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DOUG LLOYD: If you've
been watching these videos

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in the order which we recommend,
we're about to undergo

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bit of a culture shift.

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Because now, we're going to start
talking about the internet and web

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technologies.

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So up until now, we've
really been doing a lot of C.

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>> And when we've been
running our programs,

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we have been running them
from the command line.

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That's pretty much how the users have
been interacting with the programs

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that we write.

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They pick something to prompt, something
happens in the terminal window,

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and then it's done.

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>> Sometimes you might have persistent
data that remains afterwards.

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But that's pretty much it.

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It's at the command line.

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It's the only way the user can interact.

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From this point forward,
we're going to start

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transitioning so that the users
can interact with our websites.

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So we're going to be writing
websites, which aren't written in C,

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but are written in a variety of other
programming languages, including PHP,

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and it's sort of helper languages,
HTML, CSS, and the like.

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So we're going to start
talking about those things.

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>> Before we get into web
programming itself,

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I think it's probably a good
idea to take a step back and talk

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about how computers and
humans interact over the web.

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So this video is really a primer,
a basic guide, to the internet.

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Now, the caveat here is the
CS50 is not a networking class.

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So what we're going to be talking
about here is pretty high level.

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We're not going to
get into any low level

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details of how all this stuff works.

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If you're interested
in that, I'd strongly

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recommend taking a class
on computer networking.

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And we might even tell
white lie or two just

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for the purposes of making the
general understanding clear.

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>> So with that said, let's talk about
how we interact with the internet.

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So here we are.

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Here's us.

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We're pretty looking forward to
getting onto the internet, which

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as we all know, is chock full of cats.

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>> Now do we just connect to
the internet like this?

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Well, probably not.

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Intuitively, you know
that, say for example,

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when you change your Wi-Fi
network on your computer,

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you don't see one called internet
unless that just so happens

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to be the name of your local Wi-Fi.

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Right?

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>> It's usually something like home.

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Or if you're at work, it might
be the name of your company.

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There's not just one
option called internet.

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And so something or some
things exist in between when

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we want to connect to the internet.

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What are some of those things?

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Well, we're going to talk about that.

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We're also going to talk about
some of the important things

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we need in order to be able
to connect to the internet.

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And the first of these
things is an IP address.

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So you've probably heard
the term IP address before.

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What does it mean?

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Well, an IP address is
basically a unique identifier

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of your computer on a network.

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Just like every home or
office has a unique address

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to which one could send a mail.

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>> Similarly, every computer if it
wants to receive data or send data,

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needs to have a unique address.

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So that when information
is sent or received,

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it's being sent from or received
to the correct location.

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This addressing scheme, as I
said, is called IP addressing.

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IP is stands for Internet Protocol,
which we'll talk about again shortly.

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>> Now, what does IP addressing look like?

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Well, the scheme basically was,
when it was first implemented,

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to give every computer
a unique 32-bit address.

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That's a lot of bits.

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That's 4 billion addresses.

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>> And generally, instead of using
hexadecimal notation, which

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we've used previously in the context of
pointers in C to talk about addresses,

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we usually represent IP
addresses in a little bit more

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of a human friendly
way, representing them

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as four clusters of 8 bits
represented as decimal numbers.

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Because humans don't frequently speak
hexadecimal, unless you're programming.

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But people who use the internet
aren't necessarily programmers.

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>> And so making it easy
and accessible for them

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to be able to talk about what their
IP address is in case they maybe

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need to call up somebody
to troubleshoot something,

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it's better to make it in the more
common conventional decimal number

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format.

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And so an IP address just looks
pretty much like this, w.x.y.z,

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where each one of those letters
represents a non-negative value

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in the range of 0 to 255.

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Recall that an 8-bit number
can hold 256 distinct values.

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>> And so that's why our range is 0 to 255.

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And we have four clusters of 8
bits for a grand total of 32 bits.

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And so an IP address might
look something like this.

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This is sort of a generic
default IP address, 123.45.67.89.

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All of them are in the range of 0 to
255, so that's a valid IP address.

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>> Here at Harvard University, all of
our IP addresses start with 140.247.

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That's just the way that the IP
addresses in this geographic area

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have been assigned.

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And so this might be an IP address
that might exist here at Harvard.

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>> So as I said, if every IP address
is 32 bits, we have about 4 billion

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to give out, a little
more than 4 billion.

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But we can kind of see a problem, right?

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What's the world population right now?

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>> Well, it's somewhere
north of 7 billion people.

