This articles we're going to look at the OSI model and then the differences between TCP and UDP. These will be sea, Send articles stabbing repackaging for the new CCNA and that's because these topics have been moved over to the new CCNA. It's interesting to know that the OSI model and the tcp/ip model, And not specifically mentioned in the new seating blueprint. However, Its most likely a assumption of a prerequisite to the new CCNA. And the reason for that is because the CCNA does mention a lot about layering and it's very important as a network engineer, To actually understand how the layers work and when someone says layer 3.
For you to understand how layer 3 operates with 4 and to the layers above and below, It is also important to understand the encapsulation and decapsulation process which we dive into a lot more detail later, Clip first OSI model now TCP UDP and then we'll look at Packet, Tracer and then jumping on to some physical equipment. So let's get started the CCNA journey with me, Rhine and in this article we're going to look at part 1 off the tcp/ip and OSI model. For those who don't know, You can contact me here on EveDumps, Facebook, LinkedIn and Twitter. I want to give an understanding of why these models important than what t allow us to achieve.
Now, Here's for reasons of why we actually use models. T help us break down the bigger picture to help apply standards into network and architecture. T provide easier and logical troubleshooting and t allow vendor interoperability. Now what you've got to keep in mind with these models? Is t don't actually physically exist, T're, Just a theoretical model that allows us to apply it to networking and to solve how these protocols interact with one another and fun that enable us to actually put forward these points? I put in front to you now so to keep you kind of an example of that.
Let's think about then durability. Let's say we have our OSI model and for those who don't know, The OSI model is actually seven layer model each layer having a important role in actually providing a host to better communicate with one another and we're going to get into that in a bit a Bit later in the article series, But for now let's just bear with me, While I explain a few things now, Mat lay 2 of the OSI model. This is called the data link and it's essentially where protocols like Ethernet, PPP, Hdl-c and many more run, But for now is want to be interested in Ethernet. Now we know from our previous articles that Ethernet is a protocol that runs on switches, Switches run at layer 2.
Now you can get switches that run above that, But for now this stick with the basics, So switch runs ethernet layer 2. Now, If we are, Let's say a vendor for Reuters and Reuters, Well at layer 3 and we've decided, We want to have a new product and we're going to specify we're going to specialize in switching now. What we would need to do is essentially apply the standards that are in place to ensure that our switch is capable of running Ethernet and providing we stick with those standards. What that allow us to do is ultimately achieve, Then the interoperability.
So if we build our switch to the standards layer 2, Then if we have another switch, Let's say from another manufacturer and we decide to plug that into our switch. We can be sure that the behavior for the ethernet will be fine. What this also allows us to do is not have to worry about the upper layers, So, Let's think about our route, Our you know our route her once at layer 3. If we were to plug a layer 3 device into her - and there may be another router over here - we can be sure regardless, If is our switch or another manufacturers switch, Because we followed these standards, It's kind of a form the same and also because the standards Have been followed, It allows vendor interoperability, Meaning, Let's say this is a Cisco router and over here. Maybe this is something like a a draytek, Regardless of what we use at this layer.
It will work through our layer, 2 Ethernet, Because we've built it against those standards. It also allows logical troubleshooting, So let's have a think about when you're troubleshooting there's actually a bunch of troubleshooting theories that come along with the OSI model, So there's something called the top down and the bottom up and the divide-and-conquer. Now, Let's just go through an example of that, Obviously top down would be starting at the application layer, So investigating things like HTTP and things like FTP, Whereas the bottom up would be checking out the physical cabling to begin with, Not see from network engineers. We'Re more inclined to go from the physical up, Whereas software engineers and and other sort of professions may go top-down. However, What's more common, Is you use the divide and conquer approach so to give you an example of that, Let's say we have a PC we've decided to plug that PC into our newly switch a newly built switch, And the first thing we do is try to Ping this here, Which happens to be let's, Say our default gateway on this segment now straight away.
If that was to actually work. What we've done there is: we've skipped any troubleshoot and required at layer 2 and we've divided and conquered straight up to layer 3, Because this is where IP ones, Let's say now, For example, We actually we try to tell MIT to this particular router in order to Manage it, But telnet didn't work well, That tells us is essentially anything up from layer 4, Where TCP and UDP sit and up to the session the presentation and application layer. Summing up here is causing that telnet to fail, And we can forget looking at anything with the physical with the ethernet or the IP we know from that ping and using that define and conquer approach. That is something above. Therefore, One do now is jump into the models, The history of the models, How t come about to what t are today and what models you need to be aware of in order to pass your CCENT certification, There. So there are a few models.
Initiative started with the ARPANET reference model in the 1970s, And then it moved into the widely adopted tcp/ip model, And the tcp/ip model is sometimes referred to as the DoD model, Initially start off with just four layers. As time progressed, T spit it out the bottom into two, And you can see that is using the datalink and physical, Similar to what we've just discussed in the OSI model, And this was a five layer model and then what happened is as time progressed, OSI model The open system interconnect out and there's an organization called the International Organization for Standardization, I'm actually written like this. Essentially, T came up with the open system, Interconnected model, And that was around in the 1980s. Now, There's some historic around these models, And essentially some of the things to remember is these here are sometimes referred to the upper layers and the bottom from four downwards referred to as the lower, And the reason for that is because in TCP t decided to split That up and a lot of Engineers tend to group the application.
