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Chapter 18

Domain NameSystem(DNS)

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CONTENTSCONTENTS• NAME SPACE• DOMAIN NAME SPACE• DISTRIBUTION OF NAME SPACE• DNS IN THE INTERNET• RESOLUTION• DNS MESSAGES• TYPES OF RECORDS• COMPRESSION• EXAMPLES• DDNS• ENCAPSULATION

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NAME SPACE

18.118.1

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DOMAINNAMESPACE

18.218.2

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Figure 18-1

Domain name space

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Figure 18-2

Domain namesand labels

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Figure 18-3

FQDN and PQDN

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Figure 18-4

Domains

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DISTRIBUTION OF

NAME SPACE

18.318.3

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Figure 18-5

Hierarchy of name servers

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Figure 18-6

Zones and domains

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A primary server loads all information from A primary server loads all information from the disk file; the secondary server loads the disk file; the secondary server loads

all information from the the primary server. all information from the the primary server. When the primary downloads information When the primary downloads information

from the secondary, it is called from the secondary, it is called zone transfer.zone transfer.

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DNS IN THE

INTERNET

18.418.4

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Figure 18-7DNS in the Internet

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Figure 18-8

Generic domains

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Figure 18-9

Country domains

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Figure 18-10

Inverse domain

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RESOLUTION

18.518.5

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Figure 18-11

Recursive resolution

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Figure 18-12Iterative resolution

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DNSMESSAGES

18.618.6

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Figure 18-13

DNS messages

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Figure 18-14

Query and response messages

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Figure 18-15

Header format

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Figure 18-16

QR: Query/ResponseOpCode: 0 standard, 1 inverse, 2 server statusAA: AuthoritativeTC: TruncatedRD: Recursion DesiredRA: Recursion AvailablerCode: Status of the error

Flags fields

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TYPESOF

RECORDS

18.718.7

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Figure 18-17

Question record format

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Figure 18-18

admin.atc.fhda.edu.

Query name format

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Figure 18-19

Resource record format

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COMPRESSION

18.818.8

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Figure 18-20

Format of an offset pointer

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EXAMPLES

18.918.9

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Example 1Example 1

A resolver sends a query message to a local server to find the IP address for the host “chal.fhda.edu.”. We discuss the query and response messages separately.

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Figure 18-21

Example of a query message

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Figure 18-22 Example of a response message

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Example 2Example 2

An FTP server has received a packet from an FTP client with IP address 153.2.7.9. The FTP server wants to verify that the FTP client is an authorized client.

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Figure 18-23

Example of inverse query message

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Figure 18-24

Example of inverseresponse message

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DDNS

18.1018.10

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ENCAPSULATION

18.1118.11

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DNS can use the services of DNS can use the services of UDP or TCP UDP or TCP

using the well-known port 53.using the well-known port 53.