Cisco CCIE Enterprise 350-401 Topic: Infrastructure Part 3
December 13, 2022

18. OSPF Network Types Metric Passive-interface Theory

I’ll talk about COVIDOSPF network type metrics and passive interfaces in this session. And the lab will be completed in the following section. If you go and check the slabs, So let me quickly show you the slabs in the slaves. You’ll find that in three you have to learn about OSPF and you have to compare it with EIGRP. So, for that, I’m going to go over COVID and EIGRP in different video series. So once we know OSPF and once we know EIGR, it’s easy to compare.

Then in three, two, and B, you can see that we have to learn and understand more about OSPF. And that’s what we are doing at this point in time. So, let’s quickly go over the OSPFnetwork network type and the utility of the passive interface. Now, OSPF supports a wide variety of network types. Here you can see that in OSPF you have all these different types of network support. Now, how do you memorise this because, as you can see, it’s a big number? So consider this: you have point to point, and you have seen it here. So there’s point-to-point, point-to-multipoint broadcast, and non-broadcast. As you might expect, you have network type broadcast and network type non broadcast. And then again, if we add point-to-point and point-to-multipoint, So, obviously, we now know that point to point is just a point to point network. Two devices are connecting with each other. It’s a point-to-point network. Then what about 2 multipoint? As you can see, this is a non-broadcast point to multipoint connection.

So you can think that you have Okay, two multi-point broadcasts and one non-broadcast? So that means you have one, then two, and three. Apart from that, you have network-type broadcasts. So there are two types of networks: broadcast and non-broadcast. That means you have to have five different types of network support. Again, if you go back and look at the nature of the broadcast and non-broadcast, So if it is a broadcast, that means the DrVDR selection will happen and the neighbour will form automatically. That means you don’t have to write the manual command to form the neighbour relationship, correct? However, if it is a non-broadcast and Dr BDR is forming, it is clear that the hello is a unicast multi-list. When you’re seeing unicast, that means you have to go and use the neighbour command. So you have to manually form the neighbor, correct? So once we know about the broadcast and nonbroadcast, you can see the timer as well. Correctly, it is 10 and 40 seconds for the broadcast network and 31 and 0 seconds for the non-broadcast network. We can apply the same concept here. As you can see, the point to multi-point relationship exists. You can think this is a point-to-multipoint broadcast.

So that’s why it’s multicast. Hello. They will not form the Dr Radiat because, once again, it is point to point, and there are so many points to points to multiply that it is possible to think in that manner. Because there are only two devices in a point-to-point network, you will not form the Drvdr; however, you will form the Drvdr whenever points to a multi-point non-broadcast network. Now, this is not broadcast, so that’s why you have to go and use the neighbour command to form the OSPF neighbour relationship. That’s the whole summary we have for the OSPF network type. So let me go back to the theory. Here, you can see that it’s a broadcast, so it will do Dr. VDR selection. Then it is using these multicast addresses because this is broadcast; they will not form the neighborship manually; automatically, they will form point-to-point. There is no need to define the neighbours because you have only two ends. They will form a neighbourly relationship. Their time will range from 10 to 40 seconds. They will use the multicast status, but will also point to multiply. Everything that is valid here for point-to-point will be valid for point-to-multipoint as well. Okay now then we have nonbroadcast. Whenever we are talking about nonbroadcast, then you have to go and form the neighbour relationship manually.

OSPF will elect Dr and BDR, but neighbour relationships will be manual, and that’s why we have this summary. This summary is simple to remember; there is no need to recall it, but it will demonstrate that we have a point-to-point network, a point-to-multipoint network, a point-to-multipoint broadcast network, and a broadcast and non-broadcast network. How are we going to do the configuration? The configuration part is actually very easy. Only one command is there to define the network, and you have to go to the interface because you are over the serial interface. You go to the interface and use this command. IP OSPF Network Suppose if you go and type “question mark,” then you’ll get all the options. So is it a broadcast? Is it non-broadcast, point-to-point, or multi-point? You will be given each of these options, and if it is using unicast methods, you must define the neighbor; if it is a nonbroadcast, you must define the neighbor. Otherwise, the rest of the configurations are standard OSPF configurations. So for example, NBM stands for “non-broadcast multi-access,” so here we are going and defining the network type as “point to multi-point,” and if it is a non-broadcast, then you have to go and define the neighbor. So just remember this summary, and things will become easier. Now OSPF is using cost as a metric. Here, you can see the speed and the cost. So, for example, your cost for fast ethernet and ape will be one, and then you can see photo ethernet for token ring for MPs, and so on. Now, the lower the number, the better. So if the lowest cost is there, that will be the preferred path in the route selection. how we are going to do the basic OSP configuration, although we have done one lab.

So there you have seen that you can go and initiate the OSP process; you can define the router ID; otherwise, it will take the highest loopback or highest physical interface. If it is not configured, you can define the area and that’s it. So this is the baseline configuration. The intriguing part is that we are now defining the wildcard bit. It is now recommended that if you know the exact subnet, you can use the exact wild card as well. So, if I’m using point-to-point networks, I can use, say, 173-21610, which is 172-1710 in this case, and then I can use wildcard. So like that, we can go and use the wild card wisely. What will happen if you go and initiate the OSP process? Once we start advertising the network, or once you put this network command, they will send the hello packet, and the new relationship will start working. We are aware that your steps in the two-way excess begin exchanging loads into full. First, they will form the neighbour table and the deposit table, and finally, they will run the SPF algorithm, and we’ll get the final OSPF routing table. Right? Now the final thing here in this recording is the theory of passive interfaces, the concept of passive interfaces. Assume that if you do not want to form an OSPF relationship, you can make any of these interfaces passive. So, if I make this interface passive, you’ll notice that the command prevents updates from being sent or received from this interface.

In this example, it is showing this interface. If you go and make this particular interface a passive, or any interface a passive, they will not participate in OSPF; a neighbour relationship means they will not send or receive the updates, and that’s the usefulness of a passive interface. But, in general, we will use this command to do this; no passive interface is zero here; as you can see, we will first make all the interfaces passive. So the command line is set to passive interface by default. Suppose if you have ten interfaces, that means on all ten interfaces you’re not sending and receiving the updates, and then you will go and add the interfaces one by one where you want to send or receive the updates. We have one important note here: the passiveinterface command will prevent OSPF and EI CRP from forming neighbour relationships out of that interface. No routing updates are passed in either direction. So this passive interface is true not only for OSP but also for EIGRP as well.So we are going to stop here. And in the next section, I will show you a few of the things that we have studied here. Like network type, you can go and change the network type, and you can enable the passive interface.

19. OSPF Network Types Metric Passive-interface Lab

Let us do the lab here so you can see the topology. We have three routers and one switch. As the L-2 switch, I’m using in-between switch 10-5. So that means I have area zero. So this big blue circle is area zero, and the network is ten one. You have switches 10 one and 10 two connected that are inside area two zero twenty, and the network is ten one and two. I have already assigned the IP address. So what we’ll do is go and enable the OSPF process. Then we’ll go and check the default network type, and then I will make any of the interfaces passive interfaces inside areas, and then again we’ll verify the OSPF neighbour relationship. So let’s do this: I can go to the router OSPFone, and even if we’re here, we can run this script. So, if you’re configuring over an empty party, you have this script option, say Conft router OSPF 1, and you can advertise the network as well. I can select the devices, and then I can send the script. Now once OSPF is configured, I should go and assign the network, or I should advertise the network. I can use the network command.

So, go ahead and check the IP route, your connected interface, and in the network command, you can actually use it with the wildcard bit, and we should check that this 10 of area 0 is part of it, so we know as per hour to policy that this is correct. Then we have one loop back here that will be stepping in the area where you want to put this. Also, I’ll put it inside area zero, and then I have one more network, which is this guy here connected to area 20 network command. Likewise, I can go to switch number two and check the connected routes. I can use my network command. First of all, I’ll advertise my loop back inside area 20, and then I’ll have my network that is connected, which is inside area 20, because the bottom switch is actually everything inside area 20. So that’s why area 20, area 20. So, when we run this account, you’ll notice that both interfaces are now part of area 20 and will run the OSPF, and we can see that the OSPF loading to full indicates that all states have been completed. So I can go check the show IPOs PF neighbour you can see the full BDR as well as the interface. Then we can check IPOs through the PF route. OSPF So here, you can see that you have the metric value and you have the ad value. The ad is one, and the matic is ten plus one, so that’s why it is eleven. We know that for the ethernet interface, that is one, and the other is for loopback, so that’s why it is showing like this. All right here, you can see the Ethernet. So we have ten for that, and only one is used for the back, all right. The next thing that I want to check here is your IPOSPS interface, and that is here where you can see that interface where the network type is broadcast. So I can connect the switch via Ethernet 0; they can connect to the interface, and I can make that IP PF network point to point.

Now you can see that you have broadcast nonbroadcast multipoint to point, and if you go to point to multipoint and type question mark, you will have point to multipoint by default, which will be broadcast, and then you will have the nonbroadcast. So I’m interested in making this point to point, and both sides should be done in this manner, so the other side is also point to point. Now you can see that again. The OSPF process is running, it is going from full to down, and the SPF algorithm is running one more time. From there, we have a new routing update or routing table showing IP or SPF, and the interface is Eagle’s network, which is now point-to-point. You can see this cost as well. There is other information as well related to timers, known stock forwarding, et cetera. All right, so we have completed this task with these two switches here. Likewise, I will go and initiate the OSPF process, and I will advertise the network for R1, R2, and only R1 and R two.R3 is not available. All right, so let me quickly check here in switch 10 one.What is the complete OSPF configuration that we have completed? So of these three networks, one belongs to the network that we have connected with r1 and R Two.That is nothing but area zero. And then these guys have one loop address. Likewise. I’ll go ahead. And then I’ll use two to two areas, and then if I go ahead and check show Ipospf network here, we have three devices forming the OSP of relation if I go ahead and check Ipospf interface, basically I want to check the interface. So, once again, I see that the network type is broadcast. Now in our topology, either I can use network type as a point-to-point or Wordcast, but we have seen that chart that shows that as per the topology, if you are working with frame rates, then you can use NBM, and then you have the mode for NBM. I don’t want to make this a non-broadcast if you do, so suppose I go to R one and R two and I should know what is my neighbor’s show IPOs PF neighbor.

