27. Eigpr Basics Lab
Let us do the EIGRP configuration, and after that configuration, we’ll go and verify first of all the basics, like how EIGRP has their neighbour table, their topology table, and their routing table, plus we’ll see the various types of packages and kit types that they have. Then we’ll go and check the other things that we studied in the previous section. So let’s get started, and what I’m going to do, as you can see in the diagram, is connect switch r1 and switch 105, so you can see the interfaces between those two switches. I’m going to assign the IP address to all these related interfaces, plus I’m going to give one loopback address as well, just for verification or testing purposes. So let me quickly go and assign IP addresses to all these interfaces. I’ve assigned IP addresses to all of the interfaces, and let me quickly demonstrate that we can go and verify once I show the IP interface brief and I’d like to include the manual. We’ll go ahead and run this on all these devices. 101-102-1035 and R1 and should press enter to send a script, so we can see that I have this IP address over R1, then switch number ten five. I have these IP addresses, although I haven’t ping-verified whether they are reachable or not, but I have assigned the IP addresses over the interfaces and created over-the-loop back interfaces as well as per-hour topologies. Okay, so the next task I have is to run EIGRP.
So let’s go and enable the EIGRP router EIGRP.We know that we have to give the autonomous system credit for that. So let me show you the global configuration mode router EIGRP from here. and then we can assign the autonomous system. For example, I’m using ten. I’m going to use “no auto summary,” which means I don’t want to do the automatic summary. As a result, this is not an auto-summary command. Then I want to advertise the network. Now we know what type of IP we have. If you want to check the network connected network, you can use Show IP route or ShowIP route to get the list of connected networks. But because I have this network here, I can go and use it, and then we have this option where we can use the wild card bit. Then I can go and use the other network. Then I have another network as well, which is this one. And I can go and use the wildcard bit here as well. Then the third and fourth ones. So this is my third network. And then finally the fourth one, the loopback address after slashing 32 in the CIDR, So I’m going to use this as a WiFi bit. We can quickly check the Ergf configuration. So here, you can see that we have these main networks. Now I should go and enable this on the other devices as well. As a result, we changed the configuration to 10.1. Allow me to do 10 three. So, for 10 three, let’s go to 10 three routers EIGRP, and we should have the same auto-number system, but no auto-summary.
Then there’s the network, which we know is this. When I enable or run this command, you’ll notice that they’ll start forming the neighbour table, the topology table, and the routing table. So the dual algorithm will run here, and you can see that it is running the dual algorithm, and then we have the routing table as well. Okay, so at this point, I can go ahead and check Show IP EIGRP first of all the neighbour table. So you can see that this guy is the neighbor. We don’t need to worry about this request timeout, the queue count, the sequence number, the round trip timer, and so on because the uptime is this millisecond rest of the things. If you have any issues at that time, you’ll see that the queue count is increasing, the RTO value is increasing, the trip timer is increasing, et cetera. Okay, so the first table will be the neighbour table, and then you can go and check the other stuff as well, like I can go and check the Show IP Tigret topology table. That’s the database you have. Now you can see that you have the successor, feasible distance successors, and also the metric value. So here you can see your FT values. This calculation will be discussed in a future slide show, but we can talk about it now because I need to open the mathematical calculation and the calculator. So for that, we’ll go and check what the bandwidth is and how this calculation is coming into the picture. That’s 409600; that’s the Ft. Again, you can see that PS stands for passive, and then you have all the quotes. So let me quickly open the calculator, and let’s do the calculation here. So we know that the metric value is roughly the symmetric value, which is Q 56 divided by bandwidth in Kbps, plus some delay. This is a rough calculation, so let’s try to understand first of all the bandwidth for the interface. Everywhere we are using Mbps, so my bandwidth is 100 Mbps.
Now that we have 100 Mbps, let’s calculate it in KVPs. So let’s try to do this now: ten to the power 74567 divided by 100 Mbps means 100 into 1000 means we have to convert into kbps. So the number of zeros will be zero, which equals 100, followed by 30, which equals Kbps. So the final value will be 100 plus the delay. So I should go and check the delay over the interface. As an example, display interface E 0 slash 0. Now if you go here and you can see the delay, this is in microseconds; this is ten to the power minus six. That’s the microsecond we have, and that’s okay. So what will be the value of this? 1000 divided by ten to the sixth power? Correct. Okay. And that’s the correct format, actually. So let’s see. Let me open the calculator one more time. So that means we should go and add 1000 here, and then if we do 256-28-1600, I can see the bandwidth in kilobits that is showing ten to the power of four only. And let’s go check that our metric value there is 281600. That’s correct. So yes, let me open the calculator, and here you can see you have the exact 2816-002-8160. So this is the way that we can do the calculation for the metric system. Okay, so what I’m going to do here now is just stop here, and in this lab we will study some theory, and again, I’m going to continuously build this lab in the upcoming sections as well.
28. Eigrp Passive-Interface & Auto-Summarization
Let us understand some more terminology and theory for EIGRP. And likewise, we are going to continue our lab as well. So the next topic we have is related to passive interfaces, or summarization and authentication features. Let’s see how it goes in this slide step by step. First of all, when you’re doing the baseline configuration that we have already done, go and enable the EIGRP process with autonomous systems, and then we have the option to advertise the network. Now we can go and add the wild card bit as well, so we can get the specific network advertisement. Once we get up to this point in time, obviously, we know that the hello packets will start exchanging, and then they will form the neighbour relationship. First of all, we have the neighbor relationship, a neighbor table, then the topology table, and finally the routing table. All these things are going to be seen in the upcoming lab as well. Then suppose you don’t want to form the EIGRPneighbor relationship as we did previously in OSP. So then I can go to that particular interface, and I can make that interface a passive interface. The standard format is to deny all interfaces (such as the passive interface default) and then add the interfaces that want to do the EIGRP hello exchange or EIGRP packet exchange selectively. So for that, we have the passive interface default, and then we can go and give low the passive interface and then the interface name.
Now again, we have learned this in OSPF. That is how we are going to do the summarization. In OSPF, we can do a summary or a summary by area. So we have used that command. I have shown you how that command works or how we can use that command, and then we can do the summarization for ASPR as well. So we can summaries a BR and sabra in EIGR; this summarization is relatively simple. So first of all, in the previous section, in the last section, we used the auto summarization because if you do not do the auto summarization, in that case, it can be converted to their class boundary. So, if you have network ten (10 00:16) and do not use the auto summarization feature, such as noauto summarization, it will believe that his network is 100 zero because ten belongs to class A, whose subnet mask is 2550 zero. As a result, we must use this keyword, such as “no auto summary,” and then proceed to manual summarization. Now, the same thing that we have discussed in the case of OSPF, you have to go to the interface and then summarise EIGRP, the autonomous system, and what you want to summarize, so you can do the summarization. I’m going to COVID this in the lab section, where we’ll create various types of networks, summarise them, and then send them to the devices. Now, when we do the manual summarization, at that time the ad value is five. We know that the internal ad value is 90 and the EIGRP ad value is 90, but for the sake of synthesis, we’ll use five. As with auto summarization, the router performing manual summarization will add the summary route to its routing table with the next hop of zero null interfaces. So we know you’re not summarising enough or summarising too much.
See, that’s a combination. Do the no auto summary; you’re not doing the summary automatically, and then you are doing the manual summarization, and that’s the reason we have this added stress of five. Obviously, that is more than the internal distance. Okay? So, do not combine autosummarization with this practise of no autosummarization followed by manual summarization. Then finally, in this section, we have the authentication. First of all, we have to create the authentication key. So here you can see that the keychain defines the key 12345, et cetera. Then the key string defines the password, and we have to go over the interface and apply it like IP authentication keychain, autonomous system, and then key if the authentication or password matches for both peer interfaces, then only they will start exchanging EIGRPs. So, these are the topics I’ll be covering in COVID. Let me open the lapse section and show you whatever we have discussed here and what we have left over in the previous section, as well as what we have done that we have enabledergr 10 one and 10. So, if I go here, I can show you show ipeigrp neighbor, show ipeigrp topology, and show ipeigrp better, I do show IP route EIGRP; that’s the routing table. So whoever is your feasible successor, you will see them in the routing table as well. So you can see what network I’m learning here, and why it’s included in the list of all the networks that are actually connected. So you can see all our connected routes, and then finally, I’m learning one of the loopbacks. So that’s why it’s coming inside this routing table. First and foremost, we should double-check everything. Then, if you want to check the packets, we have the show IP EIGRP command, which allows us to see the traffic and see what type of packets we have: hello, update, query, reply, act stuck inactive, and all of the other packets we have. Okay. Then we can go ahead and change the metric values that we discussed in the previous section.
