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Networking Basics

12. Routing Concepts Part 2

Now, let's talk about more routing. First, I'm going to add two routers. In our topology, I have router one and a router to here. Here, I'm going to connect them together. So this is point-to-point connectivity. And I'm also going to use a network that is designed for a point-to-point network as well, namely, 2168. And the third option that I'm going to useis reference to router ID one and two. So I will use twelve one and 20, andI will use 30 for point to point networks. I'm going to assign one for my router and two for my router to both. I will be using an E-Zero interface. Router One and Router Two Router One also has another interface that is connected to another network, which is 100 dot one, dot zero, slash 24. There you go. Our current goal is to build a R two Centrafa 2100-10 network. Of course, we know that router Oneand two can communicate to each other. Assuming everything is properly configured, the port is set to the correct speed and duplex. Assuming everything is properly configured and set, routerTwo can send traffic to one, nine, 2168, and twelve, which is routerOne's easier interface. How about router two to this network? Let's check. Router Two's routing table would look like this. I have two networks. One of them is 192, 160, and 812 00:30. And this is via E zero.I have another network. Oh, no more networks; there is only one. So therefore, router 2 cannot, by default, send traffic to 10. How about the router one? Let's check its routing table. So this is router one's routing table. Let me just name it a routing table. And under R 1, you'll notice a 192, 160, and 812 00:35 ezero. The same as we have in Router 2. We also have here in Router One's routing table 100. This is connected to EONE. Let me just add it here: one. All right. Now both of these network on ROne's routing table is directly connected. So, as with router two, I'll use a code of C. Sprocket table. Again, we haven't completed our main goal. The main goal is for R to be two-centrafaced to the 100-10 network. By default, there is no routing. Well, the only routes we have are those that are directly connected outside of the directly connected network learned by routers. Routing is disabled. So what we're going to do now is introduce you to static routing, the manual way of adding a route that is configured in our routers. In a router source perspective, I will add a single line of configuration, and it really depends on which vendor or which device. But it's something like this IP route, or route to 100 dot one, dot zero, slash 24. Sometimes, we use that map. So in this case, two for five, dot zero, and lastly, we need to add the next hub IP address, which in this case is 19216-8160812-1, which is the router's one IP address. Now, this is a static route. Assuming this is all correct, it has been successfully added to our router, which is router two. It will add Route 100 to our routing table a new route 100.This is via e-zero as well. Now, what's going to happen here is that if the router two sends traffic to ten dot zero, dot one, dot zero, it will just forward the traffic to router 1, and router 1 will forward the traffic to the ten dot 10 network. Now we will add more routers to our network. I will add three routers so they can be connected to a switch here. So all three routers—routers two, three, and four—are connected to a switch. And they will be using one network. The network will be 192 168, and the third octet is referenced on the router IDs, which are two, three, and 400:24. This will be dot two, dot three, and dot four. They will all use e one interfaces, ethernet one, ethernetone four, R two, R three and R four. Also, all three routers will have another network, which is the ten dot zero, and the third off that will be the router ID. The router ID is three. For router four, this is ten three, dot zero, and slash 24. This is four. by the way. On the network, this will be 100, 40, and 24. Now for router two, let me just erase this line. Okay, I'm going to add 100 to 200:24. So we have three routers, routertwo, router three, router four. And the goal is for all of this network—this network, this network, and this network—to be able to communicate with each other. So, if I have a PC on the 10/40 network, it can communicate with the server behind R/3 on the 10/30 network. Now, if you check the routing table in myrouter too, you will see a new directly connected network, which is 192 168, dot 2340, slash 24. And this is via e one. Let me also add the interface for the three networks connecting to the 10 3 40 network, e 2. This is e two, and this is e two as well. Right? There you go. Under router two, we have another network, which is 100 200:24 via Et. And again, this is directly connected. So you will use the code C for R 3 and R 4. Let us just add it here. Very simple. All right. We will add C here: one, nine, 2168, dot two, three, and four via e one. Now let us expand. All right, okay, we'll do it as simple as this. We also have a directly connected network of ten dot zero, three dot zero, and e two, and we have 100 40 and e 2. All