[译]管理Windows 2000 Pro中的DNS客户端缓存

http://techrepublic.com.com/5100-10877_11-6029680.html?tag=nl.e116

Manage the DNS client cache in Windows 2000 Pro
管理Windows 2000 Pro中的DNS客户端缓存

by Jim Boyce
作者：purple endurer
Keywords: Windows 2000 | Microsoft Windows | Domain names
关键字：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：
如果对一个主机的查询因为负责其域名解析的DNS服务器关闭而失败，那么后续的查询该主机的尝试也将因为（先前的）失败结果被缓存而不成功。让我们学习克服这个问题的两种方法。

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这样的完全合法的主机名被解析为目标IP地址。您每次访问一个网站，Windows 2000 Professional内置的DNS客户端软件执行一次指特主机名的查询以获得目标服务器的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客户端缓存查询的每一个名字，用以加速后续的地址请求。默认缓存时限为30分钟。如果一个查询结果长于30分钟，Windows执行一个主机扩展查询并刷新缓存拷贝。

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.
尽管缓存能改善名字解析性能，但它也能负面影响解析。除了缓存有效结果之外，Windows也缓存不良结果。所以，如果对一个主机的查询因为负责其域名解析的DNS服务器关闭而失败，那么后续的查询该主机的尝试也将因为（先前的）失败结果被缓存而不成功。您可以用下列两种方法之一克服这个问题：刷新DNS缓存并在服务器重新上线时重试，或者修改缓存时限。

To change cache timeout, open the Registry Editor and add the DWORD value
要修改缓存时限，打开注册表编辑器并增加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，以秒为单位设置DnsCacheTimeout值。

To flush the DNS cache altogether, use the following command at a console prompt:
要刷新DNS缓存，在命令控制台使用下列命令：

ipconfig /flushdns

Note: Editing the registry is risky, so be sure you have a verified backup before saving any changes.