public static String fromInAddrArpa(String arpa){
		String[] ipn = arpa.split("\\.");
		if(ipn.length==6 && ipn[4].equalsIgnoreCase("in-addr") && ipn[5].equalsIgnoreCase("arpa"))
			return ipn[3]+"."+ipn[2]+"."+ipn[1]+"."+ipn[0];
		return null;
    }