Network Layer Characteristics (Module 8) - PDF

In this lecture, we will study the network layer. This is module eight of the Cisco introduction to networks lecture series. If you\'d like to learn about other modules, I will leave a link in the description for the lecture series playlist, and you can go ahead and check it out in my YouTube chann...

In this lecture, we will study the network layer. This is module eight of the Cisco introduction to networks lecture series. If you\'d like to learn about other modules, I will leave a link in the description for the lecture series playlist, and you can go ahead and check it out in my YouTube channel. We will cover the network layer characteristics, the IPv four packet, the IPv six packet, how a horse routes and the router, routing tables, net. Network Layer characteristics. So remember on the OSI module model, the network layer is the third layer from the bottom, so we have physical data, Link, trial, network, transport, session, presentation and application. So when they are communicating between host. Now we are looking at the layer called network layer, which is on top of the data link layer and just below the transport layer. Network layer, protocols forward encapsulated transport layer, PD, use between the host. So that is a very important concept. So just remember that term. So the the this concept, so the network layer protocols forward encapsulated transport layer PD use between hosts. So it takes the network layer is responsible for that transport of the PD use between the host. So eight. Network layer provides services to allow N devices to exchange data. IP v4 and IPv six are the principal network layer communication protocols. In our previous modules, we briefly look at how IPv four different from IPv six and the network layer use those two protocols for communication. The network layer performs four basic operations, addressing and devices, encapsulation, routing and de encapsulation, IP, encapsulation, IP encapsulates the transport layer segment. IP can use either IPv four or IPv six packet and not impact the layer four segment IP packet will be examined by all layer three devices as it travels the network. IP addressing does not change from source to destination. So remember when you are communicating within a LAN and when it is going across multiple switches or routers within the LAN network itself, the source and destination IP addresses does not change and until it actually goes through some kind of a NAT. So that\'s what it says on the bottom. Nat will change addressing, but will it will be discussed in a later module. But for now, what you need to remember is, when you are communicating between two end devices within a LAN network, the IP address the source and destination address does not change. And NAT is basically network address translation that is the function of your, for example, your home router that allow you to connect to the internet. And again, we will discuss this in a later module. What are the characteristics of IP. IP is meant to have low overhead and may be described as connection list best effort and media independent. I will go through each one of them in depth in the next few slides, but for now, just remember those are the three important things about IPs. So the first one, he says, IP is connectionless. IP does not establish a connection with the destination before sending the packet. There is no control information needed, such as synchronizations, acknowledgements, etc, the destination will receive the packet when it arrives. But no pre notifications are sent by IP. So basically, the sender doesn\'t need to let the receiver know that they there is a packet coming towards them. There is no pre notification needed. If there is a need for connection oriented traffic, then another protocol will handle this, such as TCP, which is at the transport layer. And we will also talk about TCP and UDP in a different module. But for IP protocol, it is connectionless. It doesn\'t need. To let the receiver knows that there is a packet with particular IPS arriving at their destination. Best effort IP is best effort. IP will not guarantee delivery of the packet. IP has reduced overhead since there are no mechanism to resend data that is not received. IP does not expect acknowledgement. So IP packets doesn\'t expect the receiver to acknowledge that the packet has been received. IP does not know if the other device is operational or if it is received the packet. In other words, just like mentioned before, it doesn\'t matter for the sender whether the packet has been received by the receiver. It doesn\'t receive any confirmation back from the receiver at all, and the IP is media independent. IP is unreliable. It cannot manage or fix undelivered or corrupt packets, as I mentioned before. It cannot retransmit after an error. IP cannot realign out of sequence packets, and IP must rely on other protocols for these functions, such as TCP, for example, IP is media independent. IP does not concern itself with the type of frame required at the data link layer or the media type at physical layer. IP can be sent over any media type, such as fiber copper or wireless. So the IP packet can travel through a copper wire, wireless, fiber optics, any media, because it\'s just IP is able to operate on any of the media types. The network layer will establish the maximum transmission unit, or MTU. Network Layer receive this information, control information, sorry, network layer receives this from the control information sent by the data link layer. The network then establish the MTU size. Fragmentation is when layer three splits the IPv four packet into smaller units. Fragmenting causes latency and IPv six does not fragment packets. For example, router goes from Ethernet to a slower Wang with a smaller MTU that will result in fragmentation. So if you have a router that is connected to a fiber optic High Speed Line, but your internal networks are copper that may cause fragmentation in IP transmission, that\'s