A Penguin Said That Nobody Drinks Pepsi

good morning everybody and welcome back to Next Door nedman you would be forgiven if you've been watching this channel for a little bit of time and had the question why is this guy calling himself the next door nedman most of what he talks about is server admin level stuff so why is it next door net admin that's a fair point most of what I've talked about on this channel so far has been server admin stuff that you would work on but I am a network engineer that's my job title and I consider myself a network admin because networking actually is my strongest suit that's that's what I do and I have a knack for but so far I haven't talked a whole lot on the networking side of things because that tends to be a little little more complicated not really I don't find it complicated honestly but that's me and I'm a network adman there's lots of numbers and math and complexity that if I'm entirely honest I haven't quite figured out how to discuss in a YouTube format mainly because I have a day job I have lots of other stuff going on and and I don't know video editing very well so I don't have the kind of ability to put up fancy graphics and illustrate things the way that I would like to except with my hands which I do use a lot that being said I thought that I would actually discuss something Network related for change today and I'm going to discuss this as sort of what I would consider a foundation for more in-depth networking discussions and I'm going to talk about Network layers and specifically I'm going to use the OSI Network layer model this is a deliberate Choice we'll get into that I say this is foundational it's not like you're going to use this daytoday at least I wouldn't expect that you'd use it dayto day this is more of an underpinning for what you encounter later on and I also do find it useful if I have a networking problem that I'm just not solving in the usual time we all have our tricks and you know first things we check oh something's not working oh well just go check this thing yeah I mean those kinds of fistic shortcuts that we use are completely valid but it helps also if you're facing a situation that doesn't meet those heris it doesn't meet those shortcuts it's useful to have the foundation to say okay if I step through this one layer at a time where is the problem and I can focus my effort on the the spot that's having the problem and not worry about the other stuff because either it's not relevant I haven't gotten there yet or it works and therefore I don't need to waste my time on it that would be great so you may have noticed the title of this video is something that looks completely odd because it doesn't say anything Tech related whatsoever well this is a pneumonic there are lots of pneumonics for the OSI Network layer model that we're going to walk through but the pneumonic that I have chosen to use in today's video is a penguin said that nobody drinks Pepsi what is this well this is the OSI Network layer stack from layer seven to layer 1 and I'm very deliberate in doing it this way because the higher stack levels are the ones that are closer to the user and then as you go down the stack you get closer and closer to the actual physical medium the layers here remembering that our pneumonic is a penguin said that nobody drinks Pepsi our layers are application at layer seven presentation layer six session layer five transport layer four Network layer three data link Layer Two and physical layer one okay that sounds cool all right fine before we get too much further into it and I'm going to discuss this in depth I would like to acknowledge that there are other network layer models out there for example the tcpip network layering model is similar and in some ways people might argue that it's more practical because it conforms more closely to how people experience and work with a network on a daily basis be that as it may I'm going to walk through the OSI layer model because it's a little bit more fine grained tcpip layer model only has four layers okay cool OSI has seven so it it takes for example tcpip the topmost layer is actually the top three of the OSI model so if if I break that down a little bit more I can be a little more fine grained in my troubleshooting that's just me and partly down to how I was taught if you're taught something different that's perfectly valid if you use something different in day-to-day networking that's also perfectly valid again this is just something that I normally use for troubleshooting and as a foundation to underpin my understanding of the rest of the network and how it functions if we go through these layers in order from 1 to 7 so we're going to reverse our Direction and start with Pepsi in this case physical what is the physical layer well the physical layer is broadly speaking just the physical layer it's the cables the actual wiring of the network or it could also be the radio waves that carry the network information between access point and client work workstation the physical layer covers a lot of very very heavy uh dense math and other information that quite honestly I do not consider myself an expert on and I honestly don't need to get into on a regular basis I do not need to get into what voltage is on the individual wires what is the bitwave signaling pattern in radio waves am I using orthogonal frequency Division multiplexing I probably am could I explain it to you no I could not there's a lot of the engineering on the physical layer which we can abstract completely as Network administrators in most cases and for the purposes of this discussion we're going to second layer the data link layer or according to our Nom pneumonic drinks data link is where we find things like mac addresses where we have ethernet frames as an Ethernet protocol um there are other layer 2 technologies that could be in use other than ethernet token ring is an example of that but most of the time what you'll be dealing dealing with is ethernet or ethernet based so for the purposes