The TCP/IP Guide - DNS Master File Format

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Table 179 shows the specific formats and examples for each of the common resource record types. The fields are basically the same as the ones explained in the DNS binary record formats. I have included explanatory “comments” using the DNS comment format. Assume that the examples in this table are for the zone “googleplex.edu”:

**Table 179: DNS Master File Format Syntax and Examples**
Resource Record Text Code	Resource Record Type	Resource Record Format / Example
A	Address	<domain-name> [<ttl>] IN A <ip-address> admin1.googleplex.edu IN A 204.13.100.3 ; A FQDN. admin2 IN A 204.13.100.44 ; A PQDN equivalent to ; admin2.googleplex.edu
NS	Name Server	<domain-name> [<ttl>] IN NS <name-server-name> googleplex.edu. IN NS custns.bigisp.net ; Secondary NS
*CNAME*	Canonical Name	<domain-name> [<ttl>] IN CNAME <canonical-name> www IN CNAME bigserver ; www.googleplex.edu is really ; bigserver.googleplex.edu.
*SOA*	Start Of Authority	<domain-name> [<ttl>] IN SOA <m-name> <r-name> ( <serial-number> <refresh-interval> <retry-interval> <expire-interval> <default-ttl>) googleplex.edu. IN SOA ns1.googleplex.edu it.googleplex.edu ( 42 ; Version 42 of the zone. 21600 ; Refresh every 6 hours. 3600 ; Retry every hour. 604800 ; Expire after one week. 86400) ; Negative Cache TTL is one day.
*PTR*	Pointer	<reverse-domain-name> [<ttl>] IN PTR <domain-name> 3.100.13.204.IN-ADDR.ARPA. IN PTR admin1.googleplex.edu.
MX	Mail Exchange	<domain-name> [<ttl>] IN MX <preference-value> <exchange-name> googleplex.edu. IN MX 10 mainmail.googleplex.edu. IN MX 20 backupmail.googleplex.edu
*TXT*	Text	<domain-name> [<ttl>] IN TXT <text-information> googleplex.edu. IN TXT "Contact Joe at X321 for more info."

Note that the PTR record would actually be in the IN-ADDR.ARPA domain, of course.

Table 180 contains a “real-world” example of a DNS master file, taken from my own “pcguide.com” server (slightly modified), hosted by (and DNS information provided by) the fine folks at pair.com. Note the use of “@” as a short-cut to mean “this domain” (“pcguide.com”):