获取外网IP

private static string getIP()
{
Uri uri = new Uri(" http://www.ip.cn/getip.php?action=getip&ip_url=");
System.Net.HttpWebRequest req = (System.Net.HttpWebRequest)System.Net.WebRequest.Create(uri);
req.Method = "POST";
req.ContentType = "application/x-www-form-urlencoded";
req.ContentLength = 0;
req.CookieContainer = new System.Net.CookieContainer();
req.GetRequestStream().Write(new byte[0], 0, 0);
System.Net.HttpWebResponse res = (System.Net.HttpWebResponse)(req.GetResponse());
System.IO.StreamReader rs = new System.IO.StreamReader(res.GetResponseStream(), System.Text.Encoding.GetEncoding("GB18030"));
string s = rs.ReadToEnd();
rs.Close();
req.Abort();
res.Close();

int start = s.IndexOf(">");
int end = s.IndexOf("</");
s = s.Substring(start + 1, end - start - 1);

return s;
}