dns forwarder 语句的问题

zllian

三个语句放在一起，迷惑了，请高手指点下！

前两个是在named-master-zones.conf 里

zone "corp.ad.aa.com" {
  type forward;
  forwarders { 10.15.1.21; 10.15.1.22; };
  forward only;
};


zone "but.aa.com" {
  type master;
  file "master/db.but";
};


这一个是在named-misc-zones.conf里

zone "google.com"              { type forward; };

看到解释forward，没明白：
forward        A zone of type forward is simply a way to configure forwarding on a per-domain or per zone basis. To be effective both a forward and forwarders statement should be included. If no forwarders statement is present or an empty list is provided then no forwarding will be done for the domain canceling the effects of any forwarders in the options clause.

解释里说，不会把google.com forward出去，那这个zone如何查询？从谁哪里得到返回值，或者结果？

zllian

各位来围观下嘛