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Table Of Contents  The TCP/IP Guide
 9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)
      9  Name Systems and TCP/IP Name Registration and Name Resolution
           9  TCP/IP Name Systems: Host Tables and Domain Name System (DNS)
                9  TCP/IP Domain Name System (DNS)
                     9  DNS Name Servers and Name Resolution
                          9  DNS Messaging and Message, Resource Record and Master File Formats

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DNS Name Notation and Message Compression Technique
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Pages in Current Topic/Section
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DNS Changes To Support IP Version 6
Next Topic/Section

DNS Master File Format
(Page 4 of 4)

Specific Resource Record Syntax and Examples

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 “”:

Table 179: DNS Master File Format Syntax and Examples

Resource Record Text Code

Resource Record Type

Resource Record Format / Example



<domain-name> [<ttl>] IN A <ip-address> IN A ; A FQDN.
admin2 IN A ; A PQDN equivalent to


Name Server

<domain-name> [<ttl>] IN NS <name-server-name> IN NS ; Secondary NS


Canonical Name

<domain-name> [<ttl>] IN CNAME <canonical-name>

www IN CNAME bigserver ; is really


Start Of Authority

<domain-name> [<ttl>] IN SOA <m-name> <r-name> (
<default-ttl>) IN SOA (
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.



<reverse-domain-name> [<ttl>] IN PTR <domain-name> IN PTR


Mail Exchange

<domain-name> [<ttl>] IN MX <preference-value> <exchange-name> IN MX 10
IN MX 20



<domain-name> [<ttl>] IN TXT <text-information> 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 “” server (slightly modified), hosted by (and DNS information provided by) the fine folks at Note the use of “@” as a short-cut to mean “this domain” (“”):

Table 180: Sample DNS Master File

@ IN SOA (
2001072300 ; Serial
3600 ; Refresh
300 ; Retry
604800 ; Expire
3600 ) ; Minimum


localhost IN A
@ IN A
IN MX 50

www IN CNAME @
ftp IN CNAME @
mail IN CNAME @
relay IN CNAME


Previous Topic/Section
DNS Name Notation and Message Compression Technique
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Pages in Current Topic/Section
Next Page
DNS Changes To Support IP Version 6
Next Topic/Section

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Version 3.0 - Version Date: September 20, 2005

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