all you need to remember for your exams and quizzes for this module when it comes to my fragmentation, because we are not going to go into depth of how fragmentation works in this particular module, but we will in the future, the IP v for packet the IP v4 packet header have couple of things that you should be aware of. IP v4 is the primary communication protocol for the most networks layers in modern day. The network header has many purposes. One of three of those would be it ensures the packet is sent in the correct direction from sender to the destination. It contains information for network layer processing in various fields. The information in the header is used by layer three devices that handle the packet. So those are couple of things, three things that the IPv four packet header does, and we will look into little bit in depth on all of them in next few slides. The IPv for packet header has the following characteristics. It is binary. It contains several fields of information, and typically it is read like when you look at a when you try to represent that on a piece of paper like this, it is read from left to right, and four bytes per line, the most common and the most not the most common. The most important fields are the source and destination address. Remember, every packet must contain the source and destination, and those are very important for operation of packet switching. So that is the most important part of the IP v for packet headers. Yes, protocols may have one or more functions when you know, when used with other protocols. And again, I will go into depth in a different module when I talk about that. But for now, or if you just look at your right hand side, you have a diagram of IP v4 packet. And you can understand, by looking at it, we have a destination address and the source IP address. Those are the most important things. And then we have the time to little protocol check, some identification, the flags, and you know, everything else. And we will go into depth of a IPv forehead soon after, but for now, just remember, those are the items that you will see on IPv four header. So what you need to remember for this course and this particular module is the significant fields in the IPv four header. Those are version differentiator, services, header, checksum, time to live, or TTL, the protocol, the source IPv four address and destination IPv four address. So those are the important things that you should get out of it. I will show you another diagram comparing IPv four and IPv six headers, and you should also familiar with the differences between the two headers. So for IPv four packet headers, what you need to remember is there\'s a version. This will be IPv four, as opposed to IP v6 with a four bit field. And there\'s a differentiator services, such as used by QoS diff, serve field, etc, etc, tos, also and header checksum, which detects a corruption in the IPv four header. Remember, it\'s like a fingerprint. Time to leave. It\'s a layer three hop count when it becomes zero the counter. Sorry, the router will discard the packet so the you know, you don\'t get congestion with having a lot of packets that are never used in the network. So that\'s being controlled by the time to leave or TTL, the protocol is the IDS next level protocol such as ICMP, TCP, UDP, etc. So it will like, given what data contained within that protocol header, the packet will know that you know what type of protocol it is going to be used in by the next level. For example, ICMP is one, TCP six, UDP is 17. You should actually know these numbers for your exams and quizzes. And you should know each one of them. You know what they do, like each one of these sections, and the source IP address, which is a 32 bit source address, and the destination IPv for address, which is also a 32 bit address. So this is going to be the source and destination addresses. Those are the very important ones, because if they don\'t have one of either one of them, the source or destination, the packet is not valid, right? So that\'s very important for delivery of the packet. So let\'s compare the IPv four and IPv six headers briefly, even though we don\'t go into depth of each one of them. So the IPv four header on your left hand side, you can see that and the IPv six header on your right hand side, you can see on the right hand side diagram on the IPv four header, we have the source and destination address, just like IPv six header, also have the source and destination IPv six address, so it has IPv four source and destination and this one has IPv six source and destination address. Notice, both of them do have the source and destination IP addresses. However, the big counts, like how big the use addresses are different, because IPv four is 32 bit and IPv six is 101 28 bits, and there are some fields in IPv four that is not found in IPv six, such as the header checksum, the options and padding information, the identification, the IHL, etc, etc. But there are items that you always find other items, such as, for example, version so see, there\'s a version header up here and version head up here. And also, there are some headers in IPv six and IPv four, both common to each other, but the position of the header is different, such as, for example, the if you look at, for example, in here we have the total length. And total length here we call it like, you know, payload length, instead of saying total length is kind of like a payload length, so a TTL. Time To Live is in IPv four, but in IPv six, we call it hop limit. So kind of TTL and hop limit doing the similar functions, the position of which is on the header is different, and also naming convention is different. So do you need to know the differences between IPv four and IPv six headers for this particular class? Yes, I would say at least you should have a very good idea about how IPv four and IPv six headers are different in this class. Otherwise you might not understand all the concepts that we will be covering in our future lectures. So this slide is a very important slide you should buy deposit and come back here and check it out, because that will give you a better idea about the differences between IPv four and IPv six headers. There\'s a video on your Cisco NetAcad that look into the IPv four headers in Wireshark. Wireshark will allow you to examine those packets in depth. However, if you do not have access to the Cisco NetAcad, I have posted a copy of that video on my YouTube channel. I will leave it in our description of this video, and you can go ahead and check it out. But if you do have access to Cisco NetAcad, just go ahead and you can check the video called Sample IPv four headers in Wireshark, or go to my YouTube channel and search this, or check the link in my description, IPv Six packets. Limitations of IPv four that we have a global depletion of IPv four addresses, so we basically ran out of IPv for addresses because everybody have a cell phone, everybody have connected device. And most devices in the world now are connected to a network. And there are more and more people around the world, in developing countries are now being connected to internet and networks. So we are literally actually running out of IPv four addresses. The other one is the lack of end to end connectivity. So to make IPv four survive this long, to 2022, Private Addressing and network created, this ended direct communications with public addressing. So what that basically means is, when you have a router at your home provided by, let\'s say your service provider, the your internal IP addresses are different from your external IPs. So when you communicate to the internet, let\'s say you sitting on in front of a computer, and you access the Google, for example, google.com or sanuja.com when you access sanoji.com What happened is your local computer, which has a local IP address, such as like 190 2.1 68.5 dot 10, for example, go to the router, and then router will use the network address translation or call NAT to communicate to the internet using its external IP address, saying, Hey, this guy needs sanoji.com website delivered to its computer. And then what\'s going to happen is that the external site doesn\'t see your internal IP address. It is being translated through network address translation called Nat, through your router. So we will go into depth of this later in a later lecture. But for now, what you need to understand is Nat actually separates the internal and external networks in at the IP level, especially, and as a result, it increased the network complexity. So Nat was meant as a temporary solution and creates issues on the network as a side effect of manipulating the network header addressing as a result. So the NAT is causing more network complexity that we really don\'t need, and that also causes latency and some troubleshooting issues. Let\'s look at an overview of IPv six. IPv six was developed by the Internet Engineering Task Force, or E, sorry, i, e, t, f, i, p, v6. Overcomes the limitations of IPv four. It improves the addressing space, and it improves the packet handling, and it eliminates the need for the NAT so how it goes about increasing the addressing space is that we are switching from having 32 bits in IPv four 228 bits addresses in IPv six, which is significantly increasing the number of IP addresses that can be assigned. Like, for example, IPv four will be around that, and IPv six is around that. So IP v6 can provide 340 under silly number of IP. Addresses, as opposed to IPv for just 4 billion, it improves packet handling because it simplifies the header with fewer fields, and we don\'t even need network address translation, since there is a huge amount of addressing, and there is no need to use Private Addressing internally, because we now we have way more than what we needed. IPv four packet header. Fields in the IPv six packet header, the IP v6 header is simplified, but not smaller. The header is fixed at 40 bytes or octet long. However, some IBV four fields were removed to improve performance, such as flag, fragment, fragment offset and header checksum. So on the your right hand side, you have a diagram of packet header. And again, we\'ll go into the depth of this in next few slides, a little bit significant fields in the IPv four header, so we went over this before I\'m going to quickly go this again. So we have the version, traffic, class, flow, label, play, payload, length, next, header, hop limit, source, IPv four, address and destination, IPv for address. I went over the descriptions before and previous slides, so I\'m just going to skip through this. But just remember, these are the significant fields and IPv four header, the IPv six packet may also contain extension headers or eh. Eh headers have the characteristics of providing optional network layer information, and they are optional and are placed between IPv six header and the payload, and may be used for fragmentation, security, mobility, support, etc. Unlike IPv four, the routers do not fragment IPv six packets. That\'s a very key concept that you should remember. Unlike IPv four, the routers do not fragment the IPv six packets. Again, there is a video in your Cisco Net Academy, if you have registered with the academic institution.