3b. dns(29 Slide)

Domain NameSystem(DNS)

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

1. Domain name space

Domain namesand labels

FQDN and PQDN

Domains

Hierarchy of name servers

2. DISTRIBUTION OF NAME SPACE

Zones and domains

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.

3. DNS in the Internet

Generic domains

Country domains

Inverse domain

a. Recursive resolution

4. RESOLUTION

b. Iterative resolution

5. DNS messages

Query and response messages

Header format

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

Flags fields

a. Question record format

6. TYPES OF RECORDS

admin.atc.fhda.edu.

b. Query name format

c. Resource record format

Format of an offset pointer

7. COMPRESSION

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.

8. EXAMPLES

Example of a query message

Example of a response message

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.

Example of inverse query message

Example of inverseresponse message