Download - 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