And if I go to interface zero and make this IPO’s PF network non-broadcast, then I need to add the neighbour command manually. So now, if you check with your neighbor, you can say it’s a down. In this case, you have to use this neighbour command. You have to go to router one and use the neighbour command. Who is your neighbor? So if this guy is your neighbor, then use the neighbour command; this guy is your neighbor. So manually, we are adding the neighbour now. It is also detached here. So these are my neighbors. I’ll go to the iPOST network’s non-broadcast interface e0, then to router us PF-1 and add the neighbour to this. And again, I’ll go and add one more neighbor. Then you can go and check your IPOs on the PF neighbour interface, and then it will become non-broadcast. However, we can see that the network is down because we are using the incorrect type of network; if we have the NBM type or a nonvertforce type of network, we should go and use it again, as you can see by the hello and the changing time. Okay, so I’ll go ahead and make these backup interfaces and IPOs for the ASPF network, which is for example broadcast. So one side is broadcast, and the other side is not broadcast at this point in time. And now you can see it is forming a relationship with the switch number 10 one.

So if I go and check the “show IPOsPF number,” you can see it is forming this. Likewise, I’ll go ahead and again interface the IPOS network, which is broadcast, and then we can go and check the show IPOs PF neighbor. Alright, so now we have to test the final piece, which is the passive interface. So, let’s go ahead and make one of the interfaces over R one as a passive. Once you see that we have this command passive interface default, I can route to OSPF, and you can make no passive interface. So once you do this command, all the interfaces become passive, which means your neighbour is down. So here you have to use a passive interface, and that is the “e zero zero.” I want to avoid any passive interface. If you go to check on your neighbor, So you can see that this is up. So that was a lab related to whatever we studied in the previous recording. You can refer to this particular lab.

20. OSPF Authentication & Virtual Link Theory

Next, we have OSP for authentication and a virtual link. So start with OTP for authentication. Now, actually, it’s very easy to configure, and it’s different than RIP and EIGRP. What we can do, first of all, is go to the area. So you can see that I’m over OSPF, in the minside area, and using area zero authentication. Then I can go to the interface level, and then I can go and give the authentication key. So we have two things: we have the plaintext, or clear text, and then we have MDF. Now, in the same way, we can go and configure the MD-5 as well. So again, you have to go to Area 0. Here you can see that I’m over area zero, and the authentication message is then. I will go to the interface, and then I can assign the message. I just saw. So it’s very easy and straightforward. I’m going to show you in the lab section about the message digest key for this authentication, so we can discuss more in the lab. The next thing here is: what about a virtual link? Virtual linking is again one of the use cases we have in OSPF. For example, due to any reason, the customer network is not able to directly connect with area zero. We know that all the areas should be connected to area zero.

Assume you have Areas 1, 2, and 3 available. Later, for some reason, you are connecting area four with area three, not with area zero. So in that case, we can create the tunnel in between area zero and area four. So the router inside area four will think that I am part of area zero or that I am directly connected to area zero, and that’s the concept of a virtual link. Again, you will see the configuration, and it will appear that we are constructing the tunnel. So router, area one is working as a transit, and then I have a tunnel in between, say, area zero and another area. So let me go back here. So here you can see this is a classical example—that you have area zero, area one, and area two—and then you’re creating the virtual link in between those. Okay. Now there is a possibility that you may have area zero, and in between you have area one, so once again the possibility is less. But still, you can create a virtual link between them. Once we’ve created the virtual link, we’ll place the message over area zero, using the same key we used to create the virtual link. So we have seen all these shifts, and let’s perform the same task in the lab setup so we’ll understand more about the authentication and the virtual link.

21. OSPF Authentication & Virtual Link Lab

Let us carry out the authentication virtual link lab. I have made the change to my setup. Here, you can see that. R1, R2, and R2 are now available. But switch 10 five, then switch 10 one, and then switch 10 two. So I flipped one switch, then another, and then another at the bottom of the subsequent network IP addresses that I had changed. So we have network ten, 1110, 1210, 1300, and then we have respective areas like area zero, area one, and area two. Now in lab number one, we’ll go and create or run the OSPF in area zero.

And then we’ll do the MD5 authentication in the same lab. Later on, we have to create the virtual link, and we have to make Area 1 a transit. All right, so let me show you this IP address assignment. Here you can see that we have created and assigned IP addresses only so far, as per the diagram. These are the IP address assignments for R1, R2, and all switches. So now let’s start with area zero, that is, R 1, and switch 10 five.I’ll go ahead and enable the OSPF router. Then I’ll have network number one, for example, and put this inside area zero. So let me do that. Then I’ve got network 10, 1, 10. Also, I’ll put this inside area zero. All right. Now we’ll go to the switch, which is switch 105, and we can go and check the network. First of all, we’ll go and initiate the OSP process. Then there’s one network that’s 10 1 10. But we have a 10510-five network as well. So let me quickly do that. For example, we have the rest of the network. So now you can see that I have enabled this or that I ran this command. But still, I can’t see that OSPF is up and running. So I should go and check the IP address, and we should have this IP reachability. So E here is correct if I go and check the interface configuration for this switch. So let me try to check. So we have this command configured, and the protocol is up. So if I do the ping, let me do the ping from here; that’s the router’s IP, and I can see that the ping is working. If we could go check showIPOs PF neighbours show run section OSPF, that would be great. So here you can see that I have this network inside Zillow.

And then I have my network at Salooback. But still, I can see that they are not forming a neighbourly relationship. So now I’m going to go here and give this network a 10 1 10. And then I’ll remove this network statement. You can see that the issue here is that we have two entries; I’ll go back and delete one and add another. So let me try to do both in router number one at the same time. Okay, let’s try to check the IP and USB numbers. Now they have two options for getting to another state; they are stuck in another state. Alright. And if I check in here because we haven’t removed OSPF yet, it will show IPOs PF neighbor. Okay, so maybe it’s now up because the network type hasn’t changed, but it’s now showing that it’s up and running. So that’s okay. The OSPF relationship is now established over area zero. What I want to do now is run the authentication so I can go to router OSPF 1 and then area 0 authentication. Here, you can see that you can do plain text. If you want, you can leave with this authentication, or if you want to do the MD5 that is more secure, then you can go and use this. You can see that the neighbour is now up now that I’ve done this. But there is one issue with the authentication key: it does not have any valid keys. So now what I will do is go to “zero zero” and then “Iposp” for authentication. You can see that you have authentication and message digest options.

So I can go and add the key as a CCNP. You can see here that you can go to authentication and key, and then you can see here that you have the option of going unencrypted. This is not what I’m looking for. So I can go and give the message digest, but I want to put the key in as well. Let’s see the IPO’s PF authentication, and we can give the authentication if it is a plain text and authentication key. And suppose if I’m using authentication, then I have this option for message and digest. Actually, Cisco has given you a rather perplexing option because the obvious natural thing to do is to check the IPOSP of authentication and then whatever authentication is present. But in the case of message digest, you should go and check IPOSP, and then you have this option of message digest if you want to put your key. So I’ll put key as the CNP, but let’s see MD Five, and then this is a long command that we need to put here. Now, if you go to the show IP OSP of neighbor, we can see that neighbour is down due to a mismatch because the key is not configured on the other side. So we can go to routerOSPF one, area zero, authentication message digest, and interfacezero slash zero IPOs PF message digest key here as well. We’re finally getting it. So now you can see that the neighbour is coming back up. This is the way that we can go and do the authentication inside Area 0. Now, what I want to do here is first of all do the OSP for the rest of the configuration, and then we’ll create the virtual link. So let me do that.

One is okay. Let me check “Show IP Route” and what network we have configured so far in R 2. So we have Router OSPF One. We should have one more network, which is ten dots. Let’s take a look at the network; it’s 10 1 20. So ten are 120-0255. And that is inside Area 1. Correct. So this network is in Area 1. We have switch number 10 one.So let’s do the configuration for switch number 10 and see what network we have. We have a network of 10, 1, and 30 computers. That is in area number two. Then we have a network, say 10 110 110-1101.For example, suppose I put this in area one, and then I have ten, one, and twenty. That is inside area number one. All right, so we are very much done with this OSPF configuration. Finally, we have switch number 10-2, which is connected to the ten-1-30 network. So I’ll go here as well and enable OSPF. And then we have the network. So, for example, first of all, I’ll advertise the loop back. And this is inside area two. Finally, there’s Network 101.3. That is again inside area number two. Now here you’ll see that after running all these commands, we go and check “Show Iposp neighbor.” So he has two neighbours who are 10 2 and 10 5. If you proceed to switch number five, you will find show IPOs PF Neighbor. So he should also have two neighbors. But if you go and check the show IP route for OSPR, you’ll find that he’s not getting 10210-2 because it is never tunnelled or passed through area 1. So in this case, we should go and create the virtual link. Okay, so let’s create the virtual link. I’ll go and create the virtual link here inside area number one. So first of all, 10 five, and then 10 two. So already we are here in router OSPF1, area 1, and then the virtual link. What is the ID?

So we know that whenever ID is this, we have an option for message digest key as well, which I’ll explain later. But that’s it. area virtual link and then the peer device router ID. Now I’ll go to 10 one.I’ll come here and configure OSPF One. This is and remove this, and that’s all. So, if you go ahead and check the OSPF, you’ll notice that you’ve started letting the route. Now, in this case, because you don’t have a key configured, so inside area 0, we have the key configured, and you should go here and give the key so it works properly. Go ahead and give the key while saying CCNP. And now you’ll notice that they’re getting the route. So, if I check “show IP USPF neighbour now show IP route OSPF,” I should get 102-10-2102. That will be the final valid verification for this. So after running this command, I can’t see that anything is happening. And let me go ahead and check here as well. You can see that this configuration is 100% correct. You’re establishing a virtual link with this and in Router One, along with the configuration key; everything is correct, but they’re still not forming this. So what we can do is go to the router OSPF one more time. I’m in one location. Say, for example, that the authentication is message digest. This belongs to Area 1. And here we have area one as well. Let’s see the final configuration now that we have an invalid key for ten slashes that we can verify. So what is actually happening here is that if you go and check the configuration, you’ll find that once you’re putting the key here over the virtual link,

