What it is
DNS translates domain names into the addresses machines actually use. A domain publishes several record types: A and AAAA for addresses, MX for mail, NS for nameservers, CNAME for aliases, and TXT for arbitrary text.
Why it matters
Address records point at the servers. MX records name the mail provider. TXT records tend to accumulate verification strings from every service the organisation has ever signed up to. Together they sketch out how the domain is run, and who runs parts of it.
Key terms
- A and AAAA Records
- Point a domain to its server's IP address. A records hold IPv4 addresses, and AAAA records hold IPv6 ones.
- CNAME Record
- Makes one domain name an alias for another, often to point a subdomain at a hosting service. If you cancel the service but leave the record, someone else may be able to take over the subdomain.
- MX Records
- List the servers that receive email for the domain, in order of preference.
- SOA Record
- Holds the basic settings for a domain's DNS, such as its main nameserver, an admin email address, and how often other nameservers check for changes.
- PTR Record (Reverse DNS)
- The reverse of an A record, mapping an IP address back to a hostname. Mail servers often reject email from servers without one.
- TTL (Time to Live)
- How long, in seconds, resolvers may keep a DNS answer before asking again. Long TTLs make lookups faster, but changes take longer to reach everyone.