多网卡的环境下的发包

//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();