Domain Name Server

Domain Name Servers (DNS) map URL to IP addresses. When a URL is entered in a browser, it is forwarded to a DNS server, directing the request to the correct server.

DNS store details as records, the most common are:

NS (Nameserver)Hold DNS records, permitting DNS lookups within zones. Usually set with the registrar and delegate domain or subdomain to a name server.
A (Address)Map host name to IPv4 address. A blank (@ record) points your main domain to a server. Wildcard are permitted. AAAA (Address) Map host name to IPv6 address.
CNAME (Canonical Name)Alias for the host name, commonly used to link a subdomain to a domain’s A/AAAA record instead of creating two separate records.
MX (Mail Exchange)Permits mail sending to mail servers within the domain. IP addresses or fully qualified domain names.
PTR (Pointer)The opposite of A (Address), maps an IP address to a hostname for reverse lookup. Commonly used as spam verification to confirm a mail server is authorised to use the domain email is coming from.
SOA (Start of Authority)Declares the most authoritative host for the zone and every zone should include an SOA.TXT (Text Record) allow arbitrary text, used for SPF records. SPF records prevent a domain being used by spam. Format is v=spf1 ip4. a -all multiple mail server ID can be given.

To help visualise the sequence of messages: