Lecture - Network Layer

chapter 5 is all about the network layer and just to recap so we can put things back into perspective for the last couple of chapters chapter 3 in chapter 4 we've been talking about the OSI model and we've been looking at each of the particularly layer one so our layer seven was the application layer and that layers responsibility was to act as an interface between us and our end devices produces data data is then passed down we're going to skip over the presentation in the session we're going to go right to the transport layer which was the layer right before the network layer and the transport layer takes that data and it breaks it up what do we call it when we break up the data into pieces segments if we're using TCP what do we call it if we're using UDP Datagram is correct all right and regardless what it allows us to do is allows us to multiplex different conversations into one continuous stream so we're using our bandwidth more effectively this transport layer produces the segment which contains well if you're using TCP a whole bunch of fields and when do we use TCP I mean if you had to choose between TCP or UDP what would you pick and why would you make that decision and who makes that decision typically the programmer tends to make that decision so the programmer wrote this application and they know what kind of data they're dealing with and data can fall into two categories right it's either content sensitive or its time sensitive give me an example of time sensitive data videos voice why are those time-sensitive verse content sensitive because I know you might be telling me if you're watching a movie you want to be able to watch the entirety you can't just miss a part of the movie and expect you to understand the ending correct so you might want to say it's content sensitive and that could be true but what if it takes you a year to watch the movie would you want to watch it now and so we say it's time-sensitive more so than content sensitive because a movie's written up into what 30 frames per second 24 frames per second and so if you just multiply that by 60 that gives you how many frames per minute multiply that by 6 that gives you how many frames per hour multiply it by 2 it's typically how many frames per one movie correct do you think you'll notice if you miss maybe 10 frames or even 10% of the frames - the whole entire movie now I mean folks if you're getting 30 frames flashed in front of your eyes every second and you're missing three frames now you have a tolerance level anywhere between about 24 to 30 anything more than 30 we can't detect it anything less than 24 you can detect okay so we build their movies from 24 to 30 frames now I'm not counting video games artificial stuff it takes double so if you're playing a video game the frame rate should be 60 frames per second but for natural images true color images we're saying about 30 frames per second so we use UDP in this case because we say what really matters is that they're there in a timely fashion so I'm not buffering all the time so I watched two seconds of a film wait two minutes to watch the next two seconds that really takes the enjoyment out of it could you imagine telling a joke or watching a funny movie and then you miss the punchline it took two minutes later to get it so UDP is about getting it there but UDP can't give you reliability so what happens when the movie starts getting choppy er start dropping frames what's that you the user are going to have to hit refresh or pause the YouTube video and drag so I dragged back your slider the timeline but you're managing that so UDP only gives us four fields that's the source port the destination port the length and the checksum the only two fields I really care about when it comes to UDP are also the same fields that are in TCP the source to the destination port addresses when do we use the source address and how do we assign that when a client is initiating a conversation when they serve our another client this client will automatically assign dynamically a source port address to the segment that it's about to ship out and that could be anywhere between forty nine thousand one hundred and fifty two all the way up to 65535 where'd I get those numbers a port address is 16 bits to raise to 16 is 16 65536 but we go from 0 to 65,535 an organization I'll be asking this in your review I'll be asking it on on this Wednesday's exam known as IA na basically manages will organizes port addresses and they have broke that range of port addresses into 3 parts well-known which go from 0 1023 right registers which go from 1024 up to 49 thousand one hundred fifty one and then dynamic all right well nodes are typically used for like open soft sorry services like HTTP FTP pop SMTP DNS DHCP the reason why we call them well-known is by the end of the semester you guys better know them right in fact a couple exam questions I asked for Wednesday is and you'll see in this review like what port address does DNS use what's that odd DNS not HTTP 53 right what about DHCP 67-68 yeah uses two of them 67 and 68 right you might want to get to know some of those okay folks especially before this exam I do ask them but regardless the client assigns the application that's making the request a dynamic address so that when the data comes back the operating system knows what application is requesting this data so you can think of it as software identification in fact the upper layers have no clue what the transport layer does and the lower layers have no clue how many applications are making the request all they're seeing is a continuous stream of data coming from the transport layer so what's the destination port address used for if the source ports used to identify the application that the clients using to make a request what's the destination port used for yeah we don't call it an application so you're right that it's to identify what quote-unquote application that the other end device