Now the reason that group, It is because we, As network engineers, Our responsibility, Tends to stop at the transport layer long as the transport layer is receiving the correct protocols and ports from the session layer and above then we can be sure that the following layers will Will work, What we also know is is the naming convention. So here, Obviously it's called network interface and link, Whereas it was changed to datalink and physical and you'll also notice that the layer 3 is called Internet where, As t changed it to the word network, For you as part of your icnd1 via CCENT certifications. The two models that you need to be fully aware of is the update version of the tcp/ip and the open system interconnected and the differences between them as part of you exam now, A few of things to pick up on this slide, You may hear a legacy Thing back in the ARPANET reference model: t played more, T toyed around with the idea of having sub layers. So an example that, If we go back to, If we look at the OSI model, If we think of a protocol example called ARP.
The address resolution protocol for those who don't know this protocol essentially allows a host on a segment. So what I mean by that is a PC may be directly connect to another PC or maybe there's a natural switch in the middle, Essentially the same broadcast domain. If t wanted to talk to one another, T had to have some sort of resolution in order to find the IP to Mac translation. So essentially, A PC would up over quest, Essentially an ARP request out to the wire to everyone on the on the wire who actually owns this particular IP address, And for that person who owns that IP address to respond with their MAC address. So then t can build the layer 2 frame in order to send their traffic now because op interacts with IP and it also interacts with Ethernet.
Some concepts arise with saying. Maybe this particular protocol runs in between layers, I example layer 25. So you may hear engineers refer to sort of sub layers if you like, Within between other layers, That already exist, And it's not so common nowadays, I think, Essentially, The idea was with these models was, Ideally every protocol could fit into every model. However, As time progressed, It was clearly that wasn't gonna be possible, So an example of that is, If we think about a firewall, The firewall, It can block application level, Which is all in the up layers.
It can block TCP UDP, You can block IP Ethernet and has physical security, So you could argue, Firewall ones are all layers in the OSI model, So I think essentially, As time progressed and t come up with splitting out this model into numerous layers. The idea was to split it up in order to capture all the protocols, But realistically, In hindsight it's certainly not possible, So that's kind of stopped at this seven layer, But nonetheless you can very generalize almost every protocol into to each layer and in turn that helps Us with troubleshooting and applying standards to the network, The last bit I want to pick up on this slide is something I've put here called a PD, A PD. You is a protocol data unit and I'll go into this shortly, But if you ever think about something called encapsulation, If we have our data, Let's say this is our data. Essentially, As the application moves down, The stack each layer puts his own header or called apdu in front or essentially encapsulates the data.
So let's give an example, Let's think about transport. What it would do here is. It will pick what transport protocol to use and then it would pick what layer three protocol to use and then it will put a MAC address on the front of it and then it will transfer a transfer it across the wire to the actual receiving host. Essentially, This header, If you'd like and sometimes trailer in this and in layer two, It's the only one that adds the trailer, But essentially these headers are referred to as protocol date units and each protocol data unit from the session down has a unique name.
So you need to be sure that when we're thinking about layer, Four we're speaking in segments we'll think about layer, Three we're talking in packets and then we think about layer, Two, What's open in frames and the same with layer, One its bits. Sometimes I heard it called cells now to give you an example: if we think about a switch again, What you wouldn't say is: oh you're, Switching package, That's incorrect terminology, Because a packet is layer, Three . Now, If it was layer free switch, Maybe that may apply, But for now let's not go there, It's purely a layer, 2 device. Therefore, The correct terminology would be it switches frames, Because it's concerned about the layer, 2 element of the OSI model and, In turn the layer, 2 element of the OSI model is called a frame.
If you think about a hub, A hub is a dumb device. That's not aware of anything cows other than electrical signals, So you could say that this here repeats bits. You wouldn't say it repeats frames. So it's saying just to keep in consideration.
It may seem pretty pedantic in a sense, But it's certainly something you need to be aware of and will come up in some of the certifications as you move forward in your career. . So what want to do is cut a lesson a little bit short because I'm concerned with the next bit when we talk about the encapsulation and decapsulation process and go into the OSI model in more depth. We'Re going to need a full sort of 20 minutes to cover that off, And I want to cram it all into a longer article.
So, Let's recap what we've learned on this one: we let the models and what t achieve. We know that it helps to apply standard, Internet rocking art architecture and devise easier and logical troubleshoot in where to quick. Look at the models we looked at the dod model. We spoke about the ARPA reference model and the open system interconnect.
It's important to remember who created the open system into kinetic model. The International Organization for Standardization also referred to as the ISO and again that was in the 1980s, And we also finished off with understand or PDUs. So PBU is the header essentially or in some sort or in some cases the trailer that's added to the data as it traverses through the OSI model and, Like I said we'll get into that now in the next couple of articles, Explain how it actually works and What runs each layer, So you have a bit more of a solid foundation for now. I just wanted to give you a bit of an introduction to that. I hope this article has been informative.
EveDumps offers all of the necessary preparation materials with PDF and VCE files. These materials consist of CCNP 300-415 Questions, practice questions & answers and a study guide. These materials assist exam candidates in passing certification exams more quickly. The most recent questions added to the pool of questions used for the exam, practice test questions, and correct answers PDF & vce are all validated by professionals in the relevant sector.
