Hey, everybody.

Welcome to the next video.

So in this video, we are going to be going over the OSI model.

Now the OSI or Open Systems Intercommunication Model is commonly used to identify the flow of communications between two devices.

So this is everything from you going to Google.com or redteamnation.com and hitting enter all the way down to where the data gets sent and back.

This is commonly used for troubleshooting.

However, some people refer to things as a layer two or three switch, which we'll talk about in a little bit.

But outside of that, from a red team's perspective, it's not as important of information to know.

But I want you to understand and be aware of what it is and what it looks like and what the components are.

Just so you have that extra little bit of knowledge when somebody refers to a layer three switch as an example.

Now, the model consists of seven layers.

So from top starting at the highest number to the to the bottom with the lowest.

So first is application layer, then presentation, session, transport, network, data link and physical.

Now the first one is the application layer.

So this is closest to the end user, which is what you're normally going to see.

This is how this is the software itself that interacts.

So let's say the the browser wants to go to redteamnation.com, in that case, high level APIs, that it's interacting with the browser itself to be able to start the process of transferring the data.

So this is this is the application layer after layer seven.

Now, Presentation Layer.

This is where the protocol starts to take over, where if it needs to be encoded into a specific way or it needs to be compressed or encrypted or decrypted, this is where the layer where all of that type of process happens.

Now, the reverse happens when you send the data across the network and it goes back up from layer one to layer six, which is the presentation layer.

It's going to unencode or decompress or decrypt whatever the data was.

Now, next layer is the Session Layer.

So this is starting to get more into the protocol on how the protocol itself is being used.

So it could be TCP, IP, it could be TLS thats on top of that or SSL.

It makes sure that all of the sessions between the two devices are in sync so it knows what was sent, what wasn't.

It also knows whether there's something active or not.

So the sessions hasn't been used in a while and it can kill off the session.

Next layer is the Transport Layer.

Now this layer handles the actual transferring of data, the segmentation of packets to making sure that they because the packet can only hold so much data.

So what you want to do is you want to segment that a little bit further into 5, 10, 20 or 100 different packets that all get sent across.

So this is where that layer tends to happen.

And the acknowledgments that we receive, the data happens at the transport layer.

Next layer is the Networking Layer.

So the networking layer manages the IP's, the routing and the IP layer of the packets.

So the IP header.

Now, this is an important layer because this is how things get from one set to another.

The Data Link Layer.

So this handles the data frames.

So there's something called in most cases you're going to be looking at something called an Ethernet frame.

Now, an Ethernet frame is the top most level of a packet or the type of frame.

So in this case, for example, wireless will have beacon frames.

So the frame is what, the physical medium or the wires, the fiber, whatever the case might be, is able to transmit it under the the core circuitry understands what that frame looks like so it can start transferring the data.

So an Ethernet frame can only travel over an Ethernet based cable, which is the twisted, twisted pair.

So it's important to understand that.

Go ahead and look a little bit more into data frames or Ethernet frames just so you can kind of get a better understanding.

This layer also corrects any errors that that happened during transfer.

So if something's out of sequence, we haven't acknowledged something.

Any errors in transit occur here.

And this is also, again, the protocol.

This defines the protocol used to actually transfer the data itself at the lowest level.

Now we have the Physical Layer.

The physical layer is the where the wire sits, the radio waves, the wireless, all of that.

It sits at this layer. This is the lowest layer you're going to get to.

This is where the the signals themselves, the on-off gets sent across the network medium.

This is that's all that's really important about this layers, that it's the actual physical hardware sending raw signals out.

Now, this is a high level over the OSI, the OSI model, it's it's important to understand the model and what that it exists and sort of what the layers are.

Now, we don't have to go into every detail and you're not going to have to know this off the top of your head.

But it's good information to just keep in the back of your mind whenever it might present itself.