This is now assigned to inside area one. These are the interfaces where you have to put the authentication key. So, for example, MD 5 But when we are creating the virtual link, actually, in that case, that is going to propagate only in area zero only.So it’s not required to put the key there. But, just for safety’s sake, I’ll put the key over 100 and e one slash two as well. So 100 and OSPF message key one MD five CCNP are correct. And then, finally, I can go here and enter. So this is how much configuration we have done. And now if you go and check “Show IP OSPF neighbor,” First of all, we should have a neighbor. And if I go to Rwanda and check my IP route, So here you can see that it is getting the route because it is directly connected with area zero. And we don’t need to put actual authentication over the interface area that I’ve created. But, for the sake of security, we want to put the authentication key everywhere. So you can go and put the authentication keys in all these places.

22. OSPF Summary Area Types & Default Route 01

Next in this important section, we have the OSPF summary of different types of areas and the default route concept. So let’s start and understand the summary. Now clearly, you can see in the diagram that you have area zero separated by areas one and two. And, for example, if you get routes up to seven, you can see on the other side that it is 89 up to 15. Now we are sending all these routes to the core router. Here you can see all the individual routes, and hence the database or the topology table inside area zero will increase. Rather than what we can do, we can summarise area two as area one is 21; 21 is correct. So in that case, we are sending only one update, and our routing table will be efficiently utilized. By doing so, we can reduce the load on the router’s CPU. So this is one of the interesting use cases we have with inter-area OSPF summarization.

Now what’s the command? The command is very easy and straightforward. We can go to the router, and over the router, you can go to the area, and then you have to use the keyword “range,” and then you can use the address and the subnet mask, and then this will be done. Now there is one important point to mention: if you have some of the routes in between that are not part of subnets, So for example, if I don’t have one dot five, one dot six is still ten in this summarization, which is 10 00:21. So in that case, what we can do is use the concept of static route null zero and point out this summary route toward null zero. So that means that anything that is not matching will be garbage; it will be in the “bit bucket.” Correct. Now you can see that we are now running the modern or advanced version of the operating system after twelve. Even this command is not required. It was required for the earlier version of iOS. Now the second point related to summarization we have is that if the summarization is coming from the external system, it’s not related to inter-area routing but it is coming from outside.

Now, at this point in time, we should go to the ASPR. Suppose router B is an ASP who is connected to a non-OSPF domain or non-OSPF routing protocol. So in that case, you can do the summarization, but the syntax will be a little bit different. So in this case, instead of doing area, we do the command’s summary address and then the network and the subnetmass, meaning whatever network we want to summarize. Correct? So this concept is very similar to when we are doing aggregation, and we have two types of borders: AVR and Asvr. And like that, we can easily do the sunrise. Now here you can see that we have one use case in the case of ASB, which is that you don’t want to advertise certain prefixes. So in that case, you can go specifically to that particular network and use the keyword “not advertise.” If you do not advertise, obviously these networks will not be advertised inside the US PF.Okay, so this is the concept related to summarization. The next important concept we have is the OSPF area type. Now I have one summary chart as well, where we can go and summarise the OSPF area type after a few slides. So here you can see that you have areas typed “backbone, “non-backbone stub area,” “totally a stubby area,” and “not so stubby area,” which is NSSA in short. So, let us learn and talk about the area type. Now, starting with the basic area, that is, the normal or standard area, We know there are LSA types one and two in that area. So here you can see that we have all the LSS inside the standard area, the type 1, type 2, type 3, and type 4 generated by ABR. Then we have type 5 as well, which is generated by the ASPR. As a result, it can comprehend all of the LSA.

That’s the standard area. Now the second thing here is that when you’re making a stub, at the moment you will mark the area as a stub. The stub will not accept types 3 and type five.However, keep in mind that they will automatically inject the default route. You can think like this while doing so. While doing so, we are cutting off the SPF calculation. And who is doing the SPF calculation? My CPU, my process So that means that we are cutting off the intensive CPU cycles, and hence we are providing a good type of optimization in terms of CPU and memory correct.Now, what’s the command? Again, the CLI command is very easy and straightforward. You can go to the network. So here you can see the router process. First, go to the router process, and then you can go to area one stub.When you complete the stub, it will begin to stop type 4 and type 5. Despite this, it will receive a router network and a Bergen LSA. That is type one, type two, and type three. And another thing is that it is generating the default route. Now the third concept we have is the totally stubby area. A completely stubby area will only accept types 1 and 2. It will not accept type three, type four, or type five LSS, although it will go and generate a default route for type three, type four, and type five LSS. Again, the application is that we save bandwidth, CPU cycles, core process cycles, and so on. Now the command here is interesting because we have used it in a stub area. We have used one stub. For a totally stub area, you have to add one more keyword.

