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Lesson 9 Zone files and Resource Records
Objective Match each Resource Record abbreviation with a description of its purpose.

Zone Files and Resource Records

How that we have an overview of how DNS operates, we will focus on the actual form of the data in the DNS database.
As mentioned earlier, the data is stored in files, called zone files, which reside on the hosts running authoritative name servers for the zone. The individualrecords in the zone files are called Resource Records (RRs) and come in various types, as shown in the table below:

Resource Record Type Abbreviation Purpose
State of Authority SOA Sets basic parameters for a zone, and establishes responsible parties
Address A Specifies a name-to-address mapping
Pointer PTR Specifies an address-to-name mapping
Host InformationHINFODescribes the architecture and operating system of a host in the database
Canonical NameCNAMEDefines an alias, or alternative name, for a host
Mail ExchangeMXDefines a mail exchange host
Name ServerNSDeclares a name server for a zone

We will examine each of these Resource Record types later in this module. We will discuss MX records later in this course.

View the following example to examine these zone files.

View Example: zone files

Zone file for corporation.com:
$ORIGIN  com.
corporation  IN SOA   server.corporation.com.
( 19980416 1800 300 604800 1800 )
             IN      NS     dns1.corporation.com.
             IN      NS     dns2.corporation.com.

$ORIGIN  corporation.com.
morgan       IN      A
             IN      HINFO    "PPC"  "MacOS"
vanderbilt   IN      A
             IN      HINFO    "Sparc"  "Solaris"
www          IN      CNAME    vanderbilt.corporation.com.
rockerfeller IN      A
             IN      HINFO    "Intel"  "Linux"

Zone file for 12.143.196.in-addr.arpa:
$ORIGIN  143.196.in-addr.arpa.
12  IN     SOA      server.corporation.com.
                    ( 19980302 1800 300 604800 1800 )
    IN     NS       dns1.corporation.com.
    IN     NS       dns2.corporation.com.
$ORIGIN  12.143.196.IN-ADDR.ARPA.
200    IN     PTR   morgan.corporation.com.
201    IN     PTR   vanderbilt.corporation.com.
202    IN     PTR   rockerfeller.corporation.com.

Hypothetical Zone Files

Let us look at hypothetical zone files for an organization called Corporation, Inc. Corporation, Inc. administers two DNS zones.
The first is the corporation .com zone. The second is the reverse lookup zone 12.143.196.in-addr.arpa derived from Corporation's Class C network address 196.143.12.

Resource Record Abbreviations

Click the link below to read about Resource Record abbreviations with their definitions.
Resource Record Abbreviations