Overview of DNS
Domain name translation is fundamental to Internet usage. The Internet recognizes domains as IP addresses; however, Internet users prefer to use names, rather than IP addresses, to identify domains. Consequently, the domain names that users specify must be translated into IP addresses for use by the Internet. The Domain Name System (DNS) is the mechanism that makes this translation.
DNS is a distributed database that performs name translations. To manage this information effectively DNS has a distributed architecture composed of many DNS servers in a hierarchical fashion. Each server is responsible for both name-to-IP-address (forward) and IP-address-to-name (reverse) translations (called lookups).
The DNS system is, in fact, its own network. The important point is that it is a distributed network. Thus, no single server or organization has or owns the DNS information of the Internet. If one DNS server does not know how to translate a particular domain name, it asks another one, and so on, until the correct IP address is returned.
Each DNS server manages the lookups for one or more domain name spaces, called zones.
Each DNS server also maintains a list of all domain names and their associated IP addresses. The elements on this list are known as records. Once you have created a zone, you add records to that zone. A zone can contain the following types of records:
Host record: An IP address for forward or host name-to-IP address mapping.
Alias (CNAME) record: A mapping between one host name and another. This record tells the DNS server that any requests made to the alias name are to be redirected to the host to which the alias points. The target host does not have to be within the local domain.
Mail Exchanger (MX) record: Specifies a mail exchanger for the domain. The mail exchanger is a host that either processes or forwards email for the domain.
Name Server (NS) record: The host name of a DNS server that is authoritative for the domain. A DNS zone requires at least one NS record. If there is only one NS record in a zone, it cannot be removed.
Pointer (PTR) record: A host name for reverse (IP address-to-host name) mapping.
Each DNS zone has a Start of Authority (SOA) record. When you add a zone to a domain, a SOA record is automatically created.
The SOA record:
Designates the start of the zone and specifies where in the domain name space the name server has authority.
Specifies timing information for zone transfers, which are the transfers of lookup data from the primary name server to the secondary server.
Provides contact information for a zone. Every zone’s SOA record contains the email address of the zone’s technical contact.