做了CDN获取用户真实IP的方法Asp.net

Asp.net获取客户端真实IP,非代理地址
public string GetUserIP()
   {
       string _userIP;
       if(Request.ServerVariables["HTTP_VIA"] == null)
         {
             userIP= Request.UserHostAddress;
         }
       else
        {
           userIP= Request.ServerVariables["HTTP_X_FORWARDED_FOR"];
        }
       return userIP;
    }