Domain Name System (DNS) provides a method of resolving host names to IP addresses on the Internet.
DNS servers host data in zones. You can think of a zone as a database with multiple records. Some common records in a DNS zone are:
- A record (also called a host record). This record holds the host name and IPv4 address assigned to the host. A DNS client queries DNS with the name using a forward lookup request, and DNS responds with the IPv4 address from this record.
- AAAA record. This record holds the host name and IPv6 address. It’s similar to an A record except that it is for IPv6.
- PTR record (also called a pointer record). The PTR record is the opposite of an A record. Instead of a DNS client querying DNS with the name, the DNS client queries DNS with the IP address. When configured to do so, the DNS server responds with the name. PTR records are optional, so these reverse lookups do not always work.
- MX record (also called mail exchanger). An MX record identifies a mail server used for email. The MX record is linked to the A record or AAAA record of a mail server.
- CNAME record (also called a canonical name, or alias). The CNAME record allows a single system to have multiple names associated with a single IP address. For example, a server named Server1 in the domain getcertifiedgetahead.com might have an alias of FileServer1 in the same domain.
- SOA record (also known as the start of authority record). The SOA record includes information about the DNS zone and some of its settings. For example, it includes the TTL (Time to Live) settings for DNS records. DNS clients use the TTL setting to determine how long to cache DNS results. TTL times are in seconds and lower times cause clients to renew the records more often.