Fedora Linux

the time in seconds; some examples are shown in Table 7-5.

Table 7-5. named time values

Entry	Description	Equivalent number of seconds
3D	3 days	259,200
1D12H 36H	1 day and 12 hours (or 36 hours)	129,600
2W	2 weeks	1,209,600
1D10M	1 day and 10 minutes	87,000

The zone file then contains the Start of Authority (SOA) resource record:

@ SOA ns1 chris.global.proximity.on.ca. (2007201702,3D,1H,3D,1H)

The @ sign means 'this zone', and SOA is the record type. The values are the authoritative master nameserver ( ns1 ), followed by the administrative email contact, with the @ converted to a period (therefore, usernames containing periods cannot be used for administrative contacts).

All hostnames and domain names in a zone file will have the name of the zone added to the end of them unless they end with a period. Thus, in this example, bluesky (with no period) would be interpreted as bluesky.fedorabook.com, as would bluesky.fedorabook.com with no period: bluesky.fedorabook.com.fedorabook.com. 

The values in parentheses at the end of the record are the serial number and the time values for this record. It's helpful (and common practice) to split this information across several lines and add comments to label which time value is which:

@ SOA ns1 chris.global.proximity.on.ca. (
 2007201702 ; serial number
 3D ; refresh
 1H ; retry
 3D ; expire
 1H ) ; minimum

Notice that comments start with a semicolon. The time values used here are the same ones configured using the graphical tool.

The rest of the zone file contains resource records. We need NS records to indicate the nameservers for this domain:

IN NS bluesky
IN NS darkday

The first field is blank; the line must be indented at least one space. The next field value, IN , specifies that these records are related to the Internet (TCP/IP address family). NS indicates the record type (nameserver), and the last field is the hostname of the nameserver.

We also need A records to indicate the IP address of each computer:

bluesky IN A 216.183.93.224
darkday IN A 216.183.93.225

The first field in each record is the hostname, followed by the address family ( IN ) and the record type ( A ), and then the IP address.

Next we have MX records for mail exchangers:

IN MX 10 bluesky
IN MX 20 global.proximity.on.ca.

These have a blank first field, followed by the address family ( IN ) and record type ( MX ), followed by the mail server priority (lower numbers are higher priority), and then the mail server hostname.

Note that global.proximity.on.ca is outside of this zone, so the hostname is written as a fully qualified domain name (FQDN) ending with a period.

We also need some aliases for common hostnames:

mail IN CNAME bluesky
ftp IN CNAME darkday
www IN CNAME bluesky
ww IN CNAME bluesky
wwww IN CNAME bluesky

These records are like A records, except that the record type is set to CNAME and the last field contains the canonical (true) hostname.

It is possible to override the default TTL by inserting it between the address family ( IN ) and the record type in each record. For example, you could set the TTL for the last CNAME record to five minutes:

wwww IN 5M CNAME bluesky

Putting this all together and adding some comments gives us the complete zone file:

; Zone file for 'fedorabook.com'
; Default TTL is 1 hour
$TTL 1H
; Start of authority
@ SOA ns1 chris.global.proximity.on.ca. (