DNS Resource Records

There are many types of DNS record types (source). These are all specified in a DNS zone file, which ultimately resolves domain names to ip addresses or other types of records:

• SOA: Start of Authority, mandatory in all zone files, it identifies DNS information about the domain like the name of the DNS server, version, default TTL
• A: Address Record, returns a 32-bit IPv4 address
• AAAA: IPv6 Address Record, returns a 128-bit IPv6 address
• CNAME: Canonical Name Record, aliases one name to another, the DNS lookup will continue by retrying with the new name
• NS: Name Server Record, delegates a DNS zone to use instead of the current DNS zone
• MX: Mail Exchange Record, maps a domain name to a list of message transfer agents for that domain
• TXT: Text Record, plain text, often used to carry data (like a basic api)
• PTR: Reverse DNS record, takes IP address and returns DNS record

TTL (time to live) is another field in the DNS zone file, which specifies how long a caching server should serve the record from its cache rather than from the nameserver again.