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This document lists the basic usage of commonly used DNS records. It can be used to track commonly made mistakes.

A

Points to an IPv4 address.
Does not point to anyhting else.
Record does not start (left side) with _ or -.

AAAA

Points to an IPv6 address.
Does not point to anyhting else.
Record does not start (left side) with _ or -.

MX

Points to an A and/or AAAA record.
Preferrably does not point to other record types, but the use of CNAME records is seen in practice. RFC's are inconsistent on this.
Has a priority value.

CNAME

Points to other records (A, AAAA, CNAME).
Be carefull with CNAME chaining; don't use too many CNAMEs in a row.
The end of a CNAME chain is always an A an/or AAAA record.
Can only be combined with NS / SOA records if left side is equal.

SRV

Records starts (left side) with _.
Points to an A and/or AAAA record.
Has a priority value.

NS

Points to an A and/or AAAA record.
Used to point to subzones.
Used to indicate what is inside the parent zone.
Each zone needs this to indicate what is inside the parent zone as a reference to this zone.

SOA

Mandatory for every DNS zone.
Contains the following information (seperated by a single white space):
- FQDN of the primairy name server followed by a trailing dot.
- e-mail address of the DNS administrator (followed by a trailing dot, the @ replaced with a dot).
- an opening round bracket "(".
- serial number that is changed (increased) on every zone change.
- refresh time (in seconds) for a secondary name server to check the primairy name server for changes in the zone.
- retry time (in seconds) for a secondary name server for requesting the serial number when the primary name server did not respond on the previous request.
- expire time (in seconds) after which a secondary name server should stop answering requests if the primary name server is not responding.
- Negative caching time to live (in seconds) which is the time a caching name server should cache a negative result (indicating that a name does not exist) coming from the authorative name server before trying again.
- a closing round bracket ")".