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All right.

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So this whole time we've been talking we've been talking about networking and I've been throwing terms

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at you and I every time I throw a term at you I try to use the respective layer for it.

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So you've heard me say layer to layer three layer four.

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And those all correspond with what is called the ISI model.

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Now if you're ever in a network interview or if you're ever talking to somebody who has experience in

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networking or even if you're on the Help Desk taking tickets knowing the ISI model is incredibly helpful.

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And people will just throw layers at you especially the people who have been in the field for quite

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some time might just say layer two instead of a switch or they might say layer three instead of a router.

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So I'm going to discuss the ISI model really quickly give you a pneumonic on how to remember it and

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just talk about some of the concepts within it and how to troubleshoot down it as well.

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So I pick this up from Keith Barker a long time ago great trainer by the way.

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And this is the mnemonic.

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SO WE'RE GOING TO GO P. D and T S P A and this stands in my head for.

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Please do not throw sausage pizza away again that is please do not throw sausage pizza away.

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So I'm going to put numbers corresponding to the layers in front of it here and we're gonna go ahead

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and type these out one by one.

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So on the first layer here we've got what is called the physical layer and you can think of your physical

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layer as like a data cables or like your cat six cables.

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Stuff like that something you might you might plug in.

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Right.

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That is the physical layer.

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And we've already talked about layer to quite a bit Layer two is the data layer and that is our switching

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right.

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And also our mac addresses going down the list.

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We've got the network layer which is IP addresses also routing the fourth layer is the transport layer

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which is DCP UDP which we have talked about as well.

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And the last few.

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So the session layer we've got the session layer which is just session management.

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You don't really have to worry too much about this one.

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Six is the presentation layer.

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Now this should be familiar to you because think about WNBA j peg movie files.

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That's what your presentation layer and so media.

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And then lastly we've got the application layer which is like a DP S.M. T.P. your applications that

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you utilize.

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Right.

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So we've got this laid out here.

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And you might be asking why is this important.

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Well again when we say something like my home router is a layer two three.

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So that means it does it does switching and it does routing.

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Right.

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You might think of this in another way as well you might be asked to troubleshoot and something to talk

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about too with the with the RSI model is when we receive data we receive data down this physical layer

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all the way down to the application when we transmit data.

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It goes out the application layer down to the physical when we're troubleshooting this.

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It is always best to start with a physical and go down to the application level.

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OK.

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So say you get a you're working help desk and you get a phone call and somebody says you know my Internet's

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not working helped me.

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Well what's the first thing you're gonna do or you're gonna ask them application level questions.

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Yeah.

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Probably not.

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You might say hey can you look at the back of the computer.

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Do you see a cable plugged in.

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Oh the cables plugged in.

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OK well do you do you see the where the cables plugged in.

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Is there a blinking light is that blinking like green.

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By chance OK we're checking the Nick right.

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And then we might ask them to you know do they have an IP address what's going on all the way down.

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And then we travel issue all the way down to layer 7.

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So we wouldn't start to layer seven right.

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We would start from the basics and moved down.

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So it's important to know this.

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This isn't a help desk course by any means but it's super important to notice especially if it's been

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a while since you've seen this network stuff or even if this is new to you that the OSA model is commonly

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referred to even as a pen tester.

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I get all kinds of layer to layer 3 talk and you will be sitting in meetings with network engineers

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with people who are very very smart about this stuff and they're gonna throw all this lingo at you.

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So if you know this lingo really really benefits you or else you're just going to sit there and wonder

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what the heck they're talking about.

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So hopefully this is a quick informative method for you.

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And again remember please do not throw sausage pizza away.

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That's the easiest way I remember it.

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You can make up your own harmonics if you want.

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People of other things as well if you've got a do you got a favorite pneumonic please feel free to comment

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down below and tell me your pneumonic as well so I'd love to hear some of these other ones.

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So let's go ahead and move on into subletting and then we'll we'll start moving into other fun parts

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of the course.