Re: [討論] 關於 Google DNS 的一些誤區及迷思

看板Google作者SmallBeeWayn (喵喵叫的蜜蜂貓)時間13年前 (2011/04/18 00:52)推噓6(6推 0噓 6→)

留言12則, 5人參與討論串3/4 (看更多)

就像前一位回文者所說，這裡是ROC不是PRC 你的網路路徑上面，不太容易遇到被人劫持跟檢查接著，你跟DNS之間的回應時間影響很大，這取決於中間經過的路由頻寬與壅塞程度還有伺服器的反應時間以 Google 兩台DNS來說不管從Hinet還是Tanet去tracert 都只要不到25ms, 路徑也很短, 與Hinet直連Hinet DNS所差無幾所以可以肯定台灣本島有Google DNS主機, 與Hinet延遲時間相等接著，系統穩定度方面，我相信Hinet很穩，不過我對Google更有信心些再來，就是快取大小與查詢時間... 當你向DNS詢問IP，若DNS自己沒有就會往上轉發，然後存進本機快取並回傳如果快取越大，轉送查詢的機會就越小... 這方面，我相信Google應該是強多了快取大之後，再來就是存活時間了 DNS伺服器不會永遠地留下快取，而是一段時間之後就刪除(因為可能會改IP) 一般來說服務端那邊如果修改Host<=>IP對應，散佈時間號稱24hr以內而Google由於需要經常的到處爬網頁，DNS查詢量很大可能會有額外的檢查機制(例如說如果連不到就要求DNS重問一次) 這對於Google DNS的使用者也是利多就算真的需要DNS幫你轉送好了，由於這個轉送請求是DNS發的(不是自己去要) Google的全球專線網絡其反應速度與安全性絕對不是國內ISP所能企及的 ======= Google DNS標榜的所有效果，前提都是你的電腦<==>Google DNS之間是安全快速的之後的安全，快速，反劫持才是Google DNS能幫妳做到的 ======= 至於Open DNS，主機位在香港，延遲時間就明顯地慢多了 -- ※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 122.116.180.163 ※ 編輯: SmallBeeWayn 來自: 122.116.180.163 (04/18 00:56)

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AlanLive

04/18 07:06, , 1^F

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AlanLive

04/18 07:06, , 2^F

04/18 07:06, 2^F

如果真有這種問題，第一個受害的是Google自己因為它會爬不到東西... 而且，DNS也不是甚麼複雜的技術，錯誤出現在DNS是很不容易的

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knight00931

04/18 11:17, , 3^F

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knight00931

04/18 11:17, , 4^F

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knight00931

04/18 11:17, , 5^F

04/18 11:17, 5^F

http://code.google.com/intl/zh-TW/speed/public-dns/faq.html I've read claims that Google Public DNS can slow down multimedia applications such as iTunes and Apple TV. Are these true? Many sites that provide downloadable or streaming multimedia host their content with DNS-based third-party content distribution networks (CDNs), such as Akamai. When a DNS resolver queries an authoritative nameserver for a CDN's IP address, the nameserver returns an address which is closest (in network distance) to the resolver, not the user. In some cases, for ISP-based resolvers as well as public resolvers such as Google Public DNS, the resolver may not be in close proximity to the users. In such cases, the browsing experience could be slowed down somewhat. Google Public DNS is no different from other DNS providers in this respect. CDN的原理需要知道請求者IP所屬的區域然而當這個發出者不是終端用戶而是DNS時，CDN是根據DNS所處區域來回應的這樣的狀況可能造成瀏覽體驗變慢 To help reduce the distance between DNS servers and users, Google Public DNS has deployed its servers all over the world. In particular, users in Europe should be directed to CDN content servers in Europe, users in Asia should be directed to CDN servers in Asia, and users in the eastern, central and western U.S. should be directed to CDN servers in those respective regions. We have also published this information (see Where are your servers currently located? for details) to help CDNs provide good DNS results for multimedia users. 為了減少DNS與用戶端的距離，Google DNS部屬於世界各地同時Google亦公開了(位置)資訊，以協助CDN提升服務品質

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AlanLive

04/18 12:27, , 6^F

04/18 12:27, 6^F

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AlanLive

04/18 12:27, , 7^F

04/18 12:27, 7^F

大型跨國企業有時候會購買專線頻寬以確保國際通訊的穩定性與速度價錢非常昂貴，幾乎只用於企業內部至於面向客戶端的內容服務，通常還是以CDN為主 ※ 編輯: SmallBeeWayn 來自: 122.116.180.163 (04/18 16:53)

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knight00931

04/18 20:49, , 8^F