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And in the Western world
at least, most people

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have more than one device
capable of internet connectivity.

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I have one right here.

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And I have another one in my pocket.

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And I have one back in my office.

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>> And so that's three.

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And that doesn't even count the
ones that I have at home, too.

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And so that's kind of a problem, right?

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We have at least 7 billion people
and only 4 billion addresses.

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>> And every device is supposed
to be uniquely identified.

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We have developed some workarounds
to deal with this problem,

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something called a private
IP address, which we're not

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going to get into in this video.

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But basically, it allows further the
web, the internet, to kind of fake

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out a little bit that you have a unique
address by having private addresses

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and then funneling them through
one single address, which

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is shared by many different computers.

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>> But that's really not a long term fix.

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Even that fixed isn't
going to last forever.

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And so we need to have a different
way of dealing with this.

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>> So as I said, we had about 4 billion.

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But that's not going to
be good enough, right?

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And so the way that it has
been decided there we're

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going to deal with this is
to make longer IP addresses.

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Instead of 32-bit addresses, we're
going to have 128-bit addresses.

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So instead of 4 billion
addresses, we're going

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to have that huge number of addresses,
which is 340 billion billion billion

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billion, so a lot of IP addresses.

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>> And this new scheme is called IPv6
is commonly how it's referred.

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The old scheme being IPv4.

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It's a bit of a problem in
that this problem has been

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known about for a really long time.

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>> And you'll see this a lot in the
context of computers and computing.

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We're good at anticipating problems.

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But we're bad at dealing with them
even though we know about them.

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So IPv6 has been around for a while.

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And only in the last couple
years have we actually

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started phasing in these IPv6 addresses
to phase out the IPv4 addresses.

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But some places do have them.

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And they look similar
to a regular IP address.

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But they are a lot longer.

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>> So instead of now having four
clusters of 8 bytes for your address,

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we now have eight clusters of 16 bytes.

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And 8 times 16 is 128.

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And we represent these in the less
conventional hexadecimal form.

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Because having 16-bit numbers means that
instead of being a range of 0 to 255,

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We'd have a range of 0 to 65,535.

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>> And so having a bunch
of those stuck together

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would be very difficult to read.

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And so we usually use hex
just out of convenience.

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And so a typical IPv6 address
might look something like this.

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>> It's certainly a lot longer than
the IPv4 address we've seen before.

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But this would be a valid IPv6 address.

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This one is also about IPv6 address.

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>> This one happens to belong to Google.

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And notice there's a
bunch of zeros there.

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Sometimes these addresses
can get so long.

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And since we're still
pretty early in IPv6,

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sometimes there can be big chunks of
zeros in there that we don't need.

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>> If you're reading this out loud,
it's 2001.4860.4860.0.0.0.0.8844.

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It's kind of a lot, right?

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So if you see a bunch of
zeros, you might sometimes

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see an IPv6 address like this,
where they omit the zeros

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and use a double colon instead.

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This is OK, though.

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Because we know that there are
supposed to be eight distinct chunks.

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And so by implication, we see four.

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So we know that there must be four sets
of zeros like this, that fill it in.

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>> So sometimes, you might see
an IPv6 address not having

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eight separated chunks like we do here.

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You might see it looking like this.

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And that just means that
everything you don't see in

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between where that double colon
is is just zero separated.

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>> So, OK.

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We know a little bit more
about IP addresses now.

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But how do we get them?

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We can't just pick the one we want.

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If we did that, we might end up fighting
somebody for the same IP address.

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Or somebody might have
chosen it previously.

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If we try and take it, we're going
to run into a bit of a problem.

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And so we can't just pick
the IP address that we want.

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>> So the way that we get an
IP address is somewhere

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between our computer and the
internet, that big internet out there,

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there's something called a DHCP server,
a Dynamic Host Configuration Protocol

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server.

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It's a big mouthful of text.

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But really all it does is it
assigns you an IP address.

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>> Your DHCP server has a list of
addresses that it can validly assign.

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And it gives you one.

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That's pretty much all there is to it.

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Now before DHCP, this task
of assigning addresses

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fell to a system administrator.

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So an actual person would have
to manually assign your computer

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and address when you
connected to a network.

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So DHCP just sort of automates this
process of giving you an IP address.

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But that's how you get it.

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It's just a program running
somewhere between you

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and the internet that has a bank of
IP addresses that it can give out.

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And when you connect to the
network, it gives you one.

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So let's revisit this diagram.

