DNS解析顺序和递归非递归查询

顺序为：

本地DNS缓存

本地HOSTS文件

DNS服务器

在RFC1034 4.3.1中有这样的描述：
•The simplest mode for the server isnon-recursive, since it can answer queries usingonly local information:
the response contains an error, the answer, or a referral to some other server"closer" to the answer.
All name servers must implement non-recursive queries.
•The simplest mode for the client is recursive, since in this mode the name server acts inthe role of a resolver
and returns either an error or the answer, but never referrals. This service isoptional in a name server, and
the name server may also choose to restrict the clients which can use recursivemode.b