An example master zone file for example.org (existing within
/etc/namedb/master/example.org) is as follows:
$TTL 3600 ; 1 hour
example.org. IN SOA ns1.example.org. admin.example.org. (
2006051501 ; Serial
10800 ; Refresh
3600 ; Retry
604800 ; Expire
86400 ; Minimum TTL
)
; DNS Servers
IN NS ns1.example.org.
IN NS ns2.example.org.
; MX Records
IN MX 10 mx.example.org.
IN MX 20 mail.example.org.
IN A 192.168.1.1
; Machine Names
localhost IN A 127.0.0.1
ns1 IN A 192.168.1.2
ns2 IN A 192.168.1.3
mx IN A 192.168.1.4
mail IN A 192.168.1.5
; Aliases
www IN CNAME @
Note that every hostname ending in a “.” is an exact hostname, whereas
everything without a trailing “.” is referenced to the origin. For example,
www is translated into www.origin. In our fictitious zone file, our origin is
example.org., so www would translate to
www.example.org.
The format of a zone file follows:
recordname IN recordtype value
The most commonly used DNS records:
- SOA
-
start of zone authority
- NS
-
an authoritative name server
- A
-
a host address
- CNAME
-
the canonical name for an alias
- MX
-
mail exchanger
- PTR
-
a domain name pointer (used in reverse DNS)
example.org. IN SOA ns1.example.org. admin.example.org. (
2006051501 ; Serial
10800 ; Refresh after 3 hours
3600 ; Retry after 1 hour
604800 ; Expire after 1 week
86400 ) ; Minimum TTL of 1 day
- example.org.
-
the domain name, also the origin for this zone file.
- ns1.example.org.
-
the primary/authoritative name server for this zone.
- admin.example.org.
-
the responsible person for this zone, email address with “@” replaced.
(<admin@example.org> becomes admin.example.org)
- 2006051501
-
the serial number of the file. This must be incremented each time the zone file is
modified. Nowadays, many admins prefer a yyyymmddrr format for
the serial number. 2006051501 would mean last modified
05/15/2006, the latter 01 being the first time the zone file has
been modified this day. The serial number is important as it alerts slave name servers
for a zone when it is updated.
IN NS ns1.example.org.
This is an NS entry. Every name server that is going to reply authoritatively for the
zone must have one of these entries.
localhost IN A 127.0.0.1
ns1 IN A 192.168.1.2
ns2 IN A 192.168.1.3
mx IN A 192.168.1.4
mail IN A 192.168.1.5
The A record indicates machine names. As seen above, ns1.example.org would resolve to 192.168.1.2.
IN A 192.168.1.1
This line assigns IP address 192.168.1.1 to the current
origin, in this case example.org.
www IN CNAME @
The canonical name record is usually used for giving aliases to a machine. In the
example, www is aliased to the “master” machine which
name equals to domain name example.org (192.168.1.1). CNAMEs can be used to provide alias hostnames, or round
robin one hostname among multiple machines.
IN MX 10 mail.example.org.
The MX record indicates which mail servers are responsible for handling incoming mail
for the zone. mail.example.org is the hostname of the mail
server, and 10 being the priority of that mail server.
One can have several mail servers, with priorities of 10, 20 and so on. A mail server
attempting to deliver to example.org would first try the highest
priority MX (the record with the lowest priority number), then the second highest, etc,
until the mail can be properly delivered.
For in-addr.arpa zone files (reverse DNS), the same format is used, except with PTR
entries instead of A or CNAME.
$TTL 3600
1.168.192.in-addr.arpa. IN SOA ns1.example.org. admin.example.org. (
2006051501 ; Serial
10800 ; Refresh
3600 ; Retry
604800 ; Expire
3600 ) ; Minimum
IN NS ns1.example.org.
IN NS ns2.example.org.
1 IN PTR example.org.
2 IN PTR ns1.example.org.
3 IN PTR ns2.example.org.
4 IN PTR mx.example.org.
5 IN PTR mail.example.org.
This file gives the proper IP address to hostname mappings of our above fictitious
domain.
