http://techrepublic.com.com/5100-10877_11-6029680.Html?tag=nl.e116Manage the DNS client cache in windows 2000 PRo 治理Windows 2000 Pro中的DNS客戶端緩存by Jim Boyce 作者：purple endurer KeyWords: Windows 2000 Microsoft Windows Domain names 要害字：Windows 2000 Microsoft Windows 域名 Takeaway: If a lookup fails for a host because the target domain's DNS server is down, then subsequent attempts to look up the host will also fail because the failed results are cached. Learn two ways to overcome this problem. 概述： 假如對一個主機的查詢因為負責其域名解析的DNS服務器關閉而失敗，那么后續的查詢該主機的嘗試也將因為（先前的）失敗結果被緩存而不成功。讓我們學習克服這個問題的兩種方法。 DNS enables fully qualified host names like www.techrepublic.com to be resolved to their target ip addresses. Every time you visit a Web site, the DNS client software built into Windows 2000 Professional performs a DNS lookup of the specified host name to oBTain the IP address of the target server. DNS能使www.techrepublic.com這樣的完全合法的主機名被解析為目標IP地址。您每次訪問一個網站，Windows 2000 Professional內置的DNS客戶端軟件執行一次指特主機名的查詢以獲得目標服務器的IP地址。The DNS client caches the results of each name lookup to speed up subsequent requests for the address. The default cache timeout is 30 minutes. If a lookup result is longer than 30 minutes, Windows performs an external lookup of the host and refreshes the cached copy. DNS客戶端緩存查詢的每一個名字，用以加速后續的地址請求。默認緩存時限為30分鐘。假如一個查詢結果長于30分鐘，Windows執行一個主機擴展查詢并刷新緩存拷貝。Although caching can improve name resolution performance, it can also affect resolution in a negative way. In addition to caching positive results, Windows also caches negative results. So, if a lookup fails for a host because the target domain's DNS server is down, then subsequent attempts to look up the host will also fail because the failed results are cached. You can overcome this problem in one of two ways: flush the DNS cache and try again when the server comes back on line, or change the cache timeout. 盡管緩存能改善名字解析性能，但它也能負面影響解析。除了緩存有效結果之外，Windows也緩存不良結果。所以，假如對一個主機的查詢因為負責其域名解析的DNS服務器關閉而失敗，那么后續的查詢該主機的嘗試也將因為（先前的）失敗結果被緩存而不成功。您可以用下列兩種方法之一克服這個問題：刷新DNS緩存并在服務器重新上線時重試，或者修改緩存時限。To change cache timeout, open the Registry Editor and add the DWORD value 要修改緩存時限，打開注冊表編輯器并增加DWORD型值： HKEY_CURRENT_USER/Software/Microsoft/Windows/CurrentVersion/Internet Settings/DnsCacheTimeout. Set the value of DnsCacheTimeout to the number of seconds you want entries to be cached. 按你所想，以秒為單位設置DnsCacheTimeout值。To flush the DNS cache altogether, use the following command at a console prompt: 要刷新DNS緩存，在命令控制臺使用下列命令：ipconfig /flushdnsNote: Editing the registry is risky, so be sure you have a verified backup before saving any changes.