\ \ Know you have access to Cisco NetAcad, the video called Sample IPv six headers in Wireshark. But if you do not have access to Cisco NetAcad, I will leave a link below in the description, and I have posted to my YouTube channel the same video so that you can go ahead and watch it and learn it. If you are currently going through this lecture, I would recommend posting this video and check that video first and then come back to the complete module. How are host routes, host forwarding decision. Packets are always created at the source. Each host device creates their own routing table. A host can send packets to the following, so the host can send it to itself. We call that a loop back. So IPv four, loop back going to be 170, 2.0, dot 0.1, and IPv six going to be these two dots and one, and that will be IPv six. So ping, like if you ping 121, 127, dot 0.01, that is a testing the ITCP IP stack on the device that is working correctly. So we just checking the device itself to see if the TCPIP stack is working on the device itself. We can ping 172, 001, in IPv four, for example, local host destination is on the same LAN will have that those local hosts and the remote host, which are devices that are not on the same LAN. So like, for example, in this diagram, a local host going to be like in the same land. So you\'re going to have 192 168 10, dot 15 here, and 192 168 10, dot 10 here. So these are local host right here, because it\'s behind the, you know, one side of the router which will have a port associated with 192 168 10.1 for example, a remote host going to be something that is after that net translation, or after that router on, this case, on the right hand side, and that would have a different IP address and different subnet. Just in case you guys are wondering, what are subnets? We will talk about that in depth in a different video and a different lecture. Just remember, like same subnet basically mean this the address with the first 123, the third 123, all these three octets are the same. So 192 168 10 is dot 10, and 191 6810, dot 59 the same subnet on the same network. And that would make it actually one of the reasons why it is a local hosts, as opposed to a remote host. So this one could have like 192 172 5.1, for example. So that we\'re going to be a complete different subnet and it is outside that network. And again, we will go into depth of those subnets and how, how you can create variable subnets in a different video for now, just remember local host versus remote host, that that\'s how you distinct them. This distinguish between them. The source device determines whether the destination is local or remote. Method of determination in IP v4 the source uses its own IP address and subnet mask along with the destination IP address. So as I mentioned before, the subnets are important. Play an important role here, and then IPv, six sources use the network address and prefix advertised by the local router. Local traffic is dumped out of the host interface to be handled by an intermediary device. Remote traffic is forwarded directly to the default gateway on the LAN. This is a very important concept for your exams and quizzes. So remember, both in IPv four and IPv six, the local traffic is dumped out of the host interface to be handled by the intermediary device, but however, the remote traffic is forwarded directly to the default gateway on the LAN default gateway, this is also a very important device in your networks, and it\'s very important that you understand what\'s a default gateway. A router or layer three switch can be a default gateway. Features of a default gateway or DGw include, it must have an IP address in the same range as the rest of the LAN. So if you have a 192168, 10.5 as a device, your default gateway should be around 191 6810, dot, something. So. So it should be one, most likely going to be 191, 6010, or one, for example. So it has to be in the same range of the rest of the land. It can accept data from the land, and is capable of forwarding traffic off of the land, so it can reach internet or some other land network that is not internal, internal. It can route to other networks. So those are the three things you must have in a default gateway. If a device has no default gateway or a bad default gateway, its traffic will not be able to leave the land. So this is very important. If a device has no default gateway, or a bad default gateway, that means you were given an incorrect default gateway. IP address or information to the that end device. It\'s traffic that end device traffic will not be able to leave the land, so to send the packet to host on the same network, host sends up messages to get Mac of the other host, and you can communicate using just the MAC address right. We learned that in our previous module, but to send a packet to a horse on a different network, it requires a default gateway. So what is going to do is the host gonna communicate with the default gateway and up to get the MAC address of the default gateway instead of the MAC address of the next host, because it doesn\'t know the MAC address of the next the host that that need to be communicated, right? So I\'m going to repeat that again. When the horse is sending a message to another horse within the same network, it can use the app to get the MAC address of that host in the same network and then just communicate. But however, when the host is trying to communicate to a remote host, a host that is not within their network, it\'s going to send the app request looking for the MAC address of the default gateway, and then the default gateway is responsible for communicating with that outside world. So the host must be given the IP address of the default gateway in order to communicate with the outside world. Gateway is a router must be on the same network as the host as I mentioned before, and the router know how to reach other networks. The router on your network is your gateway to other networks. So another way to remember this for your exams and to understand the concept the router on your network is your gateway to other networks, you know that is may not be internal. So a host routes to the default gateway. The host will know the default gateway or DGw, either statistically or through DSCP in IPv four, IPv six, sends the default gateway through a router solicitation or RS, or can be configured manually. A DGw or default gateway is that is static route, which will be a last resort route in the routing table. All device on the LAN will need the DGw of the router if the intent to send if they intend to send the traffic remotely, remember, on my previous slide I described explained this, so if the host is communicating within the internal network, they don\'t even need the router. They can send a packet from PC one to PC two without going through router. But if the host is trying to communicate to a remote network, it does. It does need the default gateway information so that it can send the packet to this port in the router, so it can use that information to communicate to the remote networks. So that\'s what it\'s saying here. HOST routing tables on Windows route print or net stat with dash r to display, you can display the routing tables so on a Windows machine, this is what a routing table look like. You can go and, you know, check it out on your own Windows computer, you can go net, stat, dash, R, and that will give you the routing table you have on your computer. Three sections display by these two routing commands, either nestad, dash r or route, print the interface list, IPv four routing and IPv six routing. The interface list is the all potential interfaces and MAC addresses, like, for example, you will have the network destination information and all the interface information associated with here. So that will be the interfaces right here. And you will see the default gateway, and you will have the network destination addresses and and those IPv four or IPv six addresses, and these two commands, the route, print and netstat dash, are some of the commands that you will be using as network administrators or network developers on the field to sometimes troubleshoot issues. But for now, for this particular course, you just need to know those commands exist and how to look them up, and we will go into depth of troubleshooting and advanced network configurations on our later lectures. Introduction to routing layer three. Router do not forward broadcast. Each interface is in a different broadcast domain. It learns path to other networks by exchanging information. The network layer provides services to direct packets to a destination host on another network and to travel to other networks, the packet must be processed by a router. The role of the router is set to select paths for the direct packet forward the destination host, in a process known as routing. So the role of the router is to select parts for the direct packet forward to the destination host in the process called routing. That\'s where the term routing come from, and each router the packet takes to reach the destination host is called a hop. So you will hear that these terms during these lectures and this course, things like routing next hop, hop and broadcast domain and this, this is where all of these, some of these terms come from. And again, don\'t worry too much about all of this information, but remember that we are covering this information, and you should have a bit at least a basic idea at this point. You know what this means. So that\'s the whole point of this particular slide. You can pause this video and quickly go over this if you would like to have a brief summary. And that\'s what this is. Router, packet forwarding decision, what happened when the router receives the frame from the host device? So you have a host device which is PC 10, sorry, PC one, which has the 190, 2.168, 10, dot 10. And what happened when the router received that frame right so the packet arrives on the router support. In this case, it\'s going to be the G, 000, interface, and then that R, 1d, encapsulate the layer two, Ethernet header and the trailer. Then the router one examine the destination IPv four address of the packet and searches for the best match IPv four routing table, and the router entry indicates that the packet is to be forwarded to router two. So this, this packet gets been sent through the switch to the router. But because the initial host have a have a default gateway associated with this right hand side of the sorry, left hand side of the r1 which has a 192168, 10 or one, the router one now is responsible for examining the destination I P v4 address for that packet, then it\'s going to search for that destination I P v4 address and look for the best match in its IPv four routing table. And then it\'s going to route based on that information. And then the router one, encapsulate the packet into a new Ethernet header and trailer and forward that packet to the next hop, which is going to be the router two, so the first hop is going to be here. So when the packet we was sent initially from the host, the first. Hop going to be here in right here in the router one, and then the next hop going to be the router two, because the router tune left hand side interface, which is 209, dot 160, 5.2. 100.226. Going to receive that packet. So you could actually look at this as like a this is your home router, and this is the router of a remote connection, for example. So that\'s what it\'s showing. And the routing table of r1 going to be, you\'re going to have bunch of IP addresses and associated next hop exit interfaces. And what they are doing in router. One is actually matching those route routing IP addresses, which with the next hop interface, and forwarding that to the next hop. So I know this can be a little bit confusing this particular slide, but just go over it one couple of times and you will understand what exactly been trying to mean I\'m trying to deliver here. So what, the, what? The key concept here is that when the packet arrives on the first router, it de encapsulate and look for the matching IPv four address in the routing table for forwarding for the next hop so that it can forward the packet to the next hop. So that\'s the very key, the key information you should get out of this slide. There are three types of routes in a routers routing table, directly connected remote and default route. The directly connected are routes that are automatically added by the router, provided the interface is active and has addressing so they are directly connected to the router itself, remote. These are the routes the router does not have a direct connection, and may be learned through either manually by a network administrator assigning static routes, for example, or dynamic, dynamically, which is by using a routing