在ASP.NET上如何取得真實的IP？

在ASP.NET上，通常會使用
Request.ServerVariables["REMOTE_ADDR"];
來取得用戶端的IP。

但是有可能會遇到一個問題，當用戶端是透過代理伺服器連入時，則IP會變成是代理伺服器的，而並非是真正的用戶端IP。所以，我們必須使用另外的方式取得用戶端的IP
Request.ServerVariables["HTTP_X_FORWARDED_FOR"];

完整的程式碼如下：

/// <summary>
/// 取得客戶端真實IP Address
/// </summary>
/// <returns></returns>
protected string GetClientIP()
{
    string ip = null;
    if (Request.ServerVariables["HTTP_X_FORWARDED_FOR"].ToString()==string.Empty || Request.ServerVariables["HTTP_X_FORWARDED_FOR"].ToUpper().IndexOf("UNKNOWN") > 0)
    {
        ip = Request.ServerVariables["REMOTE_ADDR"];
    }
    else if (Request.ServerVariables["HTTP_X_FORWARDED_FOR"].IndexOf(",") > 0)
    {
        ip = Request.ServerVariables["HTTP_X_FORWARDED_FOR"].Substring(1, Request.ServerVariables["HTTP_X_FORWARDED_FOR"].IndexOf(",") - 1);
    }
    else if (Request.ServerVariables["HTTP_X_FORWARDED_FOR"].IndexOf(";") > 0)
    {
        ip = Request.ServerVariables["HTTP_X_FORWARDED_FOR"].Substring(1, Request.ServerVariables["HTTP_X_FORWARDED_FOR"].IndexOf(";") - 1);
    }
    else
    {
        ip = Request.ServerVariables["HTTP_X_FORWARDED_FOR"];
    }

    return ip.Replace(' ', string.Empty);
}