Ottenere l'IP reale anche con un proxy

RealIP = Request.ServerVariables["REMOTE_ADDR"].ToString();
ClientIP = Request.ServerVariables["HTTP_CLIENT-IP"];

if(ClientIP!="")
{
    RealIP = ClientIP;
}
else
{
    Forwarded = Request.ServerVariables["HTTP_X_Forwarded-For"];
}

if (Forwarded != "")
    RealIP = Forwaded;