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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

Previous Topic/Section
DNS Message Header and Question Section Format
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45
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DNS Name Notation and Message Compression Technique
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DNS Message Resource Record Field Formats
(Page 3 of 5)

RData Field Formats For Common Resource Records

The RData field consists of one or more subfields that carry the actual “payload” for the resource record. Below is a list of the most common resource record types. For each I have indicated the resource record text code, name, and Type value, provided a brief summary of the resource record’s use, and shown the structure of the RData field in a table:

A / Address Resource Record (Type Value 1)

This is the primary resource record type in DNS; it contains a 32-bit IP address associated with a domain name, as shown in Table 172.


Table 172: DNS Address Resource Record Data Format

Subfield Name

Size (bytes)

Description

Address

4

Address: The 32-bit IP address corresponding to this record's named object.


NS / Name Server Resource Record (Type Value 2)

In this record, the data field carries the domain Carries the domain name of a name server (Table 173).


Table 173: DNS Name Server Resource Record Data Format

Subfield Name

Size (bytes)

Description

NSDName

Variable

Name Server Domain Name: A variable-length name of a name server that should be authoritative for this record's named object. Like all names, this name is encoded using standard DNS name notation.

A request for this resource record type normally results in an A record for the name server specified also being returned in the Additional section of the response, if available.


CName / Canonical Name Resource Record (Type Value 5)

The data field contains the real name of an a named object that has been referenced using an alias (Table 174).


Table 174: DNS Canonical Name Resource Record Data Format

Subfield Name

Size (bytes)

Description

CName

Variable

Canonical Name: The canonical (real) name of the named object. This name is then resolved using the standard DNS resolution procedure to get the address for the originally-specified name.


Previous Topic/Section
DNS Message Header and Question Section Format
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Pages in Current Topic/Section
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3
45
Next Page
DNS Name Notation and Message Compression Technique
Next Topic/Section

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