is using instead of calling an application what do we call it protocols or rules to govern it it runs in the background all the time usually runs on a server daemon or a service or a process right in fact that's another question I put in the review that might be seen on this Wednesday's exam what is the difference between services and applications you use an application the application uses a service that's typically ran on the server okay now I say typically but most modern operating systems are changing that you guys have a whole bunch of services that are running on the background of these computers right here and they're not considered servers but what exactly is a server just a piece of equipment dedicated to be running all the time to respond to requests correct can you guys give me a couple of servers that we've set up in this classroom using packet tracer with that DHCP server correct and what did that service allow us to do for our network yeah basically assigned IP addresses in fact and I did this when I was creating this file last night I was really hoping that I had a DHCP service but I didn't I had to go through all 20 of these or 24 of these devices and configure them so they had an IP address it wasn't fun was very boring and I kept it tradition I went from like PC one I called this 192.168.1.1 then I went to two and called that dot two and then this dot three and so on right in Chapter five what we're going to learn about is how to divide these lands so they're broken up into smaller more manageable pieces to give us better performance in fact the whole role of chapter 5 is focusing around the network layer part of chapter 5 depends on your understanding of chapter 6 as well which I'm a little disappointed because you really can't get the chapter 6 without going through chapter 5 so I'll be introducing some chapter 6 theory today and probably tomorrow in class but the idea is we're focusing on the network layer the network layer produces a PD you called a even though chapter 5 stuff is not going to be on this week's exam you guys know the answer this question what is the PD you called for a network layer packet why do you know this question because in Chapter 2 the only thing we learned about was the OSI model and the TCP model in fact it might be a good idea to know the difference between the TCP / IP model and the OSI model remember they both accomplish the same task just how they divide the work up it's where they differ so what does a pocket produce well it seems like from here on out we're going to be talking about addressing when we got to the transport layer the big addressing that we're talking about with source and destination port addresses we get to the network layer the addresses that we're going to be talking about going to be called logical addresses logical is something rather different if you will example of a logical IP as our example the logical address would be an IP address it's actually one of the most popular ones but it's not the only form of logical addressing it will be the only one that we will discover in this course but appletalk is another example of a network layer protocol Novell IPX is another one but this one's the most popular one because it's an open non proprietary protocol because it's open it's been accepted by many many different corporations and hence we've been putting it in everything including our Xbox and yes your refrigerator will have a logical address and most likely to be able to understand the IP address Samsung is releasing one the end of this year 2012 you guys seen it touch screen yeah refridge that has an IP address has a touch screen on it in fact you can get the waggons app installed on this refrigerator hey that's all what it's about right technology becoming cheaper and cheaper why not justify paying five thousand dollars for refrigerator because it has a tablet on there correct and if you're any of you're thinking about it yeah exactly and if you're thinking about it in your Samsung what does samsung also make phones computers phones tablets TVs correct so what does Apple not make refrigerators washing machines dryers so they're looking at that customer it's a little obsessive and saying look I got it everything Samsung in my house so not bad marketing but regardless absolutely our refrigerators our appliances will have IP addresses maybe for managing sake maybe for convenience sake but yeah bang up my washer my got to reboot my refrigerator yeah that might happen so we have to ask yourself well as long as Microsoft isn't in handling it will be good as long as we ask ourselves why are we giving out these IP address what is the role this layer well it all stems down to this is not a good thing the fact I have a lot of devices swarming into the switch and they're trying to communicate is going to degrade my network performance and hence the name for the network layer we got to talk about what exactly makes up a network and how do we break our networks up and keep them still able to communicate with each other but make them a little bit more user friendly a little bit more better to manage and so the network layer uses logical addressing to create this hierarchical approach to allow us to divide our networks up into smaller subnets to make them easier to match and then to be able to do what we call end-to-end delivery who initiates the conversation and network the client write an end device you use software the software uses a hardware to actually ship out the request so you're initiating this what does that request go it is planning to go through a series of intermediary devices what eventually reaches another end device correct so this addressing scheme logical addresses whether it's IP address or whatever is designed for end-to-end delivery looking at this diagram that's going to be sort of rather foolish I mean it's not that I have to go through any other network because they're all in the same network how do I know that these