DNS, acronym of Domain Name System. It is a hierarchical client / server distributed database management system that translates the domain name / host into an IP address.
The root of the domain is represented by the tree top or by the .com, .edu, .org, .net
When you type a URL in the appropriate field of the broswer, the computer will contact the DNS servers to determine the address assigned to the requested site. A hostname is a name assigned to a computer within a domain or subdomain identified by an IP address. Multiple hostnames can be assigned an IP address, but only one name can be assigned to a computer. A fully qualified domain name (FQDN) describes the exact location of a host in the DNS hierarchy. Within the DNS zone, there are records (RR) that provide name resolution:
- SOA (Start of Authority): identifies the name server which is the authoritative source of information for a domain or dns zone
- TPR: Resolves an IP address to a hostname
- A (host address): provides a hostname to an IPV4 address
- AAA (host address): provides a hostname to an IPV6 address
- SRV (service): locates hosted servers to particular services, such as domain servers or LDAP servers
- CNAME (canonical name): Creates an alias or alternate DNS domain name for a specific hostname.
- NS (name server): provides a list of server names assigned to the domain
- MX (mail exchanger): identify which email should contact a specific domain
When defining a DNS zone, the zone is created as a direct search zone or reverse lookup zone. The direct search zone has most of the record resources, including records A and CNAME, while the inverse zone has PTR records.
DNS servers use round-robin to distribute and share the load through network resources. Round-robin rotates the order of resource records with the same name on different IP addresses. In Windows Server, with the Active Directory integrating zones, each server provides a primary peer server. This can be done by upgrading any server running integrated zones in the Active Directory and the changes will be replicated to the other DNS servers.
DNS requests are made on port 53.
Books to understand how Windows servers work: