This document provides an overview of the Domain Name System (DNS). It describes how DNS uses domain names to map to IP addresses in a hierarchical structure. Key points include:
- DNS allows users to use domain names like "example.com" instead of numeric IP addresses for easier identification of internet hosts.
- DNS information is stored across multiple name servers to prevent a single point of failure.
- The domain name space is divided into generic, country code, and inverse domains to organize names by usage and map addresses to names.
- Domain names are read from right to left with the top-level domain at the far right, working left through more specific subdomains.
3. Introduction
Domain name system is a client server application that identifies each host on
the internet, with a unique user friendly name.
Domain name system is a method to identifying hosts with user friendly names
instead of ip addresses. Because to remember numeric addresses are difficult
compare to names.
In Domain Name System names must be unique because the addresses are
unique.
Each Domain is partitioned into sub domains.
Once an Organization assigned domain name, the name is reserved for the
Organization, means no other Organization will be assigned the same name.
4. To map a name into IP address, an application program calls a library
procedure called the Resolver, passing it the name as a Parameter. The
Resolver sends a UDP packet to local DNS server, which then looks up the
name and returns the IP address to the resolver, which then returns it to the
caller process.
Domain names are always read from the bottom to top.
5. Example Of Domain Name
Lable
Edu
Fhda
Atc
Chalanger
Edu.
Fhda.edu
Atc.Fhda.edu
Challenger.Atc.Fhda.edu
6. Name Server
Information contained in the domain name system must be stored. It is very
difficult and not reliable to have just one computer store such large information.
To solve above problem, we have to distribute the information among many
computer called DNS servers.
The hierarchy of servers shown beside:
7. DNS in Internet
In the internet, domain name space is divided into 3 different section.
1. Generic domain
2. Country domain
3. Inverse domain
8. 1. Generic Domain
Generic domain defines registered host according to their generic behavior.
Each node in the tree defines a domain.
9. Com Commercial Organization
Edu Educational Institutions
Gov Government Institutions
Int International Organization
Mil Military Groups
Net Network Organization
Org Non profit Organization
10. 2. Country Domain
The Country domain uses a two-character abbreviation in place of three
character abbreviation at first level.
11. 3. Inverse Domain
The inverse domain is used to map address to a name.
When a server has received a request from a client to do a task,
server lists only the IP address of the client. To determine if the
client is on the authorized list, the server can send a query to the
inverse DNS server and ask for a mapping of address to name.
The inverse domain is added to the domain name space with the
first-level node called arpa. (Advanced Research Projects Agency)
The second level is also one single node named in-addr.
(for inverse address) The rest of the domain defines IP address.
An ip address such as 132.34.45.121(class B address) this
is read as 121.45.34.132 in-addr arpa.
132.34 45 . 12 = ip address of class B
net id subnet id host id