protocol to have the routers share their information with each other. Default route is for this is, this is forward all traffic to a specific direction when there is no match in the routing table. So when the packet arrives and you don\'t have any IP address associated within the router\'s routing table. It used a default route to forward all traffic to a specific direction when they don\'t know when the router doesn\'t know where the packet needs to be forwarded. So this is a very important thing that you should know. So in IP router routing table. We have three one is three major routes, directly connected, remote and default route. And you should also know the differences between each one of them and default route look like this on your Cisco router or Cisco devices, either it\'s a router or layer three switch. You\'ll be able to get default route information by typing show ip route, and you\'re going to come up with bunch of information. The some of the key things that you will be looking at is such as the static route. And then you will see in here the static route is the default. And then we have the static route set to this. This particular setup by just typing, show ip route. This is just to give you a quick overview of what it looked like on a Cisco device. And on the next slide, I will go a little bit in depth into this. But for now, because we are not doing a lab right now, you just need to know how to search it up the default routes. I will do a lab and post a video on my YouTube channel on a later day. But for now, just remember some basic information that you can get out of by typing show ip route command on your Cisco router. And the next slide I will look in. We will look into this a little bit depth, so you always read from left to right. So what we did here is we took this like this particular one line, and we\'re going to examine that in little bit in depth so that you will have a better idea when you are going to do your labs. So the O is a route learned by OSPF routing protocol. What is OSPF route? In protocol. You don\'t need to know right now, because you just get started working on learning about networks. This course is introduction to networks. But when we go move forward in our future lectures, we I will discuss and how OSPF works. But for now, all means in here is, it\'s, it\'s a route learn by OSPF routing protocol, 10.1, dot 1.0, which IP address shown here is the destination network address. And then you see this value within a bracket, 100 and slash two, where 110 is the administrative distance. So ad and how trustworthy that router path is. And the two is the metric, which is how far the network is. And then we have a IP address again, right after the we are here, and which is 192168, 200 226, which is the packet is passing to the next hop address. So this is the next hop address we have here. So this is the destination network address, and this is the next hop address. And then finally we have the Gigabit Ethernet 001, this 001, is the interface of the exit. So that\'s the exit interface. So concepts such as, What is OSPF and what is administrative distance, AD and, you know, trustworthy path and etc, all of these things I will go into depth in a different video, but just for now, just know how to read it from left to right if you were to run this show ip route command in your Cisco device. So if you route, if you type show ip route on a Cisco router, you get this information, and the static route is displayed with the S and the O here will give you the information about, for example, a OSPF routing protocol associated items, because Cisco follow the similar structure by knowing this basic information will help you in the future, because it\'s going to be the similar things, but slightly different as we advance in this course, static routing. Static route characteristics include the following. It must be configured manually. Must be adjusted manually by the administrator when there is a change in topology. So if you have a static route on a router and you decided to change your network, you had to remember to go back to that router and change their static route information. Otherwise it won\'t be able to automatically obtain because it is a manually configured item. Static routes always going to be a manually configured item if they are good for small or small and non redundancy, non redundant networks, like a home office or a small business with internal networks, often using conjunction with a dynamic routing protocol for configuring default routes. So you can use static routes along with the dynamic routing. And that\'s how most often you\'re gonna see it. You know, we probably never gonna see just a static route. You\'re probably gonna see static route along with some dynamic routing protocols. And on the right hand side, I just basically give you a basic idea of how static route and dynamic routes work. And I\'m not gonna go over this diagram. You can force this video and quickly go over it, if you would like to have a little bit of better visual diagram of how it works. But for now, for this course, for this particular module, what you need to remember is static cells are manually configured and typically used in conjunction with a dynamic routing. And if you change anything on your network and you have manually configured static routes within your network routers, you have to go back to those routers and manually reconfigure them, because static routes are almost always manually configured. They can\'t automatically, you know, change that when you change the network, dynamic routing. Dynamic routes automatically. Discover remote networks automatically, and it maintains up to date information and choose the best path to the destination. Find new best parts when there is a topology change dynamic routing can also share static default routes with the other routers. So what that means is basically, if you have dynamic routes and there are no static routes, we. Whenever you change your network configurations, you don\'t