I can go to EIGRP, and then you have command metric weights, and then you can see that, for example, type of service is k one, then k two, for example, then k three, so like that we can go and put all these values. I will not put this value, and they’re showing you that you can go and check these values. Let me go here, and let me show you IP route E as E RP. So you can see that you have your ad value and your metric value here. If you go to the interface, it’s between interfaceE two and zero two. So here we are, about to switch from 10 to 3, and I have the option of changing the bandwidth. So if I change the bandwidth to $5,000 and check run interface E zero slash two, show interface E zero slash two, you can see that the span width is 5000 and it is 5000 here. Now, go ahead and check the matic value because we know that it will change. As a result, it has evolved into this. It was 123-4566 at first because I believe it was 1000, or one and four times zero bandwidth. Now, if I go up and show you the bandwidth before changing by one, that is increased because the increase in bandwidth and metric is inversely proportional. So if this number is increasing, that means the bandwidth is decreasing. What I’m telling you is that if you go to interface E, zero two, and if you give the bandwidth, say, for example, one more zero, So if this will increase, this will decrease, correct?
Do show IP and EIGRP. Do show IP and EIGRP. So now you can see that this is decreasing. So if you increase the bandwidth, your metric will decrease, and that will become more and more preferable. All right, so these things are related to the previous section or whatever things.We have a study now; let’s cover that. So first of all, we have a study about the passive interface. If you come here and allow me to do one thing, I’ll enable EIGRP on these devices as well as 10 1 and 10 5. So let me quickly go to 10-5 and enable E as ERP. Before I do that, let me see what’s inside 10.1 and what interfaces we have. So we have one, two, or three interfaces, and that’s correct. And then we’ll go here to 10 5 and add we’ll add the interface basis. So ten, one, twenty equals one, two, and three. All right, so let’s do this. The router is EIGRP-10, no auto-summary network ten, then we have two and three correct, and then we have one loop back as well. So two, and then we have three, and then we have network-related numbers: one zero five, one zero five, zero zero two five five. Okay, so the fact that the network we have now is not coming up indicates that something is wrong with the interface, that it is down, or that we need to check something. So, if I go to do show run interface e100, I can see that the interface is correctly defined. Then I’ll go check e1:e2, and if I check showrunsection, it should have a routing for that as well.
So far, I’ve seen ten 12012 dots; some appear to be related to connectivity, while others may be intervals that we need to figure out. So you can see the problem here. My interface should have a correct IP address. So the IP address is 10:12:105, and you can see that the error was two and one. But again, you should give the correct IPS. and now it is up and running. I can go look at show IP EIGRPtopology or show IP route EIGRP if that’s what I’m looking for. So you can see that it is getting the loop back 10 three times and the loop back 10 one times. That’s why I’ve given the loopback addresses. So that means I have reachability now if I go to 10, because he has two neighbours at this point in time. So, as the IP neighbor, I want to create a passive interface with one of my neighbors. So for that, I can go to router EGRP and say passive interface default. That means everything is passive. Then there will be no passive interface, i.e. For example, if I take one of the last two, I can enter no passive interface for E 0. This is also the use of a passive interface. So, now that we have the summarization option, what should we do? So for that, I can ask you to let me open this diagram. I can go to 10-3, and I can create some loopback addresses here. So, for example, seven, or maybe 10 and 3, or anything. So let me go and create some of the loopbacks. I’ll go to 10, 3, and make a few loopbacks. Say, for example, interface loopback 10 one, IP address. Say, for example, two two one, then interface 10 has two IP addresses: two two three. Like that, I can go and create some of the loopbacks I want to do the summarization for. Then I can go to router EIGRP 10. If you want to check your loopback, I can make an advertisement for “2 2 7 do show IPinterface brief.” So 341-0110, two, etc. But the network is 1234. Now if I can go and check these routes here (show IP routes for EIGRP), I am getting the loopback, so here you can see that we are getting four different food networks rather than one advertisement. So what can I do here that I can go to the interfaceso let me check what interface?Inside 10 three, we have a brief interface.
