DNS

Domain Name System (DNS) is a system for naming computers and network services that is organized into a hierarchy of domains. DNS naming is used in TCP/IP networks, such as the Internet, to locate computers and services through user-friendly names by resolving the name to other information associated with the name, such as an IP address.

A name query begins at a client computer and is passed to a resolver, the DNS Client service, for resolution. If the queried name can be resolved, the query is answered and the process is completed. The local resolver cache can include name information obtained from a Hosts file configured locally Resource records obtained in answered responses from previous DNS queries are added to the cache and kept for a period of time (Time to Live). If the query does not match an entry in the cache, the resolution process continues with the client querying the preferred DNS server to resolve the name. If no preferred DNS servers are available, then alternate DNS servers are used.

The DNS server checks to see if it can answer the query authoritatively based on resource record information contained in a locally configured zone on the server or if no zone information exists for the queried name, using locally cached information from previous queries. Otherwise the DNS server tries to resolve the name with the help of other DNS servers that are authoritative for the root of the DNS domain namespace tree called root hints either directly or through a specific DNS server on the network designated as a forwarder.

A DNS database consists of one or more zone files used by the DNS server which is a collection of structured resource records.

Host address (A) record. Maps a DNS domain name to a single 32-bit IP version 4 address. (RFC 1035)

Alias record. Indicates an alternate or alias DNS domain name for a name already specified in other resource record types used in this zone. The record is also known as the canonical name (CNAME) record type. (RFC 1035)

Host address (AAAA) record for IPv6 hosts. Maps a DNS domain name to a single 128-bit IPv6 address. (RFC 1886)

Mail exchanger (MX) record. Provides message routing to a specified mail exchange host that is acting as a mail exchanger for a specified DNS domain name.

Pointer (PTR) record. Points to a location in the domain name space. PTR records are typically used in special domains to perform reverse lookups of address-to-name mappings. Each record provides simple data that points to some other location in the domain name space (usually a forward lookup zone). Where PTR records are used, no additional section processing is implied or caused by their presence. (RFC 1035)

By default, computers that are statically configured for TCP/IP attempt to dynamically register host (A) and pointer (PTR) resource records (RRs) for IP addresses configured and used by their installed network connections. By default, all computers register records based on their fully qualified domain name (FQDN) which is generated by appending the location of the host in the domain namespace tree called the primary DNS suffix to its host name.

Service Display Name: DNS Client

Registry Key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Dnscache

ServiceDll: %SystemRoot%\System32\dnsrslvr.dll

Resolves and caches Domain Name System (DNS) names for this computer.