need to do anything to your routers. It will automatically discover the remote networks and maintain up to date information and choose the best path. But it also can find the best paths, when I say static, default route with the other routers by just communicating with them. So like, if this one has, like, router two has a static route, and the router one has dynamic routing, and if this router one gets exchanged or rebooted or change, it will actually knows this one has a static route, because this one has dynamic route, and it will be able to figure that information out. And on the right hand side, again, this is a diagram provided by Cisco. You can pause this video and read this information to understand what it is. Again, I\'m not going to go over it, just to save some time, and I\'m going to move on to the next slide, but however, I\'m going to highlight what\'s important to know in dynamic routing is that it is automatic. So that\'s the most key important thing that you should take out of this slide for your exams. There is a video on your Cisco NetAcad with the title IPv four router routing tables. That video explains the information in the IPv four routing table in depth, a little bit in depth than what we went over. And I will leave a link below in my YouTube channel for a copy of this video. In case you do not have access to Cisco NetAcad, either through registration with them, or through your academic institution. If you if you\'re studying this module for the first time, I would recommend pausing this video, checking that video, this clip first, and then coming back to continue this lecture. Introduction to an IP v4 routing table. We briefly look at an routing table before in our previous slide, so I\'m just going to go over a little bit more information with respect to that routing table, but not more so because this is going to be the last slide that we\'re going to look at this particular concept, but in the future modules, I will come back to this concept. So this is the last briefly introduction, introducing. What does this show ip route command will get you? So the show ip route command shows the following route sources, l, right here is the directly connected local interface, IP address. C, right here is the directly connected network, s, as we went over before, which is the static route, which was manually configured by an administrator right here, or which we have went over, which describe the OSPF and the D will we will be describing the E, I, G, R, P, protocols for now, as I mentioned before, you don\'t need to know what is OSPF and EIGRP, what are their differences and how you configure them. But just for now, what you or you should know is by typing show ip route, you might see these letters on the left hand side, and what these letters means. You can just look at this slide, and you will know what they means. As you work through your Cisco carrier and you work through the Cisco NetAcad modules, you will familiar with this. What did they exactly mean to the point that it will be in your back of your mind, like it will be like, you know, it\'s like, will be a second nature. You don\'t even need this slide to know what S stands for. For example, this command shows types of routes, such as, you know, directly connected, such as CNL, remote routes, D, O, etc, and the default route, which is S star. So this is just a brief introduction to IP v4 routing table, as I mentioned before, again and again and again, when you do these labs, which I will be posting on my YouTube channel later. You will get used to seeing these letters and routing tables, and you don\'t even need to come back to this slide, you will remember like back of your hand. So that brings us to the end of this lecture, and we will go over quickly. What did we learn in this module? We learned that the IP is connectionless best effort and media independent. IP does not guaranteed packet delivery. IPv, four packet header consists of fields containing information about the packet. IPv. Six overcomes IPv four, lack of end to end connectivity and increased network complexity. A device will determine if a destination itself, another local host and a remote host like it can determine, you know, the destination going to be itself or another host or a remote host. Default Gateway is router that is part of the LAN and will be used as a door to other networks. The routing table contains a list of all known network addresses, like prefixes and where to forward those packets. The router uses longer subnet mask or prefix match, the routing table has three types of Route entries. They are directly connected networks, remote networks and default routes. So those are the key concepts that we learn in this particular module, and one of the key things I would like to emphasize, even though the Cisco exams may not be highlighting this, is you should know the difference such between IPv four header and IPv six header, and how they are slightly different from each other. And you know why we are using IPv six now, as opposed to just keep using IPv four, because we ran out of IP addresses in IPv four, right? So remember that. So those are very key important concepts. That\'s everything for today for this particular lecture. If you have any questions or concerns related to this module, or anything related to Cisco NetAcad, introduction to network series. You\'re more than welcome to leave a comment below, and I will do my best to get back to you and answer all your questions and make sure you go over all the covered topics and items before you take your quiz or exams, because I may have skipped through some of these things. I may have gone through too fast. So you can replay the video and go back to those slides, especially the important slides that you can pause and read those information make sure that you understand those concepts so that you will get a very high score on your exams. Please make sure to thumbs up and to this video and subscribe to my channel Until next time. Have a nice day.