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迭代一词应是翻译自“Iteration”。
目前我没有发现RFC上有关于Iteration的说法。这一词应该出自于《DNS and Bind》5th edition这本书。见这本书的第2.6.2节 Recursion部分与2.6.3节Iteration部分。- Queries come in two flavors, recursive and iterative, also called nonrecursive. Recursive queries place most of the burden of resolution on a single nameserver. Recursion, or recursive resolution, is just a name for the resolution process used by a nameserver when it receives recursive queries. As with recursive algorithms in programming, the nameserver repeats the same basic process (querying a remote nameserver and following any referrals) until it receives an answer.
- Iteration, or iterative resolution, on the other hand, refers to the resolution process used by a nameserver when it receives iterative queries.
复制代码- Iterative resolution doesn't require nearly as much work on the part of the queried nameserver. In iterative resolution, a nameserver simply gives the best answer it already knows back to the querier. No additional querying is required. The queried nameserver consults its local data (including its cache, which we'll talk about shortly), looking for the data requested. If it doesn't find the answer there, it finds the names and addresses of the nameservers closest to the domain name in the query in its local data and returns that as a referral to help the querier continue the resolution process. Note that the referral includes all nameservers listed in the local data; it's up to the querier to choose which one to query next.
复制代码 从上面的文字可以看出,迭代(Iteration)即为递归查询Non-recursive的意思,就是DNS查询包中没有设置RD(Recursion Desired)位。 |
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