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 Information | HINFO | Describes the architecture and operating system of a host in the database |
Canonical Name | CNAME | Defines an alias, or alternative name, for a host |
Mail Exchange | MX | Defines a mail exchange host |
Name Server | NS | Declares 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.
dnsmaster.corporation.com.
( 19980416 1800 300 604800 1800 )
IN NS dns1.corporation.com.
IN NS dns2.corporation.com.
$ORIGIN corporation.com.
morgan IN A 196.143.12.200
IN HINFO "PPC" "MacOS"
vanderbilt IN A 196.143.12.201
IN HINFO "Sparc" "Solaris"
www IN CNAME vanderbilt.corporation.com.
rockerfeller IN A 196.143.12.202
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.
dnsmaster.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