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If you watched our internet primer video, I left a bit of a cliffhanger,

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right by talking about the internet and how it's a system of protocols.

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Well,

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let's talk about the first of those

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protocols that actually comprises the internet.

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And interestingly enough, it's called the internet protocol,

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which we usually refer to as IP.

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So the internet, as I said is an interconnected network and internet,

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which is really just several networks woven together

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and agreeing somehow to communicate with one another.

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What is this somehow I'm talking about? Well, this is the internet protocol.

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This dictates

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how information

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is transmitted from point A to point B and this is sort of a condition of joining

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the network of the internet

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uh is agreeing to follow this protocol when information needs

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to be moved from point A to point B.

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So at the very end of that internet primer video,

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I showed this image of what the internet was.

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And on a small scale, this is actually probably pretty accurate,

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this might be how three networks actually talk to each other.

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But it's a bit misleading. And the reason it's a bit misleading

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is because if I just number,

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the networks for the sake of convenience here and we get

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rid of everything else and just focus on the networks.

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It's a bit misleading because it implies that all

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three networks have a connection to one another.

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One is connected to 22, is connected to three and three is connected to one.

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And when I talk about a connection here,

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I'm talking about a physical wired connection.

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We do have wireless,

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but it's really impractical for data to

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be transmitted wirelessly over a large scale.

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And so at some point, we really do rely on wired technology,

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telephone wires, fiber optic wires,

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various technologies that are physically connecting point A to

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point B and on a small scale like this,

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this might be accurate.

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But as this, as the image gets a little bigger,

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let's now imagine we have six different networks.

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If that's true.

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Now we have something like this for every

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network to be connected to every other network.

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And if you look, every, every network has five arrows connected to it.

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So everything is connected to every other network.

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But we only have six networks here and already look at how much wiring

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we have to employ,

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right? And the internet consists of a lot more than six networks.

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We can't afford to wire each network to each other network,

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especially considering some of these networks span oceans,

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right?

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If we're trying to connect to a network in Asia or in Europe,

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we're gonna have to span an entire ocean

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if we need to.

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We, we're gonna need to use wires at some point,

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but we wanna minimize the number of wires we actually

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use.

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We don't wanna send a million wires across the ocean

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because they cost millions of dollars a piece to lie down

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and so

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rapidly, we wouldn't be able to afford the internet anymore.

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So we have to have another way for every network to talk to every other network.

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Or else we have pieces that are of the internet

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that are disconnected from other pieces of the internet.

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And that's, that's not what we want,

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but we don't want to have them all wired together.

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And this is where routers come back into play.

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We can use routers in the following way.

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What if instead of every network being

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physically connected to every other network,

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we had these intermediary pieces where the

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networks were connected to these intermediaries,

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which were connected to a few networks.

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So instead of having one connect to 2345 and six,

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maybe one connects to a router which maybe connects to one or two of those networks,

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but also maybe connects to other routers,

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which also will connect to those other networks.

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And the with the router's job is it contains information called a routing table

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that dictates. Where do I go? If I see a particular IP address?

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If I see an IP address starting with four, I'm gonna go this way

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if I see an IP address starting with a 12, I'm gonna go.

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That way,

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we don't need to be connected physically to

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network number four or network number 12. In this example,

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we just know generally where we wanna go. And if you think about it,

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this is sort of similar to the concept of recursion that we talked about.

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Uh when we were talking about it in C

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I'm not gonna connect you

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to exactly where you wanna go. I'm just gonna move you one step closer

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to where you wanna go.

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And I'll let somebody else deal with solving the rest of the problem.

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I'll just solve this little piece of the problem

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and defer the rest of it to somebody else.

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So routing information is actually kind of similar to

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recursion if that's a concept that you understand,

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well, maybe that analogy would help.

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So let's take a look, look at this networking example again and assume that

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um again, we're gonna use those same six networks one through six.

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So let's just say that every IP address on network one starts with one dot something.

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And we'll say that there's, you know, some,

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some other thing that deals with how to all

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the systems that are connected to network one,

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we just care about connecting all of those networks together in an internet.

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So every

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device that is connected to network one has an IP address

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that starts with one dot And then three other numbers.

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This is a generalization of the way things actually work. Um It's

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quite a bit more precise than this,

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but this should give you a general idea

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of what the internet protocol is actually doing.

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So this was the diagram we had before, this was the system that was not sustainable.

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Even six, this might be OK.

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But if we get to 10 or 20 or 50 we're gonna be lying a

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lot of wires and 50 is still also not even the tip of the iceberg

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uh as to the number of networks we have.

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So this, this model is unsustainable, we can't stick with this.