That is no summary. So the command is “area one stub,” no summary. It will terminate LSAs 3, 4, and 5, and generate the default route. Okay. Now the fourth one is not so stubby area.Why do we require a more stubby area? We can see that you may have a chance that area zero is connected to an external network, or you may have a chance that area one is connected to an external network. Correct. So in that case, we’ll see that when you have area one connected to an external network and you want to filter some sort of LSA, you are going to use the “not so stubby area,” which means it’s a stubby area but it’s not a fully stubby area. What will it do? Type 1 and type 2 LSS will be shared, just like standard stub area NSSA area routers. Okay, they are not blocking types one and two. The NSSA area will also accept type 3 LSS. So they are going to accept types 1, 2, and 3. But NSSA will not accept types 4 and type five.Okay, now we are going to introduce one new LSA, namely LSA Type Seven, that we haven’t discussed so far. However, the not-so-stubby area is linked to type 7. And what’s the use of LSA type seven? Now we’ll see. So if an Asbr exists within the NSSA area, this Asbr will generate type seven LSA. Again, NSSA areas are almost identical to Stab areas. If area one was configured as NSSA, it would not accept any external route originating from Router G ASB or outside area one. As you can see, they are not accepting any type 4 or type 5 LSA, only our type 7 LSA. So here you can see that it will not accept this as rude. Any external network will be rejected. external non-OSPF domain network. Correct. Great. However, area one also has an ASP within the area of Router A. Those external routes will be flooded into Area One as Type 7. As you can see, you have inside area one, router one, and whoever gets the external routes will flood inside area one. Now, these external routes will not be forwarded to other areas as type 7 LSA.

Instead, they will convert it to type 5. That is the key that I will summarise for the five LSA by area one ABR, Router C. So what is happening here when you are creating a not-so-stubby area? In that case, you are getting type 7 LSS and Router C. What will you do? He will convert type seven LSA to type five LSA, and then it will flood into the other area, or the other area will calculate as per the type five LSA update. The configuration is very simple. You must enter one keyword, go through the route process, and then choose one NSSA. Okay? All right. And the final concept we have is a totally non-swift area. So let me stop here and discuss the remaining concepts in the next recording. But here you can see the summary. And in this summary, let me try to highlight the backbone of LSA 1234 and 5. They don’t get LS 7, non-backbonelike area 1, area 2, and so on. They are also getting all the LSA stub areas, LSA 1, 2, and 3. Only LSA ones and two are available. Remember, they are going to generate the default route, the not-so-stubborn area. Types 1, 2, 3, and 7 are the most common. This type seven will be converted to type five, and then it will reach area zero. That’s the overall summary we have for this recording. So let’s just stop here, and the next section will continue from here.

23. OSPF Summary Area Types & Default Route 02

Let us continue where we left off. The following concept, however, is far from stubby. That is TNSSA. So what is the main difference between a stub and a totally stub area? The same difference you’ll find between a not-so-stub area and a totally non-system area A totally not-so-stubby area will allow LSA types one and two, and he’s going to filter types three, four, and five. Here, you can see the configuration is very straightforward. You can go to the OSPF area, and then you can give that area one NSSA. The key word is “summary.” And here we have the summary just for your reference. Now the next topic we have is OSPF and its relationship with default routes. We know that when we are generating a stupid area at that time, the OSP process is generating the default route.

But in the case of a VR, and as we are inside a standard area, we don’t have a default route. Now, suppose you are sending LSA type three fromrouter C and you are expecting that you aregetting the LSA type five from router one. So you’re getting LSA-5 from router 1, and it will go to router C and then other areas. Likewise, LSA type 3 will go to B and A, and actually B and then A and then the external network. At that time, suppose for the external network you want to create the gateway as router A, so we can go and create the default route. As you can see, forcerouter A also generates a default route with itself as the next hop for the external network and injects it into this inside area one. What is the command? The router process is represented by command. Go to the router process and let the default data come from there. So this will be the default route. But let’s say you want to push it. So, even if a default route does not exist in the router’s routing table, the router will be forced to advertise one using the always command. So in that case, if I want to force the default route.

24. Eigrp Overview & terminologies 001

In this section, it is assumed that we know EIGRP and the difference between EIGRP and OSPF. So let’s talk about EIGRP. What type of protocol is this? Basically, EIGRP is Cisco proprietary; it’s an advanced type of routing protocol or distance routing protocol. It is using a dual algorithm; its protocol number is 88; it is forming the neighbour table, the topology table, and then the routing table. It’s basically based on bandwidth plus delay, but there are three other factors as well inside EIG. So let’s drill down inside EIGRP. Now here you can see we have some points. I’ll go through these points, and then we’ll discuss a very interesting point inside EIGRP that’s a little confusing as well. We have a dual algorithm inside EIGRP that is a diffuse and update algorithm that will ensure that we have a luxury routing environment. We have to define the autonomous system for EIGRP. Inside EIGRP, the multicast address is the link local multicast address of 2240 00:10. Just to form the neighbour relationship or to check on the neighbors, we are sending these multi-card packets and hello packets.

