The document discusses the Domain Name System (DNS), which maps host names to their corresponding IP addresses. DNS is an internet directory service that acts as a client-server application to provide name mapping, as IP addresses are difficult to remember and can change. Historically, name mapping was done using a host file on each computer, but as the internet grew this became impractical, leading to the distributed DNS system with a hierarchy of root, top-level domain, and authoritative name servers. DNS supports two types of queries - recursive queries where a server resolves a query itself, and iterative queries where a server refers the query to another name server.

1. Fahem Ahmed
Id : 133-15-3008
DOMAIN NAME SYSTEM (DNS)

2. WHAT IS DNS ?

3. • Internet Directory Service.
• A client server application that maps host names into their
corresponding Ip addresses.
• Mapping host names into their corresponding IP addresses is
called Name mapping.

4. WHY WE NEED TO USE NAMES INSTEAD OF IP NUMBERS ?

5. • IP Addresses Are Difficult To Remember.
• IP Addresses Can Change.

6. Problem : Network only understand Numeric
addresses.

7. HISTORY OF DNS
When the Internet was small, mapping was done using a host file. The host file
had only two columns one for the name and one for the address. Every host
could store the host file on its disk and update it periodically from a master host
file.
Distributed Service

8. HIERARCHY OF NAME SERVERS:
root server
com servergov serveredu serverorg server
uci.edu
server
.virginia.edu
server
cs.virginia.edu
server

9. There are two types of queries:
• Recursive queries.
• Iterative (non-recursive) queries.

10. • Recursive query : When the name server of a host cannot resolve a
query,the server issues a query to resolve the query.
• Iterative queries : When the name server of a host cannot resolve a query it
sends a referral to another server.

11. Thank You !