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So let's instead

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adopt this model where we get rid of all the wires between the networks

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and we add

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routers.

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So these yellow boxes represent routers and

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their job is to move information generally closer

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to where it's supposed to go.

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And maybe these are the connections that these networks have and

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maybe these are the tables that are built into the router.

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So if we just start by looking at

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network one, for example,

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basically what it says is if I ever see an address that doesn't start with a one,

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that's what the exclamation 0.1 or the bang one there, not one,

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I'm going to pass it off to a router

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and from there, the router can make a decision.

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The router says, if I see a one, I'm gonna move to network number one,

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that's the green arrow heading to the left out of that top left box.

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If I see a two,

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that's the arrow sort of heading to the top right towards the purple network.

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If I see an IP address starting with a two,

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I'm gonna go towards the two network.

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If I see a three, a four, a five or six,

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that's that red arrow coming out of the top left router.

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I'm not connected to 345 or six,

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but I know somebody who is or who's a little bit closer to there.

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So I'm just gonna say every time I see an IP address starting with 345 or six,

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I'm just gonna send it to that router, so I'll move it,

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I'll move it a little closer to where it's supposed

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to go and let that router deal with the problem.

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And as you can see

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if you wanted to pause here and trace, you can get to every other point in the network.

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Um, from wherever you are,

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all six networks can still connect to every other network,

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but they're not physically connected anymore.

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There are now these intermediate steps.

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Now, of course, there's a trade off of speed, right?

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If one was directly connected to six,

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we wouldn't have to go through two routers along the way.

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So we'll be able to get the connection a little bit faster,

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but maybe that trade off is worth it, right.

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If it's gonna be so expensive in terms of actual cost

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dollars and cents to

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physically wire all these networks together,

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maybe a little bit of slow down and speed is OK, we can tolerate that.

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So again, in that example,

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we were just talking about on none of the networks

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were directly directly connected to each other at all.

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There could have been maybe in that example,

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we could have made it so that maybe network one

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and two were directly connected and that would be OK.

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Some networks are physically connected to other networks,

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but they're not all connected to each other.

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They rely on the routers in this particular example,

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to distribute the communication from point A to point B

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on a small scale.

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Like what we're talking about here,

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this configuration actually might be more

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inefficient than just having direct connections.

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But on a large scale, we can,

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we can scale the system a lot better.

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Um It's really gonna reduce our cost

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of network infrastructure to have intermediary routers.

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Uh whose job it is to move traffic from the

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center to the receiver from point A to point B

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um as opposed to wiring everybody together.

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So let's take a look at an example

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of information traveling using this internet protocol.

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Let's say that I am

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um I am physically located at IP 1.208 0.12 0.37.

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So I exist somewhere on the one network

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and I want to send a message to you and you're on the five network at 5.1 88.109 0.14

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your IP address specifically doesn't matter.

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But in this particular example, we're talking about this generalization

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of what the internet protocol is all about.

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You're on the five network and I'm on the one network.

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And as you can see, we're not connected to each other at all.

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So I start out

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and I wanna send you a message.

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And so somehow I communicate that message to the router.

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The router is the one that actually has the IP address.

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And it's looking at where it's supposed to go. We're going to five dot something.

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So now I'm gonna start using my or the router rather,

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it's gonna start using its router table to pass information along.

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It sees that five is not one. So it's because I'm gonna pass it to this guy.

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Then this guy has to make a decision. Where am I gonna go? Well, it's not a one.

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So I'm not gonna move to the one network and it's not a two.

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I'm not gonna move to the two network. It starts with a five.

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I'm not connected to five, this router says, and so I'm just gonna pass it off to,

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I'm gonna go down this path.

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This is where threes and fours and fives and sixes go

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and I'll let that guy deal with it.

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I'll get it a little closer to where it's supposed to go.

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I know, it's supposed to go in that general direction,

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but maybe that guy can deal with it.

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Ok.

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So that guy looks, he says, ok, this IP address starts with a five.

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Well, I'm connected to three and to six.

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So I can't get the message directly where it needs to go.

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But that other router over there, I know if I send it fours and fives,

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it can handle those.

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So it passes it along down the path.

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And then this router says, well, I'm connected to networks four and five.

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So yes, I can help you. I'll take the IP address.

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Also the five, I'll give it to the five network.

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The five network will do some work on its end and give the message to you.

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And now we've successfully transmitted a message from me

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to you using the internet protocol again, very generalized

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for purposes of illustration as to what's happening.

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But that's pretty much how the internet protocol works.