of this this discussion we can abstract that to ethernet ethernet is a I can never remember if it's CS CDMA or CD csma um but it is Carrier detect Collision sense multiple access I know these things but sometimes I have I have a little bit of trouble pulling them out of my head so carrier detect Collision sense multiple access cdcs Ma and what this means is that you've got a fundamentally shared medium and when one station broadcasts onto the network segment it also listens to to see if somebody else is talking at the same time and if it senses a collision then they both have to back off this is a very very very old understanding of how ethernet worked because ethernet used to have a bus architecture everybody was on the same segment these days we have switches instead of hubs switches essentially break this bus architecture up so that only one station is on each cable and it speeds things up dramatically so while I'm talking about ethernet in a more historical sense as a bus architecture keep in mind in most cases you're not going to encounter that anymore cuz we've moved past that we're so Advanced but Layer Two is where you have the actual data link the structure of ethernet itself you have address resolution protocol to determine Mac addresses you have uh CDP or Cisco Discovery protocol you have llddp or the generic link layer Discovery protocol these things all work on Layer Two so if they're not working you've got a layer two issue or a layer one issue layer three the network layer nobody the network layer is where we find Internet Protocol or IP we also find its companion the internet control messaging protocol I think is what that is icmp it's the protocol that gives us ping ping uses an icmp echo request message and then you get the icmp echo reply messages these work at layer three so this is where you get IP addresses or other network layer addresses if you're using the old novel ipx SPX protocol which is internetworking Pat excuse me inter networking packet exchange and I don't remember what SPX stands for you'll have to look that up ipx SPX used different style addresses but it ran at layer three of the OSI networking model you could use other networking layer protocols such as Apple talk those might have different addresses as well I don't know I'm not a Mac guy but for the most part IP has become the standard and so you'll see IP addresses all over the place and it's very standard to work with if you can ping an IP address then automatically that tells you Layer Three is working Layer Two is working as well because the way this works is you go from application all the way down to physical and then you transmit and then on the other side you go all the way from physical back up to application so if you can communicate on layer three that means that layer three and everything below it Layer Two and layer one is working cool if you can't pin on the other hand then there's no point in trying to troubleshoot something else like oh I wonder if it's DNS or I wonder if the web server is down if you can't ping then your problem is at layer three or lower and there's no point troubleshooting further up the stack so ping is a very normal I would say a very normal tool to be using to just verify do I have layer three connectivity yes no cool go from there layer four transport layer this is where we find TCP transmission control protocol or UDP the uh user datagram protocol again this is from memory so Wiki it if you want to be sure that I'm saying the right words um TCP UDP work on port numbers and where I said ethernet has frames and IP has packets TCP works on segments you'll you'll have uh a segment of of traffic that is then packaged by IP and into packets and then sent down to ethernet and packaged into frames and off it goes from there but TCP and UDP is where you have port numbers it's important to note that when you have an IP address with port number you're actually mixing layer three and layer 4 addressing information you've got a layer three address the IP and then a layer 4 address of the actual port number on that machine and there are six 6 5,5 and I want to say 36 ports everything from Port zero up to Port 65,535 if I'm remembering that last two digits correctly I know it's 65,500 something everything from zero to Port 1 2023 is reserved typically speaking you will not be able to connect to it um or set up something to serve that Port unless it is the correct program or unless you are root and have the privilege to use those ports the higher ports are called ephemeral ports they're the ports that a computer opens up to send just regular hey I want a web page traffic okay cool layer five the session layer said session is where you find the concept of sockets TCP and UDP will often open up a socket for applications to send traffic to this exists at layer five another protocol that exists natively at layer five is net bios net bios is not commonly used these days but it used to be a big thing in the windows world in the days of Windows XP and older and net bios also allowed you to do some file sharing standard file sharing today SMB has its own protocol and and everything else that's fine but if you were using file sharing overnet bios that was directly a session protocol session is also understood as the layer where it's just concerned about keeping the end points open and continuously exchanging traffic between two systems that's the session layer six presentation penguin um presentation has to do with the format of the data that's being exchanged in this case we could think of it as character and encoding there's a few different ways of encoding characters whether that's asy ebcd I um yes I know that was a lot of letters that I just read out don't worry about it uh the format for a JPEG file that exists at layer six the presentation layer the MPEG format for video also exists at layer six because it's all about the format of the information that's being exchanged then you have layer seven the application layer in the example that I'm going