April 2015
Intermediate to advanced
372 pages
6h 56m
Chinese
Content preview from SDN: 軟體定義網路
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虛擬化多租戶資料中心 | 177
• 安全的網路環境。
• 拓撲結構不會輕易改變。
• 專責的管理人員。
• 傳輸成本為零。
• 網路環境是同質性的（Homogeneous）。
一開始這些假設概念看起來似乎很有道理，但是在實際環境中卻很難（或不可能）達
成。例如，前面四點對於採用的技術，和希望達成這些技術的設備進行假設。但是，
並沒有哪一家的設備是完美或不會出錯的，所以事實上我們做出相反的假設可能更為
安全。第四點到第六點牽涉管理或人為因素，因為一旦網路環境配置好了，就應該一直
這樣運作下去直到需要修改。但是也暗藏一些問題：從網路的正常運作角度來看，配置
錯誤（例如，輸入錯誤）可能是災難性，還可能無意中引發安全性漏洞。（統計資料顯
示，在節日 / 假日期間，網路管理人員沒有進行任何操作時，網路出錯機率反而是下降
的 。）
資料中心分散式運算的陷阱
DCI 必須要考慮到租戶的位址空間有可能重疊，例如，使用 L2 MPLS VPN、L3 MPLS
VPN、GRE Tunnels、SSL VPN 或其他隧道機制分隔位址空間。根據所選擇不同的位址
管理原則時，這可能會導致出現前面 6.3.5 節中所討論過的問題。特別是，位址重疊又
需要隔離保護的時候，如果配置失誤使某位租戶不小心能夠看到其他租戶的 VM 虛擬主
機，就會出大問題。所以請記住，位址管理方案的選擇並不是那麼簡單，需要考慮操作
因素、管理驗證和檢查機制。
資料中心互相連結也是有效能上的評估標準。許多限制來自於資料中心（之前討論過，
包括磁碟 I/O
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I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.