So we've just covered the S I reference model and we talked about how it's a seven layer model that was really designed to promote interoperability among vendors, but also to help us understand the various things that have to happen in networking and allow us to focus on particular devices, particular protocols
that implement these functions.
Well, there's another model. Of course there is called the TCP I P model that's broken down into four layers and maps loosely to the OS high model. So here's how I'd look at this from a testing standpoint. If they just say at what Layer does such and such operate as a router operate,
go immediately to the S. I model
right layer three network layer, make them tell you T c p I p model. So if they just don't give you which model to use, always default back to O s. I
okay now, the TCP epi models made up of four layers and this came to us from the Department of Defense and you can see the top three layers in the S I model map to the very top layer of the TCP I P model, and that's called the application layer.
Now the session maps to actually the session in the transport map to the host to host or transport. I think that's very accurate, too, because there's a lot of overlap between the session in the transport layer of the U. S. I model. So session and transport Goto host to host.
And it's also being called the transport model as well.
Now the network layer maps to the Internet work layer or the Internet working layer,
data link and physical. The two bottom layers are either called the network access or the network interface. So what I would do,
I would know that the S I model inside out and upside down, and then I would know how the TCP I p model maps toe s I. And if this is something that you haven't worked with a lot or not really familiar with a real strong on,
I would make this something that I put in my brain dump sheet before I start the exam. So you get that scratch sheet of people
paper I would jot down the seven layers of O s I the four of TCP I p, and how they match just so I can always refer back to it. They do ask for my understanding. Is that us questions on both.
But to make sure you know this mapping
now, because I'm fabulous, I have created a chart for you. And the way this chart works is over. On the left, you have the seven layers of O s. I. And just a short snippet of what happens at each. Also, if you'll remember, we talked about the PDF or the protocol data unit.
So what do we refer to data
at the top three layers. We still call it data at layer four. We call it segment packets frames.
Excuse me. Bits all the way down to lay your one.
Ah, on the next column E we talk about what ah, basic service is or just any additional information particularly I would recommend focusing on attacks at certain layers. Like, for instance, we seethe sin flooded layer four. We see Ping flood Smurf attacks down it,
uh, layer three, then the different firewalls now talking a minute ago about colonel level firewalls versus packet filter, and we'll get more in depth in this just a little bit. But I think you'll find that helpful protocols at each of the layers
and you'll notice at Layer six, even though F S is a technology, not a protocol, and then also on the far right how it maps to the TCP happy model. This is well worth knowing. I tried to make. This is comprehensive without being too
ah, Labrador or, you know, delving off into tangents.
So I think that's a really good chart that would certainly help you with your OS I model.