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DNS Resolver Cache Service

Windows 2000 includes a caching DNS resolver service, which is enabled by default. For troubleshooting purposes this service can be viewed, stopped, and started like any other Windows 2000 service. The caching resolver reduces DNS network traffic and speeds name resolution by providing a local cache for DNS queries.

Name query responses are cached for the TTL specified in the response (not to exceed the value specified in the MaxCacheEntryTtlLimit registry entry (HKLM\SYSTEM\CurrentControlSet\Services\Dnscache\Parameters)), and future queries are answered from cache when possible. DNS Resolver Cache Service supports negative caching. For example, if a query is made to a DNS for a particular host name and the response is negative, succeeding queries for the same name will be answered (negatively) from the cache for an amount of time equal to the value in the NegativeCacheTime registry entry (HKLM\SYSTEM\CurrentControlSet\Services\Dnscache\Parameters) (the default value is 300 seconds). Another example of negative caching is that if all DNS servers are queried and none are available, for an amount of time equal to the value in the NetFailureCacheTime registry entry (HKLM\SYSTEM\CurrentControlSet\Services\Dnscache\Parameters) (the default value is 30 seconds), all succeeding name queries fail instantly instead of timing out. This feature saves time for services that query the DNS during the boot process, especially when the client is booted from the network.

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