end devices are all in the same network look at the intermediary device that I'm using to connect them all together this is a switch another review question a switch is a device just like a hub that's used to connect local devices together correct how many devices can I plug into a local area network typically depends on how many switches I have and how many ports are on the switch correct could I edit another switch to this local area network and then branched off another 23 or 24 devices off of that absolutely when do I stop yeah how many devices could I fit onto this network if I keep on adding switches and switches and switches when I grow it by the way it's not a good idea to be doing this but when do I stop when I run out of IP addresses it's absolutely right because folks we use this address to deliver the message from end to end devices if an end device doesn't have an IP address it can't communicate on our network correct by the way we're just jumping this down there are other delivery methods out there that don't that doesn't use IP addresses but will still allow you to deliver messages and for em like point-to-point protocol killin how many main streets exist in this country main streets exist in this country bones so what makes our Main Street unique then another main street let's look at these addresses in fact we usually say one Main Street and this is an example what we call a hierarchical address I don't know if corny has a Main Street but let's just say they do and let's say Corning's the address that we're trying to ship to a packet - is going to be one Main Street corn in common New York one four eight three zero zip code has five digits is that right folks yeah these are protocols you got to follow this so we start looking at this Main Street can be very common how many Main streets are actually in Corning out there should only be one right there should only be one right because if there was two main streets in Corning look at the confusion this would cause are you on this Main Street or you're on that Main Street well I'm on that Main Street whatever that Main Street is there should only be one Main Street in Corning how many Corning's exist in this country there could be a bunch of them right what makes this Corning unique then another Corning in another state the fact that I'm in New York what it makes sense to give to States sorry to give to cities the same name in two states in fact what are the rules we've been following no two devices on the same network can have the same ip address correct or the same name and so a post-office stuff is very hierarchical to the fact that we start off with technically country but we assume that if you're sending something locally you don't have to add the country in there but if you're sending something abroad you must add the country code or the country initials then it goes to what steak and then in each of those states there's going to be cities and in each of those cities there's going to be what streets now everybody's asking where does the zip code come in what do you and I care about what makes data easier for us to represent using numbers or letters I mean your parents gave you guys a name and not a number correct they don't say hey child number one come here it's easier just to say Bob come here or Nick come here than it is child number one child number two it's easier name child 1 child 2 that way but you know likewise here we've automated the system right when we're passing messages through all through that our scanning system is actually looking for zip codes more than they actually look for city names the other thing is cities can be much much larger in fact where I'm used to come from they used to be like 20 zip codes that make up our city just like there was like 10 area codes that would make up our city and so when used to want to send a letter down the road it might be like this 1 4 8 3 0 - some other number and we call those like boroughs all right or districts but nevertheless us just using Corning Main Street one works just fine for for what we do but then we have to add other things like zip codes for automating the process in fact what service have we learned about that actually does this for us when we're trying to act as a web page that takes a name it converts it into a number this autumn ization DNS so we look at logical addresses we can see that we have this hierarchically this segment going on where we break our network up and to pieces how do I do that well the three rules that come to breaking a network up well I shouldn't say three rules let's say three techniques it's going to be off of geography I kept on hearing that delete Tom you were saying that another one's going to be by purpose and the last one is going to be by ownership or by security it depends on how you wanted to dictate that and I don't want you guys to think that you got to follow one of those three techniques and they are just simply techniques in fact you can probably take two oh sorry geography plus purpose and add security in there to make your final decision let me just give you an example of how we can use geographical location to represent our networks I can call this Corning and then I can call this one pine City and call this one down here Mansfield and I can call this one over here bath a lot of distances between those networks correct and what defines a local area network geographical size the fact that it's managed by a particular or a single organization or a particular individual what else by the size of the number of users if I was doing this I wouldn't have the luxury and being able to connect them all to one switch that is if I'm following the ethernet standard the maximum distance I can have between an end device and an intermediary device is 100 meters it's about 3 328 feet give or take I think the distance between baths and Corning is more than 328 feet so what would I need to do to be able to get these segments or broken up into tinier pieces which we call subnetting subnet it to be able to handle this geographical range well we've been talking about lands local area networks and now we're going to do some nother type of network called a wide area network and a wide area network is when we take two or more networks and connect them together using a particular device and that device is known as a router it is an intermediary device that acts as a gateway or a way out of a network onto another network now typically when I'm dividing my networks up I'm not really focusing on geographical locations that's because the networks I you manage are the ones in my home so another way of taking my networks and dividing them up is by purpose how might I take the computers in my house and divide them up and let's just still use these four sections now this is a whole network all right so we have children adults by just doing that this could also introduce some security some parental controls correct by separating these into their own little networks I can implement a whole new policy with these computers then those computers over there I would forbid my adults to go on Nickelodeon but I'm like you guys are thinking something else right yeah yeah yeah Monday I'll tell you a lot but I might permit that for my children to do that but you know what what about these two what are they what would they possibly represent I'd said it earlier let's see appliances apply us and I don't know how you guys spell that appliances something like that help me out there is it kind of yeah we'll see what else might I have one another what other area well automation that might fall under appliances what about fixed devices like my server printers what else my router I know that sounds funny in fact I might have a series of routers on my home and in other classes you guys will learn that you probably want to create VLANs if you're doing within a smaller geographical locations but for now let's just say I have some permanent devices on my network I have a media server I have a security server I have a backup server I might put them in their own group I also have printers routers scanners Network DVD players and so on and I might want to put them over here why am I doing this why am i taking this network and cause myself more trouble when it's just as simple and cheaper for me to buy one switch and throw them all on there and say it's fair game well one's inert like I said here I might not allow my dholtze to have access to Nickelodeon where I might for my kids this Institute's security right what else well let me give you this demonstration for devices to communicate with each other using IP addresses they need to be able to map these addresses to physical addresses in fact in a couple of weeks we're going to be getting into this next layer called the data link layer and this layers all about the physical stuff in fact they assign physical addresses to every end device on a network every interface card has we call a MAC address a media access control address in this particular scenario everything is local I really don't need a gateway to be able to communicate with each other two things happen for them to be able to communicate with each other one I need to make sure that the packet that I'm sending to the end device that is exists on the same physical network as it does in the same logical network translation they both have the same network address so in tomorrow's class we're going to be exploring the structure of an IP address and house made up of two parts the second thing is I must know what the physical address is of that device if it's a local device the way we find that out through an ARP request an address resolution protocol folks we talked about a dns request now we said that was a resolution protocol what do I mean by a resolution protocol when I basically look up something right when I'm translating from one address to another the address resolution protocol that we've explored was dns where we resolved a domain name to an IP address our we'll take an IP address and resolve it into a physical address so let me do this using a simulation I'm going to go over here at a PC one I'm going to go to the desktop and I'm going to click on the command prompt then we'll type in ARP - a so let me write this command up so you guys know it so there's a space between the P and the dash and when I type that in there you're going to see I have an empty table and what this table is going to explore is my IP address so in this case it's 192.168.1 and the physical address that represents that now I know who I am and I know who might what my physical address is what I don't know is the person I want to talk to so if I want to talk to let me ping 192.168.1.1 T I'm going to stop this process I'm going to send out an ARP request you can see on my PC I have a green envelope representing that ARP request now depending on where this packets destined to I know since they both are the same Network addresses destined to stay in this local area network I'm going to send this up request to my switch and the switch is going to broadcast to everybody why is the switch broadcasting to everybody because we talked about the difference between a switch in a hub and we said the only time a switch has to broadcast everybody is when it's doing what when is building its MAC table right when it knows what ports are out here but in this particular case the reason why the switch is going to broadcast to everybody it's not because it has to build this MAC table as much as the ARP isn't destined to any particular device it's saying hey if you have this IP address I need you to send me back your physical address data is delivered from device to device using physical addresses logical addresses allows us to go from network to network okay at this particular point I need to talk to somebody here my switch is going to manage that and mice which handles layer 2 addressing MAC addresses so if I want to