C#获得外网的IP地址

static string GetIP()
 2 {

//http://www.ip138.com/ip2city.asp
 3  Uri uri = new Uri("http://www.ikaka.com/ip/index.asp");
 4  System.Net.HttpWebRequest req = (System.Net.HttpWebRequest)System.Net.WebRequest.Create(uri);
 5  req.Method = "POST";
 6  req.ContentType = "application/x-www-form-urlencoded";
 7  req.ContentLength = 0;
 8  req.CookieContainer = new System.Net.CookieContainer();
 9  req.GetRequestStream().Write(new byte [0], 0, 0);
10  System.Net.HttpWebResponse res = (System.Net.HttpWebResponse)(req.GetResponse());
11  StreamReader rs = new StreamReader(res.GetResponseStream(), System.Text.Encoding.GetEncoding("GB18030"));
12  string s = rs.ReadToEnd();
13  rs.Close();
14  req.Abort();
15  res.Close();
16  System.Text.RegularExpressions.Match m = System.Text.RegularExpressions.Regex.Match(s, @"IP：\[(?<IP>[0-9\.]*)\]");
17  if (m.Success) return m.Groups["IP"].Value;
18  return string.Empty;
19 }