000, increased for Cor in UK office
                                if (pr.Status == IPStatus.Success)
                                {
                                    Console.WriteLine("    reachable ({0}ms)", pr.RoundtripTime);
                                    Console.WriteLine("    --- SUCCESS ---");
                                    break;
                                }
                                else
                                    Console.WriteLine("    NOT reachable");
                            }
                        }
                    } // if (IPIP != null)
                }
            } // foreach (NetworkInterface n in adapters)

            Console.ReadLine();
        }
    }
}