//设置对外访问所使用网卡的IP

string sendingIp = "192.168.0.1";

//设置对外访问所使用的端口

int sendingPort = 5000;

Uri uri = new Uri("http://google.com");

HttpWebRequest wr = (HttpWebRequest)WebRequest.Create(uri);

//获取对外访问的包，并指定使用那个IP（网卡）与端口来发送数据包

ServicePoint sp = ServicePointManager.FindServicePoint(uri);

sp.BindIPEndPointDelegate =

    (servicePoint,remoteEp,retryCount) =>

         {

             return new IPEndPoint(IPAddress.Parse(sendingIp),sendingPort);

         };

//提交请求并获取返回结果

var data = new StreamReader(wr.GetResponse().GetResponseStream()).ReadToEnd();

//获取多网卡Ip
NetworkInterface[] NetworkInterfaces = NetworkInterface.GetAllNetworkInterfaces();
            foreach (NetworkInterface NetworkIntf in NetworkInterfaces)
            {
                IPInterfaceProperties IPInterfaceProperties = NetworkIntf.GetIPProperties();
                UnicastIPAddressInformationCollection UnicastIPAddressInformationCollection = IPInterfaceProperties.UnicastAddresses;
                foreach (UnicastIPAddressInformation UnicastIPAddressInformation in UnicastIPAddressInformationCollection)
                {
                    if (UnicastIPAddressInformation.Address.AddressFamily == AddressFamily.InterNetwork)
                    {
                        MessageBox.Show(UnicastIPAddressInformation.Address.ToString());
                    }
                }
            }