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 ip4.11.22.33.44 a -all multiple mail server ID can be given. |
To help visualise the sequence of messages:
