Updated: January 21, 2005
Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2
The Domain Name System (DNS) Client service is used to resolve DNS domain names and implements the following features:
Resource records (RRs) from query responses are added to the client cache as applications query DNS servers. This information is then cached for a set Time to Live (TTL) and can be used again to answer subsequent queries.
RFC-compliant negative caching support
In addition to caching positive query responses from DNS servers (which contain resource record information in the answered reply), the DNS Client service also caches negative query responses. A negative response results when a resource record for the queried name does not exist.
Negative caching prevents the repeating of additional queries for names that do not exist, which can adversely affect client system performance. Any query information negatively cached is kept for a shorter period of time than is used for positive query responses; by default, no more than 5 minutes. This avoids continued negative caching of stale information if the records later become available.
Negative caching is a new DNS standard specification defined in RFC 2308. For more information, refer to this RFC. For more information on obtaining RFCs, see TCP/IP RFCs.
Avoidance of unresponsive DNS servers
The DNS Client service uses a server search list, ordered by preference. This list includes all preferred and alternate DNS servers configured for each of the active network connections on the system.
The list is arranged based on the following criteria:
Preferred DNS servers are given first priority.
If no preferred DNS servers are available, then alternate DNS servers are used.
Unresponsive servers are removed temporarily from these lists.
- Preferred DNS servers are given first priority.