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Somewhere between you and the
internet, there's a DHCP server.

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OK.

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So that's good.

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Now, let's talk about DNS.

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So we've talked although
these IP addresses.

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And we know that if we're
going to uniquely identify

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a device on the internet, it
has to have a unique address.

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>> And we could visit that
address if we wanted to.

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But you've probably never typed
in something like 192.168.1.0

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into your browser, right?

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You don't type in numbers
into your browser.

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You usually type in human readable names
like google.com or cs50.harvard.edu,

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right?

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>> Those aren't IP addresses, though.

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So exists this service
called the Domain Name

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System, DNS, that translates IP
addresses to human comprehensible words

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or phrases that are much more memorable
than remembering a set of four numbers

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or, soon, a set of eight
hexadecimal numbers.

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That would be really challenging, right?

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>> Think about before the
days of cell phones.

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You had your memorize your
friend's phone numbers.

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It might have gotten tough
after a little while.

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And similarly, if you want
to visit a bunch of websites,

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you probably don't want to
remember a bunch of numbers.

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You'd rather remember a bunch of words.

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>> So this mapping, this translating, of
sets of numbers to human readable names

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kind of makes DNS the
yellow pages of the web.

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And you can think about
it as if it's just

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a huge list running from 0.0.0.0 all
the way down to 255.255.255.255, which

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would be the highest possible-- that's
the full range from 0s to 255s of all 4

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billion-ish IPv4 addresses.

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00:11:25,525 --> 00:11:27,400
I made up the ones on
the top and the bottom.

238
00:11:27,400 --> 00:11:30,500
But the one in the middle there
is actually an IP address.

239
00:11:30,500 --> 00:11:38,440
So if we visited 74.125.202.138,
apparently that translates to that site

240
00:11:38,440 --> 00:11:40,490
there, io-- what the heck is that?

241
00:11:40,490 --> 00:11:46,290
Well, not every name that maps is
actually clear what it is, right?

242
00:11:46,290 --> 00:11:48,920
>> So sometimes somebody
who owns an IP address

243
00:11:48,920 --> 00:11:52,090
might name their host something
that they're actually not.

244
00:11:52,090 --> 00:11:55,442
For example, that IP address if you
went there, is actually just google.com.

245
00:11:55,442 --> 00:11:57,540
But Google has a lot
of different servers.

246
00:11:57,540 --> 00:11:59,322
>> And they can't call them all google.com.

247
00:11:59,322 --> 00:12:03,530
So they have their own
internal system for translating

248
00:12:03,530 --> 00:12:09,125
google.com to whatever server actually
is connected to that IP address.

249
00:12:09,125 --> 00:12:11,250
And then there's another
system that exists between

250
00:12:11,250 --> 00:12:15,120
to translate that gobbledygook
here to google.com.

251
00:12:15,120 --> 00:12:16,830
But we won't get into that.

252
00:12:16,830 --> 00:12:18,920
>> And similarly for
IPv6s, we're also going

253
00:12:18,920 --> 00:12:22,089
to have a yellow pages
that'll be a lot bigger.

254
00:12:22,089 --> 00:12:23,880
And similarly, in the
middle there-- it was

255
00:12:23,880 --> 00:12:26,496
tough to find an IPv6
address that was legitimate.

256
00:12:26,496 --> 00:12:27,620
But I found one for Google.

257
00:12:27,620 --> 00:12:30,460
>> But it's Google's Irish website.

258
00:12:30,460 --> 00:12:34,170
But if you went to that IPv6 address,
if your browser was IPv6 capable,

259
00:12:34,170 --> 00:12:36,940
that would bring you to
Google's Irish homepage.

260
00:12:36,940 --> 00:12:39,460
So there you go.

261
00:12:39,460 --> 00:12:41,830
>> But this isn't entirely true, right?

262
00:12:41,830 --> 00:12:43,710
This the system seems cumbersome, right?

263
00:12:43,710 --> 00:12:47,220
If there's a huge list of 4
billion things to have to look up,

264
00:12:47,220 --> 00:12:48,270
that's pretty big.

265
00:12:48,270 --> 00:12:52,634
There's no yellow pages
of the world, right?

266
00:12:52,634 --> 00:12:54,800
If you still get the yellow
pages delivered to you--

267
00:12:54,800 --> 00:12:56,841
I got mine the other day,
and I just recycled it.

