请记住，在一般情况下，您可能有多个正在进行的NAT转换，以及多个dns服务器，每个服务器都运行在不同的NAT转换级别上。

如果您有运营商级NAT，并且想与同一运营商的其他客户通信，该怎么办?在一般情况下，您永远无法确定，因为在每次NAT转换时可能会出现不同的主机名。

使用一个或多个LAN卡和虚拟机进行测试

public static string DisplayIPAddresses()
    {
        string returnAddress = String.Empty;

        // Get a list of all network interfaces (usually one per network card, dialup, and VPN connection)
        NetworkInterface[] networkInterfaces = NetworkInterface.GetAllNetworkInterfaces();

        foreach (NetworkInterface network in networkInterfaces)
        {
            // Read the IP configuration for each network
            IPInterfaceProperties properties = network.GetIPProperties();

            if (network.NetworkInterfaceType == NetworkInterfaceType.Ethernet &&
                   network.OperationalStatus == OperationalStatus.Up &&
                   !network.Description.ToLower().Contains("virtual") &&
                   !network.Description.ToLower().Contains("pseudo"))
            {
                // Each network interface may have multiple IP addresses
                foreach (IPAddressInformation address in properties.UnicastAddresses)
                {
                    // We're only interested in IPv4 addresses for now
                    if (address.Address.AddressFamily != AddressFamily.InterNetwork)
                        continue;

                    // Ignore loopback addresses (e.g., 127.0.0.1)
                    if (IPAddress.IsLoopback(address.Address))
                        continue;

                    returnAddress = address.Address.ToString();
                    Console.WriteLine(address.Address.ToString() + " (" + network.Name + " - " + network.Description + ")");
                }
            }
        }

       return returnAddress;
    }

过时了，这对我有用

public static IPAddress GetIPAddress()
{ 
 IPAddress ip = Dns.GetHostAddresses(Dns.GetHostName()).Where(address => 
 address.AddressFamily == AddressFamily.InterNetwork).First();
 return ip;
}

Imports System.Net
Imports System.Net.Sockets
Function LocalIP()
    Dim strHostName = Dns.GetHostName
    Dim Host = Dns.GetHostEntry(strHostName)
    For Each ip In Host.AddressList
        If ip.AddressFamily = AddressFamily.InterNetwork Then
            txtIP.Text = ip.ToString
        End If
    Next

    Return True
End Function

下面是同样的动作

Function LocalIP()

   Dim Host As String =Dns.GetHostEntry(Dns.GetHostName).AddressList(1).MapToIPv4.ToString

   txtIP.Text = Host

   Return True

End Function

Dns.GetHostEntry(Dns.GetHostName()).AddressList[1].MapToIPv4() //returns 192.168.14.1

当本地机器上有多个可用ip地址时，有一种更准确的方法。连接UDP套接字并读取其本地端点:

string localIP;
using (Socket socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, 0))
{
    socket.Connect("8.8.8.8", 65530);
    IPEndPoint endPoint = socket.LocalEndPoint as IPEndPoint;
    localIP = endPoint.Address.ToString();
}

Connect on a UDP socket has the following effect: it sets the destination for Send/Recv, discards all packets from other addresses, and - which is what we use - transfers the socket into "connected" state, settings its appropriate fields. This includes checking the existence of the route to the destination according to the system's routing table and setting the local endpoint accordingly. The last part seems to be undocumented officially but it looks like an integral trait of Berkeley sockets API (a side effect of UDP "connected" state) that works reliably in both Windows and Linux across versions and distributions.

因此，此方法将提供用于连接到指定远程主机的本地地址。没有建立真正的连接，因此指定的远端ip不可达。