DNS Resource Record Types

There are a number of different types of data, or resource records, that can be stored in DNS for a given domain name. This is a selection of the commonly-used resource record types as given by their symbolic names, as might appear in a DNS zone data file.

A w.x.y.z

An IPv4 address (32 bits/four bytes).

AAAA xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx

An IPv6 address (128 bits/16 bytes).

CNAME a.domain.name.

A Canonical NAME, aliasing another domain name to the indicated target domain name.

MX n a.domain.name.

A Mail EXchanger record. n is a numeric priority; MTAs should use multiple MXes starting with the lowest priority, and select randomly from multiple MXes with the same priority.

TXT stuff

An arbitrary-format text string; essentially a publicly-visible comment about that object.

NS a.name.server.

The indicated host is a Name Server for this domain name.

PTR a.domain.name.

In subzones of the in-addr.arpa. zone, these records are used to associate IPv4 addresses with domain names.

SOA stuff

Start Of Authority record for a DNS zone. This tells a nameserver that it is authoritative for a zone, and contains several subfields controlling the behavior of secondary servers for a zone.

Note that it's common to fully qualify each domain name including a final ".". In particular in zone files this prevents the zone's name from being appended to unqualified names by default. (More on this later when we talk about DNS configuration.)

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