得到外网IP

using System.net;

public void GetIP()
{
WebClient client = new WebClient();
byte[] bytRecv = client.DownloadData("http://www.123cha.com/"); //下载网页数据
string str = System.Text.Encoding.GetEncoding("gb2312").GetString(bytRecv);
//string r = @"(((/d{1,3}) ¦(1/d{2}) ¦(2[0-4]/d) ¦(25[0-5]))/.){3}((/d{1,3}) ¦(1/d{2}) ¦(2[0-4]/d) ¦(25[0-5]))";
string r = @"(((/d{1,3})|(1/d{2})|(2[0-4]/d)|(25[0-5]))/.){3}((/d{1,3})|(1/d{2})|(2[0-4]/d)|(25[0-5]))";
string ip = System.Text.RegularExpressions.Regex.Match(str, r).ToString(); //提取信息

this.TextBox1.Text = IPAddress.Parse(ip).ToString();
}