The Internet!!

The Internet is not the only network!

• Can connect a bunch of computers without connecting to the Internet, and those computers can communicate with each other

• SCU has a local network “Novell”• An internet is a network of networks– The Internet is an internet

• You can be connected to more than one network at the same time!

The www is not the whole Internet!

• It’s a series of tubes!• Email is not always web-based– Thunderbird, outlook not web-based, use the Internet to send emails as data

• Your Netflix streaming through your Blu-Ray player is not the web, but it uses the Internet to send movies as data

• Xbox Live• Ssh uses the Internet to send commands as data• The web uses the Internet to send webpages as

data

http://en.wikipedia.org/wiki/World_wide_web

• “The World Wide Web (abbreviated as WWW or W3,[2] commonly known as the web), is a system of interlinked hypertext documents accessed via the Internet. With a web browser, one can view web pages that may contain text, images, videos, and other multimedia, and navigate between them via hyperlinks.”

What is the Internet?

Not magic Mainly, a bunch of cablesMostly privately ownedYou pay your access ISP (Internet Service Provider)And they make arrangements with other (higher-tier) ISPs to use their cables to get your traffic where it’s goinghttp://en.wikipedia.org/wiki/Tier_1_network

What is the Internet?

• Yes, even across the ocean! These are also privately owned; AT&T, etc http://commons.wikimedia.org/wiki/File:Undersea_cable_laying.gif

• The .com bubble of the late 1990s led to an excess of bandwidth

• Where no cable: Satellite (slow, expensive, unreliable)

How do I connect to the Internet?

• Computer/device access point (for wireless) ISP connects you to “the Internet”Routers send your traffic along different

cables (that belong to ISPs your ISP is friends with)

The computer out there that you’re trying to connect to

What is this other computer I’m connecting to?

• Usually, a server (web (wikipedia), data (netflix streaming), email)

If Jane is in Sunnyvale, and Bob is in Germany

• And Jane sends Bob an email from her jsmith@scu.edu email address to Bob’s banderson@gmail.com email address

• When Bob reads the email message, what can you say about the path the bits have taken to get to him?

How does the Internet know how to find everything?!?!?

• Addresses!• Every device connected to the Internet has a unique

address that looks something like• 129.210.115.4 (Google “What is my IP?”)• You’ll notice that it changes – usually you’re assigned a

new IP (Internet Protocol) address every time you connect

• But not servers – The Internet needs to be able to find them, so they have static IPs

• IP address has meaning; different ISPs control different blocks of IP addresses– This is how routers know where to send your packet so it

eventually reaches its destination– 500 El Camino Real, Santa Clara, CA, USA

What does http://www.scu.edu have to do with 129.210.115.4?

• I wouldn’t want to have to type 129.210.115.4 every time I wanted to go to the SCU webpage!

• http://www.scu.edu is the human-readable name that maps to the static IP address of SCU’s web server (Something like 129.210.115.4)

• So how does http://www.scu.edu get translated into 129.210.115.4?

• You must register this correspondence with the Domain Name System servers

• Servers whose sole purpose is to translate URLs (uniform resource locator, aka web address) into IP addresses

Regional Internet Registires

• Managed by ICANN• Each allocates blocks of IP addresses to local ISPs

Domain Name System (DNSs)• http://en.wikipedia.org/

wiki/Root_name_server• When you try to go

somewhere on the www, the first thing is a DNS lookup to get the IP address– DNS Server not found error

• Then you can establish a connection with the web server at that IP address

• What if these servers go down?!?!?!

Anatomy of a URL

• There is a web server for http://www.scu.edu• That web server is responsible for getting you

anywhere that ends in .scu.edu• math.scu.edu/~linnell

What is sent and how?And what does this have to do with security?

• Once you find the computer you want to connect to, you negotiate a connection– Authentication

• Then the information to be sent is broken up into packets, each of which has information about where it came from, where it’s going, and who sent it.– Encryption, https