talk to this device I have to supply the switch with a MAC address why does a switch need the MAC address so they know what port to send it out on right because a switch likes to establish private conversations between end device and end device we good about that hubs don't in fact I probably don't even need to send an ARP request if I'm using a hub even though my computer would do it technically I wouldn't need to why not because anything that comes in to a hub gets copied and sent out all other ports correct the only way I can have better control over that is if I add another layer of control another type of addressing in this case a physical address so my computer when it builds its frame to be able to ship it to the switc it's going to need a physical address so let me hit forward are you gonna get skinnier on me no I guess have to zoom out a little bit sorry guys resolution homes a little bit different than this one so here's that ARP request going now remember I said I'm going to ping computer 20 so I typed in 192.168.1.2 NT we good about that before I can actually pin as you can see I'm just dealing with an ARP it's going to send out this message if you will to the switch the switch is going to send out all other ports except the one that received it on me good about that what are all these other computers going to do except for computer 20 going to ignore it it's going to drop it why are all these other computers with little red axis and y is 20 just good with it because they said look if you have an IP address of 192.168.1.2 NT you need to tell me what your MAC address is with your physical address is correct no two computers on the same network can have the same IP address hence only one other computer on my network can have that address and should be able to respond back to this our request we're good about that what happens if all these other computers are in the middle of communicating with their friends they have to stop they have to listen to this ARP request they are being bothered by something that doesn't really pertain to them correct why because if we're dealing with electricity folks and this is receiving data from somebody else and this switch gets this ARP request after it's done setting the last fret a solid frame that's which is going to send it out stopping everybody else from communicating because what does the communication process entail sending data and also what receiving it and you can't continue this is like being on the phone with your friend and call waiting clicks through you got to stop your conversation to answer call waiting just to resume it what happens is more and more people are sending these are pre quests in fact let's not make it so specific and let's just say what happens if more and more devices are broadcasting across your network what happens to the performance degrades regardless whether you're using a switch or a hub it will degrade and that is the chief reason why we need to break these networks up sorry this network up in the smaller pieces so that the broadcast is only within the particular subset in fact we call these broadcast domains for that particular reason so let me hit forward and as you can see only this computer is responding back to the switch is this going to be copied and sent out all the others how do we handle local delivery using physical addresses physical addresses for local delivery right this witch knows about PC ones physical address because PC one initiate the conversation it came in to the switch the switch said oh yeah I know you your port one we good about that now it sent out that off request everybody else then we're at PC twenty PC twenty is actually responding to the ARP request now the switch knows about PC twenty being plugged into port twenty if that's why I plugged it into would it be okay for PC twenty to address only that particular device sort of makes sense it should have the IP address and that's what it does why should I bother everybody else now that I know PC ones IP address and now you're saying well how does PC - it's our PC twenty know about PC ones physical address because PC one had to stamp it here in its frame it's one of those things about this chapter you got to explore other chapters to get this we'll explore that technique in another that's our chapter seven if I remember correctly chapter 7 or chapter 8 but until we get there I want you guys to feel pretty comfortable that the switch tries to manage individual conversations by using physical addresses before I can actually do that however I need to make sure that my ARP table on my computer is being built so I'm going to finish this simulation by heading forward it should say done just going to view previous results and now I have my replies the important thing is if I come here and I type in art - eh I see let me move that up for you that the physical address for 192.168.1.1 T is this particular one zero zero d0 it uses a hexadecimal a physical address and Ethernet is 48 bits okay typically I've seen it where it's two digits followed by a colon then another two digits followed by a colon Cisco uses this little decimal dot notation so they do it in two groups of four 4.4.4 now nevertheless it still adds up to 48 bits like I said you'll explore that if I will be exploring that in another chapter if I go or PC 20 and go to the desktop and click on command and type in ARP should there be an entry in this table and whose entries should it be the one who are received it folks it's very full duplex if I'm sending something I got a stamp my name to the package correct and then underneath my name what am I going to write if I'm writing you a letter my street city state and zip code correct if this is the first time you receive something from my new home what are you going to do next you're going to write in your address book why are you going to write in your address book so it's there for you to quickly look up without bothering me or anybody else to get