DNS concept

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DNS是什麼

Domain name system （或domain name service）位於OSI七層模型的應用層，領域名稱系統是一種分散式網路系統，用於域名解析，將人容易閱讀的域名轉為電腦可以理解的IP 位址。


運行流程

在瀏覽器輸入www.google.com後前往，首先會檢查本地DNS 緩存，是否有域名為www.google.com對應的IP 位址，若沒有則到本地DNS server （一般為ISP提供）查詢，還是查無就到根DNS server 查詢。會先找.com域名伺服器的IP 位址，接著到.com域名伺服器查詢google.com域名伺服器的IP 位址，再到google.com域名伺服器查詢www.google.com的IP 位址。找到IP 位址就回傳給瀏覽器，瀏覽器就能用IP 位址連到網頁伺服器取得網頁資料。

DNS 運行流程

圖、DNS 運行流程

DNS 觀念應用

觀念可以應用在整理，東西從最近的地方桌子開始找，再找櫃子，如果是經常使用的東西，可以放在最近的桌子，下次要使用，就不用再到櫃子找。

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