right, here's the problem with static routing. If we use static routing on all three routers, Router two, router three, and router four That means we will be adding two lines for each router. Because on router two's perspective, I willadd this network and this network. So two networks are in Router 2. The same is for RF three. We will add this network and this network. So there are two lines and two networks per router, which is not bad. We only have three routers anyway. The problem is, if we have too many routers running in our network environment, can you imagine if we have 50 or even 100 routers? That means that if I have a router and want to communicate with all networks behind all 99 routers, I'll have to add 99 static network configurations to each router. So that is too heavy. That is too complicated when it comes to configuration. Another reason why static routing is not that good is when there are changes occurred.For example, what if, for some reason, your colleagues or your manager decide to change this network? It's no longer running 10 40 or 10 40; it's now running a new network configuration. It's now ten 00:400.See, the third object changed. It's now 40. What will happen if we add it statically? For example, I add 100 to 400:24. What happens if I add it statically and this has changed? You will never reach the ten 00:400. Because what is configured here is manual, it will not change itself automatically. Another reason static routes are not always preferred is that if there is a downtime, such as this network suddenly going down, it is completely gone. The 10/30 network is unreachable. If I enter 100 here, it will be saved in R 2's routing table. Okay, this network is down. It's not recognised even by R three.Well, it is recognised now, but from the perspective of two, it will still send traffic to this network. Why? Because you add it manually, it will not be removed automatically. Now, I'm going to introduce another type of routing. This is what we call dynamic routing. This allows us to learn many different networks in less time. Not only that, it adapts to changes. Okay, so if there's a network down, or if there are changes in the network, this will also be automatically changed in our local router's routing table. So how does it work? Well, first, what I'm going to do is enable the dynamic routing protocol. Okay, what are the dynamic routing protocols? Well, the most popular is SPF. We also have BGP. However, BGP is more commonly used in a large-scale, or should I say one-scale, environment. We also have proprietary or vendor-specific dynamic routing protocols. We're not going to use that. We're going to do this as simply as possible. So we're just going to use OSPF. We have to enable it. First, we need to know what networks will be advertised. So in the perspective of R2, this is our R2 dynamic routing protocol. We need to advertise the ten dot zero dot two dot zero slash 24. Okay, what else? Well, that's the only networkI want to advertise anyway. And lastly, we need to alsoconfigure this network here, this network. Because this is the network that Router Two will use to initiate convergence with Router Three and Router Four. So I'm going to also add 192, 106, 823-4024, and again, enable OSPF, which is the dynamic routing protocol. Add the network that you want to advertise on. Also add the network that will be participating in the routing convergence. So Router Two will set up dynamic routing to R Three and R Four as soon as they have established that they are now neighbors. Okay? So R two is now OSPF neighbour to R three and r four. What it will do next is advertise this network. So it will advertise 100 two, RThree, and also two R Four. So you will see here on both R Three and R Four's routing table that 100 20 via E One is learned using a code of O for OSPF. 100 20 via e one. There you go. Now we will do the same process for R Three and R Four. So, from the perspective of R 3, it will also learn 100 and 40 by E One code is "zero," and the perspective is R four." It will learn 100 30 by E One code one. There This is router three. and this is router four. This is Router One, which is used in our previous example. And this is Router 2. Now, for the router to routing table, we already have it in our static configuration example, but all we need to do is change it to not see, sorry, there you go. So, assuming Router Three and Router Four advertise these networks correctly, Router Two will learn about them via We SPF. So that's it. We have completely enabled the dynamic routing protocol, and we have shared the Ten 020-3040 network from N to Router Two. Router Three, Router Four Now, the good thing about these dynamic routing protocols is that, say, there is a change in R for network. So instead of 100:40, they change it to Ten 00:400.What will happen on Routers Two'sperspective in its routing table? This will be updated. There's a change. All right, we'll change it to the 10:400 network. Now, if Router Three's network is down, it's totally gone. What will happen is that on Router 2's routing table, we will delete this. It will be removed because updates froma dynamic routing protocol is automated.