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The routers know generally where to send it

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and will send it one step along the way,

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getting it closer and closer to its destination

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until one router is physically connected to the network or the address or whatever,

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whatever

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in question and gives it there.

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Now

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in general, except for really, really small small messages.

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Um

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If it's not gonna send it as one big chunk of data, right?

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If I'm sending you an email, a very long email,

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say it's not gonna take that entire email, bundle it up in,

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you know, a ball or a package or whatever

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and send that entire thing down the network.

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First of all, sending information along the network is expensive. It does add up

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and the larger the chunk, the more costly it is to move every step of the way.

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Um And if it, if there's somehow a slowdown and there's this giant,

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sort of like if you're driving on the

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highway and there's this giant truck kind of blocking

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the way and you can't get around it on either lane because it's kind of spread out.

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It slows everybody else down behind it.

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But small cars, if they were all small cars, they might be able to

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move around. That analogy sort of helps a little bit.

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So one big block in the system can really slow everybody else down.

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And so what IP is going to do is split this data into packets. It's gonna take this big

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email or FTP transfer or file transfer or maybe I'm making a request

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to a web browser because I want a picture of a cat.

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Um And it's gonna take that request or that email or that file and

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break it up into many pieces and send all of the pieces separately.

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So, in fact, I'm filling the highway with a lot of small cars which can all move

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instead of a big truck that might, if something goes wrong,

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um,

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throttle the traffic for everybody else,

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another side effect of this is if there's some sort of catastrophic failure

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and a piece and, um, and, you know, something goes wrong and the packet gets dropped,

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something is failed and the message can't be communicated the net with the router.

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Maybe had too much stuff going in. It couldn't juggle everything.

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And so it just literally dropped it. That's sort of the analogy. Right.

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It has to, it's got a lot of things going on. It's passing information from

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point A to point B. We're not the only two people on the internet.

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So it's has to process a lot of traffic

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and if it doesn't have enough hands and it can't figure out what it's doing,

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it might just drop something

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so it can do something else. It's got too much going on

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if we had our messages one huge block and that was what got dropped.

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Now, we have to send the message again

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and we are now possibly causing traffic again and we were

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on the risk of that huge block being dropped again.

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But if the data has been broken up into packets and we drop one of those,

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it's a lot less costly to send that packet one more

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time as opposed to the entire thing one more time.

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So IP is responsible for

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getting information from point A to point B

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and also breaking the information into small pieces

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so that the network isn't overly taxed.

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IP is also known as a connection, less protocol,

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there is not necessarily a defined path from

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the sender to the receiver or vice versa.

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Now, in this example,

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we've talked about there actually is only one way to get to every network.

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Um So in this particular illustration,

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there actually is a defined path from point A to point B.

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But we can change that by just making one modification to the two

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routers on the left by adding this condition to the router tables.

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Now notice that from the top left router,

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there are actually two ways to deal with a four or a five IP address.

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It can go down to the lower left router

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or it can go to the right to the right router. It has multiple options

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and this is actually kind of a good thing, right?

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Because it makes our network more responsive if for example, it's sort of like a gps

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if you've ever been driving on the highway

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and suddenly your gps warns you that traffic is ahead,

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that's you, you want to avoid it if you can. And so you can recalculate your route

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and

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the, the router tables.

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In addition to uh having information or the router network rather,

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in addition to having information about

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uh where

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packets should go or where data should go.

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There's also sort of this general pulse on the state of

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its local network where what's gonna happen if I send it

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uh down this path versus this path.

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And so

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in,

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in light of

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heavy traffic situations on the network,

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maybe things will get routed a more inefficient

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way or a more generally inefficient way.

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Because if we go the regular way, there's gonna be a lot of traffic,

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the highway is completely jammed.

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So maybe what we'll do is instead take side

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roads which ordinarily would take a lot more time,

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but no one's really using those side roads.

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And so we can route our packets that way.

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So not every packet of a big chunk of data might

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take the same path from the beginning to the end.

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And our network becomes a lot more responsive.

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If our router tables allow for there to be multiple options

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um for where to go.

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We don't,

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we're not depending on that one truck moving out of the way we can

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get off the highway at the next exit and take a different path.

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And so

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the internet protocol sort of does a little bit of that

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too.

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So that's the basics of the internet protocol.

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Um

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But there's one more issue to deal with, which is what happens if we do drop a packet,

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how do we know we're gonna send that packet again?

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Right.

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Well, internet protocol doesn't guarantee delivery.

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We're gonna be depending on another protocol to

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deal with that called transmission control protocol TCP.

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Um And we're gonna talk about transmission control protocol in the next video,

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I'm Doug Lloyd. This is CS 50