Is there something like a ssid for lan? / Can I identify the current network?

Question

I'm writing a c# program where I should compare the current network the PC is connected to with a database.

With W-LAN its easy (SSID), but how can I identify the network if the user is connected via LAN and is the SSID the best solution?

Thanks.

Answer 1

If you want to go the route of MAC for default gateway try this:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Net;
using System.Net.NetworkInformation;
using System.Net.Sockets;
using System.Runtime.InteropServices;
using System.Threading.Tasks;

namespace NetworkIdentifier
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var macAddressOfGateway = GetMacAddressOfGateway();
            Console.WriteLine(macAddressOfGateway);
            Console.ReadLine();
        }

        private static string GetMacAddressOfGateway()
        {
            var networkInterface = GetBestNetworkInterface();
            var gatewayAddress = networkInterface.GetIPProperties().GatewayAddresses.FirstOrDefault();
            if (gatewayAddress == null)
            {
                throw new InvalidOperationException("No gateway!");
            }

            var mac = GetMacAddress(gatewayAddress.Address);

            return MacToString(mac);
        }

        private static string MacToString(byte[] mac)
        {
            return string.Format("{0:X2}:{1:X2}:{2:X2}:{3:X2}:{4:X2}:{5:X2}", mac[0], mac[1], mac[2], mac[3], mac[4], mac[5]);
        }

        public static NetworkInterface GetBestNetworkInterface()
        {
            var publicIpAddress = new IPAddress(0x08080808); // Googles DNS IP of 8.8.8.8 (Seems like a relatively safe hardcoded IP to pick :))
            var ipv4AddressAsUInt32 = BitConverter.ToUInt32(publicIpAddress.GetAddressBytes(), 0);
            uint interfaceindex;
            var result = Win32ApiCalls.GetBestInterface(ipv4AddressAsUInt32, out interfaceindex);
            if (result != 0)
            {
                throw new Win32Exception(result);
            }

            var networkCards = NetworkInterface.GetAllNetworkInterfaces().Where(x => x.OperationalStatus == OperationalStatus.Up);
            return networkCards.FirstOrDefault(networkInterface => networkInterface.GetIPProperties().GetIPv4Properties().Index == interfaceindex);
        }

        public static IPAddress GetDefaultGateway()
        {
            var networkInterface = GetBestNetworkInterface();
            if (networkInterface == null) return null;
            var address = networkInterface.GetIPProperties().GatewayAddresses.FirstOrDefault();
            return address.Address;
        }

        public static byte[] GetMacAddress(IPAddress address)
        {
            byte[] mac = new byte[6];
            uint len = (uint)mac.Length;
            byte[] addressBytes = address.GetAddressBytes();
            uint dest = ((uint)addressBytes[3] << 24)
              + ((uint)addressBytes[2] << 16)
              + ((uint)addressBytes[1] << 8)
              + ((uint)addressBytes[0]);
            if (Win32ApiCalls.SendARP(dest, 0, mac, ref len) != 0)
            {
                throw new Exception("The ARP request failed.");
            }
            return mac;
        }
    }

    public static class Win32ApiCalls
    {
        [DllImport("iphlpapi.dll", CharSet = CharSet.Auto)]
        public static extern int GetBestInterface(UInt32 destAddr, out UInt32 bestIfIndex);

        [DllImport("iphlpapi.dll", ExactSpelling = true)]
        public static extern int SendARP(uint destIP, uint srcIP, byte[] macAddress, ref uint macAddressLength);
    }
}

This needs a lot of clean up, caveating, error checking, etc. (and won't work on non-windows hosts, so don't even bother with dnxcore :))

** Caveat Emptor :)

Edit: Just removed my commented out lines as they didn't add anything useful