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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 Message Header and Question Section Format
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 DNS Name Notation and Message Compression Technique
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DNS Message Resource Record Field Formats
(Page 2 of 5)

DNS Common Resource Record Format

There are certain types of information that are common to all resource records, and others that are unique to each type of record. To handle this, all resource records are represented using a common field format, which contains a single RData field that varies by record type. The common resource record format is described in Table 171 and Figure 250.


Table 171: DNS Common Resource Record Format

Field Name

Size (bytes)

Description

Name

Variable

Name: Contains the object, domain or zone name that is the subject of the resource record, encoded using standard DNS name notation. All of the information in the resource record is associated with this object, which I call the named object for the record.

Type

2

Type: A code value specifying the type of resource record. The type values for the most common kinds of resource records are shown in Table 166 and also in the list of resource record details in this topic.

Class

2

Class: Specifies the class of the resource record being requested, normally the value 1 for Internet (“IN”). See the end of the topic on classes and resource record types for an explanation.

TTL

4

Time To Live: Specifies the number of seconds that the record should be retained in the cache of the device reading the record. See the topic on DNS name server caching for a full explanation. A value of zero means “use this information for the current name resolution only; do not cache it”.

RDLength

2

Resource Data Length: Indicates the size of the RData field, in bytes.

RData

Variable

Resource Data: The data portion of the resource record.


Figure 250: DNS Common Resource Record Format

 

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