268
00:12:56,841 --> 00:12:59,070
But if you do get the yellow
pages delivered to you,

269
00:12:59,070 --> 00:13:02,120
you don't get a book that's every
phone number that exists on the planet,

270
00:13:02,120 --> 00:13:02,620
right?

271
00:13:02,620 --> 00:13:05,500
You get a list of the
local phone numbers,

272
00:13:05,500 --> 00:13:07,670
the ones you're most likely to call.

273
00:13:07,670 --> 00:13:09,400
>> And that's actually what DNS is.

274
00:13:09,400 --> 00:13:12,860
If you think about it, DNS is
really the local yellow pages.

275
00:13:12,860 --> 00:13:17,350
And large DNS servers
like google.coms, they

276
00:13:17,350 --> 00:13:19,180
are actually just more
like libraries that

277
00:13:19,180 --> 00:13:25,470
have a copy of all of the local yellow
pages or all of the local DNS records.

278
00:13:25,470 --> 00:13:29,520
So there's really no one repository
of the full DNS of the internet,

279
00:13:29,520 --> 00:13:32,410
just like there's no one
yellow pages of the world.

280
00:13:32,410 --> 00:13:36,450
>> There are all these local small
scale DNSs that exist out there.

281
00:13:36,450 --> 00:13:39,010
And there are services that
aggregate them together.

282
00:13:39,010 --> 00:13:42,174
But they depend on those
smaller DNS systems

283
00:13:42,174 --> 00:13:45,340
updating their information, so that
they have the most accurate information.

284
00:13:45,340 --> 00:13:48,500
>> So again, this analogy
is large aggregating

285
00:13:48,500 --> 00:13:51,910
DNS systems are like
libraries that have a copy

286
00:13:51,910 --> 00:13:56,410
of every yellow pages of the world.

287
00:13:56,410 --> 00:13:58,350
They don't themselves
update those books.

288
00:13:58,350 --> 00:14:01,620
They depend on the books coming in,
so they can update the information

289
00:14:01,620 --> 00:14:04,560
if they need it.

290
00:14:04,560 --> 00:14:07,700
>> So the DNS system is not a giant block.

291
00:14:07,700 --> 00:14:11,026
It's decentralized across
many, many servers.

292
00:14:11,026 --> 00:14:13,400
So now we know that somewhere
between us and the internet

293
00:14:13,400 --> 00:14:18,350
there exists a DNS server
as well as a DHCP server.

294
00:14:18,350 --> 00:14:20,910
>> Now, access points,
what our access points?

295
00:14:20,910 --> 00:14:23,840
Well, access points you're probably
pretty familiar with from actually

296
00:14:23,840 --> 00:14:24,964
connecting to the internet.

297
00:14:24,964 --> 00:14:28,820
That's the network that you choose,
the home or your work network

298
00:14:28,820 --> 00:14:30,310
or what have you.

299
00:14:30,310 --> 00:14:32,597
>> And I'm generalizing the
concept of an access point

300
00:14:32,597 --> 00:14:33,930
here for purposes of this video.

301
00:14:33,930 --> 00:14:35,721
But there are actually
a lot of things that

302
00:14:35,721 --> 00:14:38,766
can be rolled up into access points.

303
00:14:38,766 --> 00:14:41,890
There are concepts of routers, which
is sort of a general term that we use.

304
00:14:41,890 --> 00:14:45,940
>> But there are also switches
and things actually called

305
00:14:45,940 --> 00:14:49,070
access points that are separate from
this general concept of an access

306
00:14:49,070 --> 00:14:49,780
point.

307
00:14:49,780 --> 00:14:54,510
But basically what
happens is with IPv4, I

308
00:14:54,510 --> 00:14:57,030
said we have this concept
of private addresses, right?

309
00:14:57,030 --> 00:15:03,680
And instead of every machine
having a unique IP address, which

310
00:15:03,680 --> 00:15:07,720
we have run out of, because
we're over 4 billion devices

311
00:15:07,720 --> 00:15:09,860
trying to connect to
the internet, what we do

312
00:15:09,860 --> 00:15:12,810
is instead assign an
IP address to a router.

313
00:15:12,810 --> 00:15:15,960
That router or access point
just in your home, for example.

314
00:15:15,960 --> 00:15:19,280
>> And the router's job as to
sort of act as a traffic cop,

315
00:15:19,280 --> 00:15:23,540
allowing everybody who's connected
to that router to use the same IP

316
00:15:23,540 --> 00:15:25,115
address to get out.

317
00:15:25,115 --> 00:15:25,990
Does that make sense?

