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== DNS/recursion ==

http://www.tech-faq.com/understanding-dns-queries-and-lookups.html

{{{
If a DNS server cannot find the queried name in its zone information, or in its cache; 
  the DNS server performs recursion to resolve the name. 
This is the default configuration for DNS servers.
Recursion is the process whereby which the DNS server queries other DNS servers for the client.
}}}

Referral answer: 
   A referral response is returned if the DNS server does not support recursion.
A referral contains additional resource records for resolving the request.

== コンテンツサーバでは再帰検索させてはいけない ==
キャッシュサーバには「毒を盛られる」危険が常に存在します。

http://internet.watch.impress.co.jp/cda/news/2005/10/26/9625.html

自ドメインのデータを公開するのがコンテンツサーバです。
コンテンツサーバは通常は全世界に公開されます。

検索を代行するのはキャッシュサーバです。
こちらはアクセス制限して、第三者には使われないようにしましょう。