This slide contains details about domain name servers (DNS). It also contains Resolution of the Name Servers with Domain Name Structure with statistics table. The process of Name resolution is also explained with Recursive and iterative resolution processes.

2. What is DNS?
The global database system for
Internet addressing, mail and
other information.

3. Concept of domains and sub-domains.
 Domain management is distributed.
 DNS servers maps domain names to IP
addresses.

4. Top Level Domains
• com – Commercial
• org – Non-profit
• net – Network
service
provider
• gov – US govt.
• mil – military
• edu – Education
• au – Australian
• at – Austrian
• ca – Canadian
• dk – Dutch
• fr – French
• de – German
• in – Indian
• it – Italian
• jp – Japanese
• kr – Korean
• nz – New Zealand
• es – Spanish
• tw – Taiwanese
• uk – British or Irish
• us – U.S.

5. Domain Name Structure
 Domain names are arranged in a
hierarchical tree-like structure.

6. Some Statistics

7. Name Resolution Process
 The commonly used server is BIND
(Berkeley Internal Name Domain).
*Runs under UNIX as a process called
named.
 When an application needs some
information from the server, it invokes
the DNS name resolver.
*DNS translates a fully qualified domain
name into the corresponding IP address.
*Using the command nslookup.

8. Name Resolution Process
 If the name server does not have the
information locally, it asks its primary
server, and so on.
 For redundancy, each host may also
have one or more secondary name
servers which may be queried when
the primary fails.

9. Hierarchy of Name Servers

10. Recursive Name Resolution

11. Recursive Name Resolution
 The client(resolver) can ask for a recursive answer from
a name server. This means that the resolver expects the
server to supply the final answer.
 If the server is the authority for the domain name, it
checks its database and responds.
 If the server is not the authority, it sends the request to
another server(The Parent Usually) and waits for the
response.
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12. Iterative Name Resolution

13. Iterative Name Resolution
 Client sequentially sends queries to
DNS servers and receives response.
*If response is negative, the DNS server
to query next is also returned.
*Unlike recursive name resolution, where
only one response is finally returned
back to the client.

14. THANK YOU !