Transcript for:
اصول شبکه و مدل‌های ارتباطی

this is episode three of my free ccna course and a huge shout out to boson software the official sponsor of the ccna course they are the reason this can be made available for free so i highly encourage you to go check them out they have the absolute best ccna ccnp labs and practice exams okay i need you to stop and think about this for a second i want you to appreciate the fact that this device right here of raspberry pi can connect to a network and talk to my iphone they can share photos they can email each other do whatever it might not seem amazing because this kind of stuff is just commonplace is what we're used to every day but once upon a time a long time ago in a galaxy far far away if you had a device that was made by two different companies they could not talk this is where things like the tcp ip model or the osi model networking models save the day like for real but how let's take a look back in history real quick a long time ago i'm talking stone ages 1960s some smart guys are sitting around their computers and they're thinking man g wilkers i really wish they could talk to each other i wish i could share a file with you friend but they couldn't but then they hatched an idea they came up with something they go what if what if we can network these things together what if we can connect our computers together and we could send data across they did that 1969 the birth of the first network we called this or they called this arpanet the usdod or the department of defense came up with it and it was revolutionary like people could actually have their computers talk to each other which i know sounds like not a big deal right now but back then that was that was it that was the new thing but hold on here's the problem though this was more of an idea like they they legit did it like here's the first like network diagram i think there ever was check this out look at that thing i have no idea what's happening and when i say idea they were like yeah this is a cool thing we can do they actually invented what's called packet switching which is what we do today but what they didn't have yet is the how how do we make these computers talk to each other you see that part wasn't quite ironed out but the idea the idea spread like wildfire so companies like ibm they were like heck yeah we have computers let's design our own network and they did it was proprietary meaning it only worked with their stuff which is fine if you have an ibm computer but there wasn't just ibm there were other companies and guess what these other companies did they also designed their own networks and i'm sorry let me step back when i say design i mean they like invented their own networks they came up with the idea of how to actually connect computers together and because these networks were proprietary they couldn't really play well with others meaning these networks could not communicate you couldn't have this device talk with this device they were basically speaking different languages this network over here is like bonjour and this network over here was like what no idea now i want to hammer this home because this is some primitive stuff i'm talking like this is before ethernet cables were invented like we're so used to ethernet cables we're so used to the ethernet ports these weren't a thing each of these companies had different versions of whatever they called theirs like you ever try to charge your iphone with an android charging cable it doesn't work it's just not compatible that was the networks of yesteryear or long time ago now eventually they realized hey this is kind of stupid maybe we should all use the same networking stuff yeah let's do that no easier said than done this involved meetings and committees and i want to do this i don't want to do that you're wrong sir a lot of that kind of stuff now there's a long and maybe interesting history if you're into that of how this all came about but we eventually ended up with a networking model a model that defines how we can connect our stuff so that when ibm makes a computer when apple makes a computer when microsoft makes a computer we're all putting the same technology inside that computer to make it talk to the other computers that's why such a beautiful thing that a microsoft computer can send a photo to an apple computer we're all using the same networking technology we're using the same networking standards now actually honestly we ended up with two models one that we actually used and then one that we still cling on to and talk about all the time i'll show you the model we use today is called tcp ip this is what every computer supports and has implemented into their system the tcp model and they also call the tcp ip stack now the other model he wanted to be the one that won so badly people were on his side they were campaigning but he just did not win tcpip won for a variety of reasons but it's just more widely adopted so then why am i still talking about him of tcp ip1 i'll show you it's weird now again tcpip is a just a list of rules or guidelines standards on how computers can communicate how we design those systems and there's a lot that goes into that so to make things more simple more digestible easier to understand and implement we divided all those functions into layers layers like this right here each of these layers defines some kind of protocol or standard we'll use when computers connect so for example the physical layer we know that's going to involve ethernet cables the network layer all about ip addresses and routers so with this standard we all agreed we're going to use ip addresses when we communicate over the internet before that standard that wasn't really the rule you could have done anything you could have used names from star wars or something i don't know transport we got tcp udp port numbers we'll talk more about that later and then application like hey when i open up my web browser and i go to netflix.com what protocol am i going to use do we all agree to use the same protocol we all agreed to use the same stuff and it's beautiful now we can all talk together we can all network together now this is the traditional view of the tcp model the layers we see here if you're studying for the ccna the 200-301 you might see the physical layer divided into two separate layers like this which i happen to love and if you watched my last two videos in the series you're already familiar with the first three layers here you've already seen them in action going through a network we get our physical the the ethernet cables the network cards the electricity flying that's