CS101

How the Internet Works

When did the Internet start?

• The Internet was born in 1969 with the invention of ARPANET

• ARPANET was a research project funded by the Defense Department

• The network had to be able to operate even if part of it was destroyed

When did the WWW start?

• The Internet is the hardware of the worlds largest network of computers.

• The WWW is one of the functions invented to use the hardware of the largest computer network in the world.

• This means the Internet is older then the WWW– WWW was not invented until 1991

• On August 6, 1991, Tim Berners-Lee posted a short summary of the World Wide Web project on the alt.hypertext newsgroup. This date also marked the debut of the Web as a publicly available service on the Internet.

How does information move about on a network? Packet Switching!

• Information represented as zeros and ones (email, web pages, IM, files, video, sound, etc) is broken into packets.

• Each packet has a send address, return address, and an order number

• Each packet then moves across the network finding the best way to its send address (routers and switches help out).

• Not all packets have to go the same route• Once they get to their destination the packets put

themselves back in order• This system allows the network to keep functioning

even if part of it is not working

How do the packets know where to go?• When your computer (or network) becomes

part of the Internet it has to agree to the TCP/IP protocols

• The TCP/IP protocols tell the packets what form they should be in so all computers on the network will understand the information

• The TCP/IP protocols makes sure that every computer has a unique IP (Internet Protocol) address

• The packets move from one IP address to the destination IP address

What is an IP address?• There are two types of IP addresses• IP version 4 (Ipv4) = the older system that is still

the most widely used– Ipv4address = 4 numbers between 0 and 255 separated

by periods (for example 130.157.3.70)• A 32 bit number

• IP version 6 (Ipv6) = the new system created because we are running out of numbers– Ipv6 address = are 128-bit numbers and are

conventionally expressed using hexadecimal strings (for example 1080:0:0:0:8:800:200C:417A)

• You can find your IP address in System Information (Win) or System Profiler (Mac)

Who is in charge of IP addresses?

• IP address are assigned by IANA (Internet Assigned Number Authority)

• The IANA delegates the responsibility for this part of the world to ARIN (American Registry for Internet Numbers)

• ARIN delegates the responsibility to accredited companies who register with InterNIC

How do you get an IP address?

• Two ways to get an IP address– 1) From your ISP (Internet Service Provider)– 2) From the DNS (Domain Name System)

IP address from your ISP

• Your ISP will assign your computer an IP address when you contact their computer to gain access to the Internet

• Most of the time you will get a dynamic IP address– Different address each time you access the

Internet

• You can pay more and get a IP static address– Same IP address each time you access the

Internet

How do I get an IP address all by myself?

• You use an accredited registrar for the Domain Name System to first find some text that no else has used for their domain on the Internet

• Once you find your unique text you then register that unique text with the domain name system which assigns a unique IP address to the text

• The text and IP address that it is paired with are then stored in the Domain Name System database so that no one else can use it

How do computers find each other using IP addresses?

• Computers use the Domain Name System (DNS) to find each other.

• The DNS is managed by IANA.• The DNS breaks all the computers on the

Internet into top level domains– .com, .edu, .net, .org, .uk, .net, etc

• Each computer in a domain has a unique IP address attached to a unique string of text– sonoma.edu is attached to 130.157.3.70– You can lookup an IP address at this website:

• http://cqcounter.com/whois/

So how does the Domain Name System work?

When you enter an address such as – http://www.sonoma.edu into your browser the

DNS helps your computer contact the other computer by using the following method:

(Explanation given in class using the whiteboard.)

• If you missed the lecture then read about a web address on the following web page

– http://www.internic.net/faqs/authoritative-dns.html