It ensures delivery by using a reliable transport protocol and does not send periodic updates. It is also supporting VLSM (variable-length subnet masks) because this is the classless protocol. Other points that it’s ad is 90, external ad is 170, and the metric heavily relies on bandwidth and delay, but if you look at the metric calculation, you’ll notice that we have three more factors: reliability, load, and MTU. MTU is not mentioned in some books as part of bandwidth or metric, but most of the time, we will calculate the metric with respect to bandwidth and delay. Because this is a distance vector protocol, the maximum hop count is 224; the default hop count is 100. Distance vector protocol generally depends on hop counts as well. They will create three tables: a neighbour table, a topology table, and the routing table in EIGRP will be formed from the topology table. Again, we have the neighbours and, by default, the neighbor. They are sending the hello packets every 5 seconds, and in the case of a slow link, the hello packet timer is 60 seconds. Likewise, we have the dead timer as well, or the whole down timer as well, not dead but the whole down timer. That is three times of hello, which is 15 seconds, and again, 16 to 3, which is one eight-zero second.

We have to configure By default, it will be like this. But if you want to change the name of the relationship per interface, you have to go to the interface, and then you have to run this command: IP halo interval EIGRP. Then there are the autonomous systems, which in this case number ten and seven, respectively. I must go there and enter IPhold intervals EIGRP 10 and 21. So seven times three equals 21. That’s the hello interval and the dead interval that we can form. Now, in the last section, I will run that showIP EGRP command, and I’ll show you this output. This is something that, once you run the neighbour command, will be in the neighbour table. Remember, we have three tables: the neighbour table, the topology table, and the routing table. So in the lab, we will check all three. If you want to check the locks, you can use the law command in a later section, along with log neighbour changes and log neighbour warning. So these are useful commands that we can run and check. Now, I told you that we have an interesting concept inside EIGRP that is also a little bit confusing as well.So let’s try to understand the feasible distance, advertised distance, feasible successor, and feasible conditions like that. OK? So here you can see—let me read this out—and then I’ll show you in the diagram that all such routes are added to an EIGRP router topology. The feasible distance will be the route with the shortest network to network distance. The feasible distance for each network will be installed into the routing table. That is nothing but the successor. So we have a successor, the primary route; we have a feasible successor, which is the backup. Again, the feasible distance is derived from the advertised distance. Now, you can see that you can get terms like feasible distance, successor, please-well condition, advertisement, and so on. So let us try to figure out exactly how it works. 

25. Eigrp Overview & terminologies 02

Let us pick up where we left off and try to understand the terms used within EIGRP. Now here you can see that in the diagram I have A, and to reach the destination network, it is going by BC and D. Now, for BCD to reach the destination, the feasible distance is six plus two eight, nine plus 1423, and four plus five nine. So these are the feasible successors, respectively, to B, C, and D. But what about A? Now if you go to A, it has to add his distance as well. So, if you go ahead and add, you’ll find that eight plus eight that I believe I have in the next slide. So let me go to the next slide. So here you can see that eight plus eight will become 16, then 23 plus 427, and then eleven. So obviously, eleven is the lowest one. So that’s why he’ll get his successor in this direction, right? So now I have my successor. But we know in advance if you have multiple paths and if they will meet certain conditions, then you have the backup path as well. That is nothing but a feasible successor. So let’s first understand the algorithm by which EIGRP is finding a feasible successor. So, as you can see, it is explicitly stated that you have a feasible successor if it meets the condition. Feasible condition? What is that condition? A route only becomes a successor if its advertised distance is less than the current feasible distance. Now, in our case, we’ll go and try to understand this statement. So in our case, as you can see, they say the advertised distance will be less than the current feasible distance. That is the statement that will serve as the backup path. Now here, if you go and check so already I have a successor.

So it is marked as a successor. It will be installed in the routing table. Now, while searching for the feasible successor on the backup path, let’s see what the feasible distance is. So your feasible distance is eight. Here, your feasible distance is 23. We are adding 14 plus nine. And what is your distance? Advertised distance. So you’ll find that your advertisements’ total path is eleven, correct? So now you can see that it is less than eleven. So it is less than eleven—that is the correct condition. In other words, depending on which path you take, the feasible distance should be greater than the advertised distance of your neighbor. So because eight is greater than sorry, eleven is greater than eight, or eight is less than eleven. So that’s why this is a feasible successor. That is not true in this case. Because this is 23, which is bigger than eleven. Okay? So that’s the algorithm that you can verify. I will upload this slide as well. Finally, in these slides, if there is a failure and you do not have a backup pass, the EIGRP algorithm will be rerun and it will move to active, which means actively. It will attempt to obtain the viable successor or the backup path. Right. I’m right. So let’s just stop there.

26. Eigrp Packet types & Metric

Now that we have EIGRP packet types and EIGRP metric values in EIGRP, we have five different types of packets: hello packet, update, query, reply, and acknowledgement. Obviously, when devices attempted to form a neighbour relationship at that time, they were sending and receiving hello packets, and because the mode is multicast, they were using the 22:40:00:10 multicast protocol to do so. Apart from that, we have updated packages, which means if I discover a new neighbour, I want to sync my topology and routing table. So for that reason, I can send the update package. Now in this case, with new neighbors, they are using unicast, but suppose if you have any change in the route metric at that time, they will use multicast as a transport.