our layer one and then we talked about our data link layer this is where our mac addresses come in our layer two addresses how host on the same network can communicate and the switch uses those layer two addresses those mac addresses to know where to send information and then of course we have our layer three our network layer we know this to be ip addresses we know that we assign our devices ip addresses and this is how they communicate this is how the router can know where to find people and route those packets to the right people and then we have our other layers and we will talk about those but not right now we'll get to it okay now what about the osi model where does this guy come in well let me show you similar to tcp he works on layers in fact he shares the same layers as the tcpip model he just has a few extra so physical data link and network transport yeah yeah let's talk that that's the same but then at the application layer it's a bit different we're going to add a couple more we're going to add a session layer and a presentation layer let me scoot this guy up a bit there we go now as you're studying networking as a network engineer the main difference between the tcpip model and the osi model are these two extra layers now the concept of these layers what they bring to the table do not go away with the tcp ip model i'm saying it too much all that happened is we stuffed those two layers inside the application layer but chuck you still haven't told us why we're talking about the osi model why are we even talking about it this is why i told you these two models were at war with each other who was going to win and during those wars it was widely believed that the osi model was going to be the one that was adopted which by the way stands for open systems interconnect and because it was thought to be the clear winner we started using the layers that the osi model has as our day-to-day terminology and even when tcpip was the clear winner and it killed and murdered osi we still refer to the osi layers when we describe network functions now again not a huge deal because layer one two three and four are the stinkin same as the tcp model as long as you're referring to the cisco version of it right now but when you get up to the layer five layer six and layer seven clearly we got a little disconnect there but when network engineers talk about it osi always wins we will always always always refer to the application layer as layer 7. this right here is layer 7 and there's only five layers here that's just how we do it it's how we roll but i will say this if you're trying to learn networking if you're studying for the ccna you need to know both of these models there's a fun way to memorize this so the osi model seven layers harder to memorize uh we'll use a mnemonic device so application presentation session transport never get a link physical uh let's try all people seem to need data processing i'm sure there are better ones that's just how i learned it let me know below if you have a better one i can't tell you how many times throughout my career i've referred to that phrase that mnemonic device to remember the seven layers and then what about reverse what if you're gone not going from application to physical or if you're going from physical to application which can happen routinely right i got one for that too please do not throw sausage pizza away makes me hungry every time now again a big reason to remember and memorize the osi model is a you need to know it for any exam you might be studying for and b it's honestly the thing we reference the most when network engineers are troubleshooting or working through any kind of networking issue oh that's a layer 7 issue application hands off not my problem or hey that's a layer 1 layer 2 layer 3 or layer 4 issue okay time to see what you learned get your copy ready your thinking cap on let's do this exam questions right now question number one which of the following operates primarily at layer two of the osi model select the best answer and go if you said the answer was switch you're absolutely right if i hit show answer fingers crossed yes i'm right the switch operates at the data link layer layer 2 of the osi model router where's the router operator layer three ip addresses the network layer the hub that might have been a little bit confusing for you because we compared switches and hubs in one of our earlier videos in the series where do they operate remember hubs are stupid they got no smarts they don't operate at layer two they're not even aware of mac addresses all they do is just repeat electrical signals when they receive them out all ports so they are primarily physical and quiz what layer is physical layer one right and then a wap a wireless access point this was kind of a tricky one because they do operate at layer two they also operate at layer one so that primarily focused on layer two so if you put that answer you're half right you're kind of right but we're looking for what primarily operates at layer two and that of course is a switch question number two which of the following devices operate primarily at the physical layer of the osi model select two choices now we kind of already covered this let's see what you got go okay here we go here are the answers a repeaters and c hubs let's see if i got it right boom now this may have been a bit tricky for you because we haven't talked about bridges and that's fine but through the process of elimination we know that hey switches those are layer two we just talked about that routers layer three of course we just said that hubs are physical and i even mentioned that hubs will repeat electrical signals when they receive the electrical signals over the wire and repeaters do the same thing bridges on the other hand are similar to switches and that they do deal with layer 2. [Music] but guys that's about it if you like this video hit that like button if you have any comments or questions or need help with your ccna comment below or you can jump into my discord server ton of guys in there a ton of gals in there helping people out now if you want to see more of this more stuff like this go check out this is it.io it's a membership that david bomble and i run go check it out it's pretty cool and also in just a few hours i'm launching episode four of this series where i dive deeper into the osi model and the tcp model and actually watch a packet go through a network and we'll analyze each layer as we hit it so if you're looking for that it already might be out actually so check it out anyways episode three that's a wrap i'll catch you guys later [Music]