1. Domain Name System (DNS)

2. Names For Computers
Humans prefer pronounceable names rather than numeric addresses
Two possibilities
Flat namespace
Hierarchical namespace

3. Hierarchical namespace
Two possibilities
According to network topology
By organizational structure (independent of physical networks)
Internet uses……?

4. Internet Domain Names Flexible hierarchy
Universal naming scheme (same everywhere)
Each organization determines internal naming structure
Mechanism known as Domain Name System (DNS)
Name assigned to a computer known as domain name

5. Set of labels separated by delimiter character (period)
Eg : mail.google.com
Three labels: mail, google, and com
Top-level domain is com

6. examples of the global top-level domain names currently in use

7. Original Top-Level Domains
Three domains considered generic .com .net .org

8. New Top-Level Domains
Internet Corporation for Assigned Names and Numbers (ICANN)

9. Illustration Of Part Of The DNS Tree

10. DNS
Authority For Names
Authority delegated down the tree

11. Name Syntax And Type
Domain Name System is quite general
multiple naming hierarchies embedded in one system
A given name may map to more than one item in the domain system.

12. DNS Database
The client specifies the type of object desired when resolving a name, and the server returns objects of that type

13. DNS Database Record has (name, class)
Class specifies type of object (e.g., computer, exchanger)

14. Mapping Domain Names To Addresses
DNS uses a set of on-line servers
Servers arranged in tree
Given server can handle entire subtree
Example: ISP manages domain names for its clients

15. Mapping Domain Names To Addresses
DNS server known as name server
supplies name-to-address translation, mapping from domain names to IP addresses.
DNS client software known as resolver

16. Mapping Domain Names To Addresses

17. Mapping Domain Names To Addresses
In Practice
Single server can handle multiple levels of the naming tree
Example: root server handles all top- level domains

18. Domain Name Resolution
Conceptually, must search from root of tree downward
In practice
Every name server knows location of a root server
Only contacts root if no subdomain known
Lookup always starts with local server first (host can learn address of DNS server from DHCP)

19. Domain Name Resolution
Efficient Translation
Most lookups refer to local names
Name-to-address bindings change infrequently
User is likely to repeat same lookup

20. Domain Name Resolution
To increase efficiency
Initial contact begins with local name server
Every server caches answers (owner specifies cache timeout)

21. Domain Server Message Format

22. interpretation of bits in the PARAMETER field

23. The format of entries in the QUESTION SECTION

24. format of a resource record
ANSWER SECTION, AUTHORITY SECTION, and ADDITIONAL INFORMATION SECTION fields consists of a set of resource records that describe domain names and mappings.

25. Abbreviation Of Domain Names
method of shortening names when the resolving process can supply part of the name automatically
Telephone numbers
Area code – Number
Client configured with suffix list – . cs . purdue . edu – . cc . purdue . edu – . purdue . edu – null

26. Abbreviation Of Domain Names
User enters abbreviation xinu
Client tries the following in order
xinu. cs . purdue . edu
xinu. cc . purdue . edu
xinu. purdue . edu
xinu

27. Inverse Query
Map in reverse direction
Excessive overhead
May not have unique answer
Not used in practice

28. Pointer Query Special case of inverse mapping
Convert IP address to domain name
Trick: write IP address as a string and look up as a name

29. IPv4 address format:
aaa.bbb.ccc.ddd
To form a pointer query, the client rearranges the dotted decimal representation of the address into a string of the form:
ddd.ccc.bbb.aaa.in-addr.arpa

30. Object Types That DNS Supports

31. IA 2
Interior Gateway Protocol (RIP, OSPF, HELLO), Routing Information Protocol (RIP), Combining RIP, HELLO, and EGP, Routing with partial information.
Internet multicasting, Mobile IP, Private Network Interconnection, Client Server Model,Sock Interface. Bootstrap and autoconfiguration: BOOTP,DHCP.