318
00:15:25,990 --> 00:15:29,414
So everybody at your home
has a private IP address.

319
00:15:29,414 --> 00:15:31,830
They can't connect to the
internet, or the internet rather

320
00:15:31,830 --> 00:15:34,870
can't speak to them, through
that private address.

321
00:15:34,870 --> 00:15:37,656
They can only speak to them
through the address in the router.

322
00:15:37,656 --> 00:15:39,530
And it's the router's
job to take information

323
00:15:39,530 --> 00:15:42,900
that you're sending the router
and direct it to the correct place

324
00:15:42,900 --> 00:15:46,890
and for information that's coming
into the router for the router

325
00:15:46,890 --> 00:15:48,860
to send it to you.

326
00:15:48,860 --> 00:15:52,470
>> So the routers are really the
devices here-- particularly a router

327
00:15:52,470 --> 00:15:59,010
in your home, the most common sort
of usage case for most people--

328
00:15:59,010 --> 00:16:00,870
that has the public IP address.

329
00:16:00,870 --> 00:16:03,910
That's the device that's
connected to the internet.

330
00:16:03,910 --> 00:16:07,190
And you connect to the router
to have information flow

331
00:16:07,190 --> 00:16:09,910
through it on your behalf.

332
00:16:09,910 --> 00:16:14,420
>> As I said, a modern home network, the
router and switch and access point

333
00:16:14,420 --> 00:16:16,420
are all kind of bundled
up into a single device.

334
00:16:16,420 --> 00:16:19,240
Sometimes a modem is
bundled in there as well.

335
00:16:19,240 --> 00:16:20,800
That's usually just called a router.

336
00:16:20,800 --> 00:16:23,210
But it's really all of
those things together.

337
00:16:23,210 --> 00:16:27,870
>> Large scale business networks or
so-called Wide Area Networks, WANS,

338
00:16:27,870 --> 00:16:29,570
actually keep these devices separate.

339
00:16:29,570 --> 00:16:30,470
They have a switch.

340
00:16:30,470 --> 00:16:31,550
They have routers.

341
00:16:31,550 --> 00:16:33,510
They have multiple access points.

342
00:16:33,510 --> 00:16:36,250
>> For example, at a
university you'll see things

343
00:16:36,250 --> 00:16:40,300
that look like so-called routers
mounted are all around campus.

344
00:16:40,300 --> 00:16:44,120
Those are all access points that flow
into routers, switches, et cetera,

345
00:16:44,120 --> 00:16:45,250
to pass information along.

346
00:16:45,250 --> 00:16:49,120
Because these networks are so
big that one single access point

347
00:16:49,120 --> 00:16:51,870
can't cover its large area.

348
00:16:51,870 --> 00:16:54,990
>> And so these large networks,
business networks, et cetera,

349
00:16:54,990 --> 00:16:57,710
split these into separate
devices, so the network and scale

350
00:16:57,710 --> 00:16:59,780
and grow if needed.

351
00:16:59,780 --> 00:17:04,180
So again, somewhere between us and
the internet, we have an access point.

352
00:17:04,180 --> 00:17:05,430
And that's what we connect to.

353
00:17:05,430 --> 00:17:08,992
And through there, we
can get to the internet.

354
00:17:08,992 --> 00:17:10,700
As I said at the
beginning of this video,

355
00:17:10,700 --> 00:17:12,540
this is not a course on networking.

356
00:17:12,540 --> 00:17:13,990
So this is not the entire story.

357
00:17:13,990 --> 00:17:15,109
And I've kind of glossed over it.

358
00:17:15,109 --> 00:17:17,150
And maybe I've left you
even a little bit confused

359
00:17:17,150 --> 00:17:18,670
as to what some of these things are.

360
00:17:18,670 --> 00:17:19,329
But that's OK.

361
00:17:19,329 --> 00:17:20,599
>> We don't need the whole story.

362
00:17:20,599 --> 00:17:25,250
It's enough for us to know moving
forward just basically a little bit

363
00:17:25,250 --> 00:17:27,450
about how the internet works.

364
00:17:27,450 --> 00:17:30,670
So what we know is we have these
private networks at our house.

365
00:17:30,670 --> 00:17:32,880
>> And we connect to a router.

366
00:17:32,880 --> 00:17:36,674
And that router is connected
to the internet at large.

367
00:17:36,674 --> 00:17:38,090
But what is the internet at large?

368
00:17:38,090 --> 00:17:39,930
I keep saying this, but what is it?