13. Routing Concepts Part 3

Interveal and routing Now, the interval and routing or interrupt communications allow hosts from one VLAN to communicate with another VLAN. We have here a network that we used in our previous discussion. At 00:24, we have VLAN 10 with a network of 192 168 10. At 20 00:24, we also have 192, 168. Now, the requirement to enable interconnection and routing is a layer-three device. Many people believe it's a router, not just a router. Other layer-three devices could also be involved. We have three options or examples. The first one would be very interesting because this is almost the same as what we talked about in our switching discussion. But this time, instead of adding an uplink switch, we're just going to add an uplink router. Let me just move this further down like this, okay? And I'm going to use this interface, let's call it E 10 and E 11. Now I'm going to use E ten for a specific VLAN. This E-ten port is also part of VLAN ten. Now, I'm also going to add another uplink, and this time I will use the Eleventh Switch Interface. Okay? So as you can see, we have two dedicated interfaces connected to the router. Now on the router, this is a route port with an IP address of 254. OK? This is 192 168 ten, 254. The other interface is also part of VLAN 20 with an IP address of 1254. Now, all of this host's computers must have a default gateway of not 2 5 4 Okay? The default gateway is 2 5 4. I will also set it here: full gateway two five four, default gateway two five four. Now, the concept is very simple. If PCA wants to reach server D, all it needs to do is send the traffic to the full gateway. And this will be automated because PCA is from the 102-168-100 network and he's trying to reach a destination server or a destination host on another network. Of course, it will use or redirect the traffic to the full gateway. Now, the router here obviously has a routing table, okay? If we look at its routing table, it looks like we have two networks. One network is obviously 192, 168, dot ten, dot zero, slash 24, and it is learned. Let's say this is e zero; this is e 192, one GC at ten, 00:24 network is learned from e zero. And this is obviously a directly connected network. We also have another network lesson, 192-16820, slash 24. And this time, this is another directly connected network as well. Now, when the router does the process, which includes checking its routing table, it will say, "Hey, your destination IP address is part of this network: 192, 168,200," which I learned from e one.So I will forward the traffic to one. Now, there is another example. This time we will use the same router but a different connection. Why is that? Because this example may be a waste of ports, especially if your switch has many VLANs configured. What I will do is use only one interface, and even if I create multiple VLANs on the switch, I will still carry all of these VLANs to this interface. Take note that because we are carrying multiple VLANs in this switch interface, we will use the 802.1Q protocol, also known as taginterface. Now the question is, what's in the router? We already discussed the concept of 8021-TWO, or the tag interface. But on the router's perspective, how is it possible to forward traffic to multiple networks through a single physical interface? Well, this is the concept of subinterfaces From zero, we can create subinterfaces. Now, it really depends on devices or layer-three appliances, but other vendors use this concept. Okay, subinterface. You name a subinterface and configure an encapsulation-decapsulation idea, which is also the VLAN ID where you want to use a default gateway. So I'll make my subinterface e-10 encapsulate blank 10. Also, I will add an IP address. This will be one nine 2168. I'll just use this caller, ID 2106810-2542, and I will create another subinterface. This will be e zero dot 20, and I will use VLAN 20 for encapsulation and decapsulation of layer 2 timeframe. I will also add an IP address, which is 192 168 22 5424. So what happens here? Well, in the router routing table, it will still learn that these two networks are directly connected. but this time the interface will be different. It's using one physical interface, but it has created some interfaces. This is e zero dot ten and e zero dot twenty. OK, the process is the same: PCA send traffic to the default gateway, but this time it is specific to e0 dot ten because e0 dot ten is where we configure 192-16-8254. It will check the routing table, and it will forward it out to the subinterface. E 20 will be carried on this single interface because it is an eight-two-one Q link. Anyway, for the final example, we will not use any external Layer 3 devices. So I am going to simply erase all of these, right? I will use this device, is itnot a layer to device only? So therefore, we cannot route traffic, or we cannot do interviews and routing. Well, if you're talking about a layer-two device, yes, but some switches have layer-three capabilities, meaning they understand routing. It also has a routing table. Is it possible? Yes. And the concept behind this is to create a layer-three interface for VLAN. Okay? Many vendors and many appliances do it differently, but the concept is the same. We have VLAN ten and VLAN 20. All we need to do is create a logical interface for both VLANs and assign an IP address. This time I'm going to assign one nine2168 ten 254 24 four VLAN ten interface. I'm also going to assign 192 168 2254 for my VLAN 20 interface. Now, in our example, I will just delete this. In our example where PCA wants to send traffic to server D, it will send it to the default gateway. The default gateway exists in our three-layer or multilayer switch. Okay? The two five four assist here. Now, if we look at the routing table, you will see this interface VLAN 10 and an interface VLAN 20. So the VLAN I will always say it has its own interface and an IP address. So therefore, if we send traffic to another VLAN or to another network, the switch will take it and it will route it. So from 192 168 10: 254, it will send it out to 192 168 22: 54 and forward it to the destination server Peek with an IP address of 1 168 24. This is a very common setup. As a matter of fact, the most common setup among the three examples

