DNS Record Types
Most of the time, when someone talks about a DNS record, they are referring to the simple "directory enquiries" way of mapping a computer's name to its IP address, but this isn't always the case. The DNS can be used to find out other information as well by using different DNS record types.
Common DNS Record Types
- A record
- This translates a computer's name to its IP address.
- PTR record
- This translates a computer's IP address to its name. If set up correctly, the A record and PTR record for any machine on the Internet should match (just lookup one to find the other). In practice, the PTR record is often forgotten, which can cause occasional problems.
- MX record
- This returns the name of the mail server for a domain. This is mainly used by email servers so that they know which machine they should deliver outgoing messages to.
- NS record
- This returns the name of the name server for a domain. It is this that allows one name server to refer you to another when needed (e.g. looking up details in a subdomain)
- TXT record
- The TXT record stores general-purpose text. Originally this was used for descriptions and other helpful information, but nowadays it is also used to store information for specific services (e.g. the SPF email anti-fraud system)
- CNAME record
- A CNAME record provides a way to give an alias to a host name, typically used to give friendly names for computers with hard-to-remember ones.
- SOA record
- This one is a bit special. SOA stands for "start of authority" and it exists in every single Internet domain, providing information used by other name servers to ensure they carry up to date information about the zones they manage.
Just to add an extra level of complexity, most of the above types can have more than one value. For example, an MX record can list multiple mail servers along with a preference value to indicate in which order they should be contacted (try one and if it doesn't answer try the next on the list).
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