it correct so every computer will have an ARP table just like they will have their own routing table just like they'll have their own one when it comes to resolving domain names to IP addresses they're DNS entries correct the call that the DNS cache so let's get into breaking these computers up in order for me to break these computers up the first device I'm going to have to do is delete the switch so I click once close out a dialog box hit the Delete key it's going to say are you sure you want to do that now they're all disconnected correct the next thing I'm going to do is just take these devices and move them away from each other so I can organize them in a more usual friendly format I'm going to grab these over here whoops move them in a circle so you guys can see that this is its own private little in-game gathering and what am I going to put in the center switch because I want to create a local area network correct correct in fact I told you a wide area network as a bunch of local area networks connected together all right in the interest of saving time it's going to come down here to lightning bolt hold the ctrl key and do the auto connect correct and I'll do six to the switch then seven then oh nine ten eight and eleven at the escape key and hit the fast-forward time so they all lit up I'm going to go do the same thing to the other Network remember this is the children Network and I'm going to the same thing mom and dad's Network and add a switch between those I'm going to fast forward that you know what I don't want to buy a separate internet connection for my children Network and for my adult network granted sometimes I feel like we need that especially when they're getting into YouTube they're tying up all the bandwidth but what have we learned in the other chapters what can I do about controlling their bandwidth what's that service starts with a cue QoS quality of service allows me to create policies of traffic that's leaving my network well here's the catch by using a router setting up gateways outside of these lands I can set policies for each network and I can say anything that's destined to this network here I want you to only give it a couple of kilobits per second anything that's destined to this network over here I want you to give more in fact I can even filter things out by IP addresses if somebody comes into my network and they don't have the following IP address deny them access not only a router helps to implement security but I can also use something else known as a firewall to block certain applications for each of these networks if there are certain websites that I don't want these children to access I can set it up in a Content filter in fact one of the things I told you guys about and I said they are not going out of style is maybe we can set up a hub and off of that hub I'm going to put in a server more or less a monitoring station why do I choose to use a hub in this case because what I gear to see in a second may I add a router here and a router here and then those two routers going to connect to this hub in fact let me do that so you guys see that so here's one router here's another and then here's the last one I'm going to add to it I'm going to connect that router to this network I'm going to connect this router to that network sorry that switch to this router then we connect these two routers to this hub and then this hub to the bottom router why would I do something like that and where would this router be connected to my internet connection right why would I set up a hub in this particular scenario first to switch or why would I even just have one router this router connect to that Network and also this network as well as the internet which I could do this one's very costly to implement I would get better performance out of this and I would also get more control but the question comes back is why would I put a hub right here between these three routers and hook a server off of that remember I told you I'd call that more of the monitoring station than I would a server so now I get to see what my kids are getting into and when my kids know that no do I have to go to any one of their computers to install some kind of parent software my hub will do that because anything that's going out has to go to this server gets record it and then I get a nice little op progress report from my children if you will without them knowing it do you think that happens in corporate America absolutely yeah DC by breaking my network up into smaller pieces I have more control over it I can assign better policies so I can blank it one group one purpose so this could be like my HR people this could be my faculty this could be students this could be administrators and I can set different layers so are different levels of security you know the other thing that allows me to do is it allows me to keep data within this and if it's closer to this network it should do what should perform a lot better correct so if my kids always want to watch movies and I don't have to change DVDs maybe what I can do is put a media server onto their network and it's going to contain that traffic that bandwidth here locally so the video should load faster they're not going to argue oh well so-and-so has got the TV if they all have their own pot s are their own iPad by storing our movies into one central location by taking our DVDs and ripping them and putting them on our server each kid can watch the same movie at different times at different parts without bothering our network this is just an example of how you can take a network and divide it up by purpose implement security and get better performance the key thing here is security and performance I'll see you guys tomorrow we'll get more into this will talk about the IP structure and how it's actually implemented

Channel: Nicholas Andre

Views: 27,848

Keywords: Lecture, Network, Layer

Id: NbV6Zj87JwM

Length: 46min 55sec (2815 seconds)

Published: Mon Sep 24 2012