DNS Lookup Client
Applications perform DNS lookups with the aid of a DLL. They call library functions in the DLL, which in turn handle all communications with DNS servers (over UDP or TCP) and return the final results of the lookup back to the applications.
Microsoft's DNS client also has optional support for local caching, in the form of a DNS Client service (also known as DNSCACHE). Before they attempt to directly communicate with DNS servers, the library routines first attempt to make a local IPC connection to the DNS Client service on the machine. If there is one, and if such a connection can be made, they hand the actual work of dealing with the lookup over to the DNS Client service. The DNS Client service itself communicates with DNS servers, and caches the results that it receives.
Microsoft's DNS client is capable of talking to multiple DNS servers. The exact algorithm varies according to the version, and service pack level, of the operating system; but in general all communication is with a preferred DNS server until it fails to answer, whereupon communication switches to one of several alternative DNS servers.
Read more about this topic: Microsoft DNS
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“A client is to me a mere unit, a factor in a problem.”
—Sir Arthur Conan Doyle (1859–1930)