369
00:17:39,930 --> 00:17:43,610
>> Well, it's really just all these
individual networks at my house,

370
00:17:43,610 --> 00:17:47,460
and at your house, and at every other
house, that are connected together.

371
00:17:47,460 --> 00:17:52,030
It's an interconnected
network, an inter-net.

372
00:17:52,030 --> 00:17:53,840
So instead of thinking
about the internet

373
00:17:53,840 --> 00:17:59,080
as this giant cloud, this ethereal
thing that exists out there,

374
00:17:59,080 --> 00:18:02,470
it's really just a connection
among all of these networks.

375
00:18:02,470 --> 00:18:03,500
>> So here we go.

376
00:18:03,500 --> 00:18:04,752
We have our local network.

377
00:18:04,752 --> 00:18:07,210
And we're not the only person
probably on our local network

378
00:18:07,210 --> 00:18:08,335
trying to use the internet.

379
00:18:08,335 --> 00:18:10,940
There's probably several
of us trying to get in.

380
00:18:10,940 --> 00:18:13,870
>> And we're not the only network
that exists in the world, right?

381
00:18:13,870 --> 00:18:18,300
There are other networks, too, that
are trying to connect to the internet.

382
00:18:18,300 --> 00:18:21,400
But the internet is not,
again, a separate entity.

383
00:18:21,400 --> 00:18:25,592
>> It's just a set of rules that allow
these networks, these small networks,

384
00:18:25,592 --> 00:18:27,300
the blue, the purple,
and the red network

385
00:18:27,300 --> 00:18:28,980
here, to communicate with each other.

386
00:18:28,980 --> 00:18:31,230
So there's no thing
they're all connecting to.

387
00:18:31,230 --> 00:18:35,010
They're all just connected
to each other, right?

388
00:18:35,010 --> 00:18:37,710
>> And so somewhere on these
networks exists the services

389
00:18:37,710 --> 00:18:39,095
that we actually want.

390
00:18:39,095 --> 00:18:41,220
So maybe in the blue network
is where Google lives.

391
00:18:41,220 --> 00:18:43,303
And in the purple network
is where Facebook lives.

392
00:18:43,303 --> 00:18:46,310
And in the red network, well, maybe
that's where all those cats are.

393
00:18:46,310 --> 00:18:49,440
>> And so if we want to get
information about cats,

394
00:18:49,440 --> 00:18:55,166
we just traverse this chain of networks
to get the information we want.

395
00:18:55,166 --> 00:18:57,040
And here, I've represented
the network as all

396
00:18:57,040 --> 00:18:58,414
being able to talk to each other.

397
00:18:58,414 --> 00:19:00,300
And we can only talk to the network.

398
00:19:00,300 --> 00:19:01,910
But the network can't talk back to us.

399
00:19:01,910 --> 00:19:03,326
>> But that's not true either, right?

400
00:19:03,326 --> 00:19:04,610
This is all a two-way street.

401
00:19:04,610 --> 00:19:07,860
Information can flow through
networks back and forth.

402
00:19:07,860 --> 00:19:09,007
>> How does it do that?

403
00:19:09,007 --> 00:19:11,090
Well, the internet's really
a system of protocols.

404
00:19:11,090 --> 00:19:11,970
And we're going to
start talking about what

405
00:19:11,970 --> 00:19:14,130
those protocols are in future videos.

406
00:19:14,130 --> 00:19:16,940
>> But again, the internet
is not a separate thing.

407
00:19:16,940 --> 00:19:20,760
It's a set of rules that defines
how networks communicate,

408
00:19:20,760 --> 00:19:23,410
these small networks, these
local network that we're used to,

409
00:19:23,410 --> 00:19:26,600
the people in our house, the people
at our school, the people at our job,

410
00:19:26,600 --> 00:19:29,160
all sharing a network.

411
00:19:29,160 --> 00:19:31,900
And how these networks interconnect
and talk to each other,

412
00:19:31,900 --> 00:19:34,160
that's actually what the
internet's all about.

413
00:19:34,160 --> 00:19:36,090
So let's, in a future
video, talk about some

414
00:19:36,090 --> 00:19:38,940
of the protocols that comprise
the internet to hopefully

415
00:19:38,940 --> 00:19:42,320
give you a bit more of a
well-rounded understanding.

416
00:19:42,320 --> 00:19:43,320
I'm Doug Lloyd.

417
00:19:43,320 --> 00:19:45,260
This is CS50.

418
00:19:45,260 --> 00:19:47,351