to use this would be something like your HTTP traffic where you're actually talking to a web server and asking it for information and it's sending it back okay what does this look like in in practice okay I connect to a web server and I'm going to look at the flow of the web server's respond specifically at layer S I am sending it text I am sending it a text request I would like to get forward slash the root of the website okay so it has that data it has to encode that into text because it's a text response or if it includes JPEG files or anything else like that it has to encode those into the relevant format for those files so that's going from the layer seven text request I want this and the server's response is 200 okay and here's some data okay 200 okay that is text when you go to application how do I encode this I'm going to put this into the the asy character set which is encoded like this into these values okay then I'm going to pass it off to my TCP socket which is at layer five the session layer then I'm going to put that over TCP Port 80 because the server is running on Port 80 and is responding from Port 80 and I'm going to send it to Port whatever the ephemeral Port is on the requesting side okay then it goes down to layer three the Network layer and it says okay this is headed for IP address 192.168.1.10 okay and it's coming from 1 192.168 80.5 I don't know I'm making this up then it goes down to the ethernet layer and it says okay well uh what's my default gateway because that's on a different subnet so I need the max MA address of the router I need to use ARP to get address resolution for the MAC address of the router okay now I can put that in the ethernet frame I pass it all the way down to the physical layer and the network card sends it out over the wire or over the radio if if we're using Wi-Fi there's a lot of stuff going on here absolutely if you can use ping to verify that your layer three connectivity is good between IP addresses then you can start looking at the higher levels you can say okay is my port open if the ports open and we've got traffic between the ports then I know that layer 4 is good you might skip all the way ahead to layer seven which is a valid consideration to make and just query the web server directly you can do this with tnet tnet as a protocol much maligned not very secure it's not secure at all absolutely but if you have a telnet client a lot of Internet protocols still fundamentally use text so as long as you don't have to go through an encryption layer like https which for most purposes you should be doing but for troubleshooting if you have regular HTTP you can use tnet to go tnet to this address on Port 80 you'll get a connection and if you type get forward slash you should see a text response come back from the server with a status code whether that's 200 okay followed by data followed by your HTTP page or whether it is um 404 not found or 401 on authorized or whatever it responds with you should see text come back the same is true incidentally of SMTP you can tell net to an address on Port 25 and you should get an smtb Banner you should be able to say hello and your host name and the server should you know say hello back and then you can type in quit and abort the connection if you can use telnet to get a connection to the application then you know that everything is working correctly from layer seven all the way down this doesn't help you if you've got a problem at a lower layer clearly but what are some things that might [Music] happen at a lower level that would block that okay then you start looking at is the portal open is if if I can ping but I can't get a tell Net Connection through well is the port open do I have the right address is the service located on a different server altoe what are some things that can happen to block the communication that would not show up even if you have a layer 7even full connection well what if it's a DNS issue if you're doing telnet to an IP address you're not doing address resolution which is done through DNS so you can confirm that you have a full layer 7 connection to the destination system but the problem is something else entirely so while this model is not the be all and end all it's just a foundation to help you with your troubleshooting cuz if you can say I've got a problem at a particular Network layer then you can troubleshoot that but the layer might need to be troubleshooted for various steps in the process not just connecting to a server at an IP address but also in DNS does my DNS request to the DNS server also go through this stack yes it does absolutely does it work maybe it does maybe it doesn't and then the the most important question do I get the right data back yes or no because you can have full connectivity working and still get garbage data if somebody's accidentally put something incorrect into the other side so there's a lot of things that you can troubleshoot but this hopefully gives you some more insight into the kinds of things that a network administrator keeps in mind while troubleshooting and some of the things that you can do to troubleshoot it as well I think that's more than enough for one sitting so I'm going to let you all go for now and uh absorb that think on it maybe do some more research yourself and I would highly encourage that but for now thank you very much for watching I am your next door nedman and we'll see you next time

Channel: NextDoorNetAdmin

Views: 36

Keywords: open system interconnection model, osi model, what is osi model, explain osi model, osi model lecture, define osi model, osi model in networking, osi reference model, osi 7 layers, 7 layers of osi model, presentation layer, session layer, transport layer, network layer, layers of osi model, osi, osi model explained, functions of osi layers, osi model layers, computer network layers, network layer protocols, osi layers in computer, techterms, data link layer, physical layer

Id: jRQyFZk-lbQ

Length: 26min 23sec (1583 seconds)

Published: Mon May 13 2024