14. Routing Concepts Part 4

IP Header or IP Version 4 Packet Header It operates in layer three of the OSI. Then it encapsulates the fourth layer four.It will hand over its session to the application and send data traffic as it creates it. Now, for the IP header, I have my own version, so I will draw it something like this. We have the destination and the source address. And just above the source address, we have these fields. We have the TTL, and this is what we're going to discuss later. We also have the protocol, and we have the header checksum. Now, the header checksum is used to identify if there is a corruption in our IP header. So I'll just put here "identify corruption." Now, above TTL and protocol in header checksum, we have the fragment and the flag. Now fragment. This allows the IP to do fragmentation, and if it's reached the source, it will do reassembly. Now, this flag over here tells or identifies if fragmentation is required by the packet. Okay? So this is just a yes-or-no flag. All right. Now, TTL, as I mentioned, will be discussed in the next couple of videos. The important part here is the protocol, okay? Protocol. This allows our packet to encapsulate on the next layer. And it's very common that we use TCP and UDP as the protocols. All right. Now, we also use the source and destination addresses to identify the source host IP and the destination host IP address. Take note, this is the IP header. This is the IP used by the IP protocol. Okay? IP as a protocol is unreliable and doesn't guarantee delivery. It does not also perform error checking or manage the messaging queue; it lacks functionality. Now, it is very important to notify the sender if there are network problems. Now, to verify reachability or connectivity from the source to the destination, we use a specific protocol. and this is ICMP. or the Internet Control Messaging Protocol. Now, ICMP, in order for us to use this, will be added to our protocol field here. So we're not going to use TCP or UDP. We will use ICMP. And maybe you're thinking, okay, this protocol is not dedicated to layer-four protocols. No, no. And ICMP is still considered layer three because this is not used to exchange data between systems. Okay? So it's not layer four, but a layer three protocol. Now, ICMP has three important fields—three fields. These are the eight-bit which is eight bit.We have the code and the checksum. The type field has eight bits with values ranging from 0 to 2. Five, five. Take note that only a few ITMP types are valid. As a matter of fact, type 44 to type 252 are marked and used. This is additional context from the type for the field code. For example, I have ICAMP types three and eight. Now, the ICMP type 8 has only one code, and that is code 0. Well, ICMP type 3 has a code ranging from zero to 15. Now the field checksum allows us to add additional error checking apart from the header checksum of our IP header. Okay, now what I will do next is I'm going to add PCA, and in between PCA and the server, I'm going to add a router here. Now we're going to provide some of the examples that ICMP type provides that are some of the most useful and commonly used examples of ICMP type. Okay, so I have here ICMP typeeight or also known as echo request. This enables our source, say the Apia. There are 170, 2160 to send to the destination and 109, 21680 here. Now assuming that it can reach the destination andthe destination can reply back to the source, itwill respond with an echo reply type zero. Okay? Assuming both are successful, this is considered a successful ping request and reply. An additional ICMP type that is also very common is when the server cannot be reached. This is referred to as ICMP type 8, or destination unreachable. So what happens is that the PCA here sends an echo request, but for some reason this router cannot reach the server. It will send back "destination unreachable," which is again type 3. Now we were going to add additional code because there are a few reasons why the server or the destination cannot be reached. And one of the most common codes is zero. This means the network is unreachable. Okay? So for some reason the server or the router cannot see this network, so it will reply back to PCA. I cannot see the network, so the code will be zero or network unreachable. Now we also have a code 1, which means the network can be reached or some of the hosts under that network can be found. But for this specific IP address, okay, it's not reachable. So we have the ICMP destination unreachable type three, code one, host unreachable. Now, as I mentioned, we have multiple codes from zero to 15 under ICMP type 3, destination unreachable. Okay, we're not going to provide examples of all of the codes, but one of the most common codes that is being seen when we're troubleshooting is code number four, which is also known as fragmentation required. Okay, now this is the three, I would saythe top three most commonly seen ICMP type. But there are also ICMP type that very common as well. One of these is ICMP type number 4, which is also known as source quench. and this is to notify the sender that the router is congested or highly congested. So we're sending a message to the source to slow down. Okay, we also have ICMP type 5, which is also known as redirect. The message is: Instead of me, use this router instead. and this is used for route redirection. For example, the original router doesn't have an available route to the destination. So it's telling the source, Hey, I'm not available. Can you please use this route instead? And as I mentioned, this is used for redirection. We also have ICMP type 11, which is also known as time exceeded. Now, time has expired. This is more commonly used when we use TT to yell or time to leave. Okay, and we're going to discuss that in a bit because.