We have a very important packet type that is query. Because suppose your successor and your feasible successor both failed and you don’t know how to reach the network or you don’t have the network update, at that time you are sending the query package that asks, “Do you know this network update?” and you will wait for the reply. So we have the query, which means the router places itself in the active state, so I’m in the activist state, I’m sending the query packet, and I’m waiting for the response. Now the reply package is sent to give the response for the query packet, and this reply packet is sent as a Unicorn to the querying router. Now we know that EIGRP uses a reliable transport protocol, so that’s the reason we don’t have acknowledgement for the hello packet or acknowledgement itself, but for all the other packets like update, query, and reply, we do have acknowledgement. So here you can see that the following packet types employ RTP to ensure reliable delivery, so that’s why we have acknowledgement for an update, query, and reply package. In EIGRP, we now have two states: active, which means actively looking for neighbors, and passive, which is the stable estate. So once the routing has been converged, your topology table and then your routing table are stable at that time.

That state is passive. If you are still looking for a network or are still having problems with the network, move to the activist state. We now know that in my activist state, when I don’t have a successor or a feeble successor, I sent my query packet and am awaiting a response. Suppose if it takes three minutes to take the response back, that state is termed “stuck in active.” So you have sent your request and you haven’t gotten a response, and for three minutes you are stuck in “inactive.” You got stuck. There are now some solutions to this stuck inactive phase. Either you can do proper summarization, network summarization, or you can use Eigrv features such as the tub. That includes your hub and spoke. Thank you. You are the main router hub, and then you have the spook and those spokes. If you convert those spokes to stubs, the query will not propagate and the bandwidth will not be overutilized. Okay? So we’ll see that concept of a job later on. Then we have the verification command in the last section. We will verify, we can run show IP, and we have EIG epitopology.

Here you can see the state quotes: P for passive, A for active. If it is converged, then B is passive; you have one successor or two successors, etc. So we can get that information. Here is one important point that you can see: you have a feasible distance of 229-7856.Now, how EIGRP is calculating his feasible distance is what we are going to discuss, and that’s a very interesting calculation we have for the EIGRP metric value. EIGRP uses five parameters to calculate the metric value: bandwidth, load, reliability, delay, and MTU. Now here you will see that in some places it is mentioned that the MTU will not come into the picture. Anyway, we have these five k-values for these five parameters, which can be thought of as variables or components of the metric. Now, with these five components for the metric value, we have one very complex formula. So let me show you this formula. Here you can see the formula. That metric will be calculated as k divided by the minimum bandwidth, then plus k two into the minimum bandwidth, 256 minus load plus k three into delay into k five divided by k four plus k five divided by k four plus liability into 256, where your bandwidth is ten to power seven by dividing by the minimum bandwidth. Now this is a really complex formula. So to make this simple, what is happening generally most of the time is that the system using kone, k four, and k five, as you have kone and k three, is limited in bandwidth and delayed.

And that’s the reason you will find that the calculation for the metric will be dependent mostly upon bandwidth and delay. Again, you can see that ten to the power of seven divided by bandwidth, plus delay, will be in microseconds, and this bandwidth will be in kilowatts. so kilobytes, and the delay will be in microseconds. Again, the bandwidth will have a very large impact on the metric calculation. So that’s why you can think of it with this formula as being indirectly proportional, not directly proportional. So sometimes, if you check the calculation, it’s inversely proportional to bandwidth, right? Because you can see ten times the power of seven divided by the minimum bandwidth. Obviously, if you have the eleven, you can add that, but the major role is played by the bandwidth. All right, so this is the formula to calculate the metric. Now, how do you want to apply this metric if you want to change certain parameters? For example, we have CLI amounts in metric weights ranging from zero to five. And suppose you want to add any of these things. As an example, I’m converting k three to one. So, in this case, K is one. Then again, this formula will get changed, correct? So in my case, k two, k three, and k four As you can see, K 2, K 3, and K 4 will all be one. Then again, this calculation will get changed.

Again, it’s highly unlikely that we are going to change the metric value; whatever the default is, we are using it. But in certain cases, if you want to do some sort of traffic engineering, some sort of load balancing, or some sort of change in the metric calculation, then you can go to the interface and either increase or decrease the bandwidth. That was something we were used to doing for traffic engineering. Either we are changing the bandwidth or we are changing the delay factor. So either if I change the bandwidth or the delay factor, I’m going to change the metric calculation as well. Okay? We have one command again: IP bandwidth, percent EIGRP autonomous system. And, by default, EIGRP consumes 50% of the link bandwidth. And suppose you want to make this 30%, you can do so as follows. Your link’s bandwidth is 64. So you’re using 30% of 64. With this command, we have options that we can use 100% of the time. And again, if you want to change the delay, you can go and use the delay as well. So let’s just stop here. And in the lab section, we’ll try to understand more of what we have covered so far.

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