Kapil Khatiwada

What is the Internet?Network of networks

Uses the standardized Internet Protocol Suite(TCP/IP).

Millions of private and public, academic, business and govt. networks of local to global scope.

Linked by copper wires, fiber-optic cables, wireless connections, and other technologies.

A network of computers connected to each other.

What is the Internet?

How do they Connect?

Computers needed to know which computer they were connecting to, with the help of unique number – an IP (Internet Protocol) number.

Ex. 121.245.078.2 Greater numbers of users demand for an easier

system and one that was less confusing.

• In the mid 1980’s the Domain Name System was implemented and the initial top-level domain names, including .com, .net, and .org, were introduced.

• Suddenly 121.245.078.2 became 'company.com'.

Foundation Of DNS

DNS Definition

The Internet users use DNS to reference anything by name on the Internet.

The mechanism by which Internet software translates names to addresses and vice versa.

DNS Definition

IP assigns 32-bit addresses to hosts (interfaces) – Binary addresses are easy for computers to manage .– All applications use IP addresses through the TCP/IP

protocol software.– Difficult for humans to remember.

Domain names comprise a hierarchy so that names are unique, easy to remember.

Domain Names

A domain name is the sequence of labels from a node to the root, separated by dots (“.”s), read left to right.

Example domain names:– www.filehippo.com– www.bbc.co.uk

Parts of a Domain Name

A domain name usually consists of two or more parts (technically labels), which are separated by dots, such as filehippo.com

DNS Naming Structure

http://www.filehippo.com

Top level domains

2nd Level Domains

SERVER

Top-Level Domains (TLDs)

Second-Level Domains

Within every top-level domain there is a huge list of 2nd level domains

For example, in the .COM second-level domain, we've got:

yahoo msn microsoft plus millions of others...

Name Servers Also called a DNS server

Manages a massive database that maps domain names to IP addresses.

Servers are distributed widely on the Internet.

Iterative and Recursive Name Servers• Iterative servers can only answer information they know

or have cached.

• Recursive know how to ask others for information.

DNS Naming Structure

http://www.nccs.edu.np

2nd level domains3rd Level DomainsSERVER

ccTLD

How DNS Servers work(web)

Step 1: Your PC sends a resolution request to its configured DNS Server, typically at your ISP.

Your PC

ISP “Recursive” DNS server

Tell me the Address of “www.google.com”

You type http://www.google.com into your web browser and hit enter.

Step 2: Your ISPs recursive name server starts by asking one of the root servers predefined in its “hints” file.

Tell me the Address of “www.google.com”

ISP “Recursive” DNS serverRoot Servers

I don’t know the address but I know who’s authoritative for the ”com”

domain ask them

Step 3: Your ISPs recursive name server then asks one of the “com” name servers as directed.

ISP “Recursive” DNS server“com” DNS servers

Tell me the Address of “www.google.com”

I don’t know the address but I know who’s authoritative for the

”google.com” domain ask them

Step 4: Your ISPs recursive name server then asks one of the “google.com” name servers as directed.

ISP “Recursive” DNS server google.com DNS server

Tell me the Address of “www.google.com”

The Address of www.google.com is 216.239.53.99

Step 5: ISP DNS server then send the answer back to your PC. The DNS server will “remember” the answer for a period of time.

Your PC

ISP “Recursive” DNS server

The Address of www.google.com is 216.239.53.99

Step 6: Your PC can then make the actual HTTP request to the web server.

Your PC

www.google.com web server

Here it is!

Thank you!

That’s ALL!