如何获得*互联网*IP？

想象一下,我有两台局域网的PC,一台连接到互联网另一台连接到本地网络,如何通过C#检测连接到互联网的IP？

试试这个:

static IPAddress getInternetIPAddress()
{
    try
    {
        IPAddress[] addresses = Dns.GetHostAddresses(Dns.GetHostName());
        IPAddress gateway = IPAddress.Parse(getInternetGateway());
        return findMatch(addresses, gateway);
    }
    catch (FormatException e) { return null; }
}

static string getInternetGateway()
{
    using (Process tracert = new Process())
    {
        ProcessStartInfo startInfo = tracert.StartInfo;
        startInfo.FileName = "tracert.exe";
        startInfo.Arguments = "-h 1 208.77.188.166"; // www.example.com
        startInfo.UseShellExecute = false;
        startInfo.RedirectStandardOutput = true;
        tracert.Start();

        using (StreamReader reader = tracert.StandardOutput)
        {
            string line = "";
            for (int i = 0; i < 9; ++i)
                line = reader.ReadLine();
            line = line.Trim();
            return line.Substring(line.LastIndexOf(' ') + 1);
        }
    }
}

static IPAddress findMatch(IPAddress[] addresses, IPAddress gateway)
{
    byte[] gatewayBytes = gateway.GetAddressBytes();
    foreach (IPAddress ip in addresses)
    {
        byte[] ipBytes = ip.GetAddressBytes();
        if (ipBytes[0] == gatewayBytes[0]
            && ipBytes[1] == gatewayBytes[1]
            && ipBytes[2] == gatewayBytes[2])
        {
            return ip;
        }
    }
    return null;
}

请注意,此实现findMatch()依赖于C类匹配.如果您想支持B类匹配,只需省略检查即可ipBytes[2] == gatewayBytes[2].

编辑历史:

更新使用www.example.com.

更新为包含getInternetIPAddress(),以显示如何使用其他方法.

FormatException如果getInternetGateway()无法解析网关IP,则更新以捕获.(如果网关路由器配置为不响应traceroute请求,则会发生这种情况.)

引用Brian Rasmussen的评论.

更新为使用www.example.com的IP,以便即使DNS服务器关闭也能正常工作.

Internet连接必须与默认网关位于同一IP网络上.

如果你能够到达"互联网",那么从IP地址无法告诉你真的万无一失.基本上,您可以与自己的IP网络进行通信.其他一切都必须通过网关.因此,如果您看不到网关,则仅限于本地IP网络.

但是,网关依赖于其他网关,因此即使您可以访问网关,也可能无法访问其他网络.这可能是由于例如过滤或缺少到期望网络的路由.

实际上,从这个意义上谈论互联网是没有意义的,因为在任何特定时刻你可能永远无法访问整个互联网.因此,找出您需要能够访问和验证该网络的连接.

我建议这个简单的代码,因为tracert并不总是有效,并且whatsmyip.com不是专门为此目的而设计的:

private void GetIP()
{
    WebClient wc = new WebClient();
    string strIP = wc.DownloadString("http://checkip.dyndns.org");
    strIP = (new Regex(@"\b\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\b")).Match(strIP).Value;
    wc.Dispose();
    return strIP;
}

这是我尝试获取默认IPv4地址而不必诉诸DNS或外部进程调用ipconfig和route等命令.希望.Net的下一个版本将提供对Windows路由表的访问.

public static IPAddress GetDefaultIPv4Address()
{
    var adapters = from adapter in NetworkInterface.GetAllNetworkInterfaces()
                   where adapter.OperationalStatus == OperationalStatus.Up &&
                    adapter.Supports(NetworkInterfaceComponent.IPv4)
                    && adapter.GetIPProperties().GatewayAddresses.Count > 0 &&
                    adapter.GetIPProperties().GatewayAddresses[0].Address.ToString() != "0.0.0.0"
                   select adapter;

     if (adapters.Count() > 1)
     {
          throw new ApplicationException("The default IPv4 address could not be determined as there are two interfaces with gateways.");
     }
     else
     {
         UnicastIPAddressInformationCollection localIPs = adapters.First().GetIPProperties().UnicastAddresses;
         foreach (UnicastIPAddressInformation localIP in localIPs)
         {
            if (localIP.Address.AddressFamily == AddressFamily.InterNetwork &&
                !localIP.Address.ToString().StartsWith(LINK_LOCAL_BLOCK_PREFIX) &&
                !IPAddress.IsLoopback(localIP.Address))
            {
                return localIP.Address;
            }
        }
    }

    return null;
}