Computer Networks · 免费预览
域名系统
路由器需要地址，人类则需要名称，因此互联网运行着一种中间件来完成翻译。这是一个层次化的命名空间，每一层都把权限委托给各个区域——每个区域是由两台或更多名称服务器伺服的管理子树，这些服务器持有多种类型的资源记录：地址记录、用于委托的名称服务器记录、别名、邮件交换器，每条记录都带有生存时间（TTL），这使得缓存成为合法行为。解析时从根出发，沿层次结构向下经过顶级域到达权威服务器；本地递归解析器代表客户端完成这一遍历，并缓存每个应答，因此根服务器只看到全球好奇心的涓涓细流。
1. Names for Humans, Addresses for Routers
Names for Humans, Addresses for Routers
2. From One File to a Hierarchy
From One File to a Hierarchy
3. Records, Types, and the License to Cache
Records, Types, and the License to Cache
4. The Walk Down the Tree
The Walk Down the Tree
5. Middleware's job
Why is a name service called middleware?
6. The unit of delegation
In the DNS hierarchy, what exactly is a zone, and what role does it play in delegation?
7. Reading a record
Which resource record type expresses delegation to a child zone?
8. The load-bearing cache
Why is caching load-bearing in DNS rather than merely an optimization?
9. Recursive versus iterative
Who does the walking when your laptop resolves a name?
10. The second lookup
Two users of the same resolver look up the same popular site in succession. Why is the second lookup fast?
11. The delegation record
Which resource record type names the authoritative server for a child zone?
12. The expiry field
Which resource record field bounds how long an answer may be cached?
13. The walking server
What kind of name server chases referrals from the root down to the authoritative server on a client's behalf?
14. The address answer
Which record type maps a host name to its IP address?