c# proxy arkasındaki ip

public static string GetUserIP() {  

    var ip = ( HttpContext.Current.Request.ServerVariables["HTTP_X_FORWARDED_FOR"] != null

              && HttpContext.Current.Request.ServerVariables["HTTP_X_FORWARDED_FOR"] != "" )

             ? HttpContext.Current.Request.ServerVariables["HTTP_X_FORWARDED_FOR"]

             : HttpContext.Current.Request.ServerVariables["REMOTE_ADDR"];

    if (ip.Contains( "," ))

        ip = ip.Split( ',' ).First().Trim();

    return ip;

}