Transcript CS101 Lecture

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?
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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