So let me show you this diagram here so we can go to 10-3, interface zero slash zero, and we can do the summarization. Okay? So interface 0 IP and then the summary address EIGRP 10, and then we can summarise and save the mask 2552-525-5248. All right, if I go here to see that the ad value is getting this single advertisement, that’s okay. And if I go to COVID, you can see that once you do the summarization, the EIGRP algorithm will rerun; it’s been resynchronized, and it has sent the summary. Now, if I go to 10:2, and here if I go and check, let’s see the final command. So what we have done is run Section EIGRP, and we have done this summary. Great. So we’ll go to 10-2, and in 10-2, also, I’ll go and verify that what exactly? What kind of advertisement exactly am I getting here? So we’ll look at our IP address to see where we are. I should go to 10-1 as per the diagram; we haven’t done any configuration for 10 two.So show IP route EIGRP and we are receiving this advertisement, and if I go to who is the originator sending the summary to the null, it is being advertised to all devices, correct you.
29. Eigrp Load-balancing stub Lab
Now we are going to discuss the theory of load balancing stub areas, and the authentication lab will do it in the upcoming section that we have already discussed. EIGRP is a protocol capable of sensing unequal-cost equal load balancing. So what does it mean? That is, if you have a feasible success, a feasible successor, or vice versa, one is your primary link, one is your primary path, and one is your backup. However, using variance, we can make both links active. So that means that we know the successor only gets installed in the routing table. But if you use the variance command, both the successors and backup successors, or the feasible successor backup paths, will get installed in the routing table and you will get them even though you have the unequal path.
So for example, you can see these two paths, but you will see that those things will be installed in the routing table. So you have the successor and you have the feasible successor; that’s your backup. But still, if you send four packets, two will go this way and two will go this way. Just as an example, on these devices, they are not doing packet-based load balancing but something called flow-based load balancing. So what’s the command variance? We’ll see how much variance we can use. We can use up to 128. In the lab section, we’ll see that the maximum path will be four by default. We’ll see that it has a maximum path load balancing capability of six. But in a higher version of the operating system, it may be more; by default, it will be four. Next, we have a step that we discussed earlier where if I lose my successor and a feasible successor, I will send the query packet and the query packet will be propagated until we get a response. Suppose I get the reply within three minutes; that’s okay. Otherwise, this process is known as being “stuck in active.” To mitigate or overcome this, I already know that the network is not looking for this specific hop or router. I can make that spoke router a stub. So that means that I am sending a query packet. But you will simply reply, “No, you don’t have what you are looking for from this direction, from this route, or from this gateway,” so that the query will be answered that this is the stub. Alright, what’s the command? We have the command; we should go to the EIGRP process. We can go and run this command, and then we have four options: receive only, which will not share the update with neighbors. We have connected, static, and summary options. “Connected” means to advertise connected routes. Static means the router will only advertise a static route. Summary indicates that the router will only advertise the summary route. Okay, so these are the hub’s options, and then we have some verification commands. We have seen this Show IP I GRP neighbor, and then we have seen the Show IP eIGP topology. We can check who is the successor, feasible successor, and add those values; we can already check Show IP GP Traffic; we have seen Show Interface, and you can check the interface, what is the delay, bandwidth, liability load, and so on. Show IP protocols we haven’t checked so far. So we’ll run this in the lab. Show IP Protocol will give you details about the protocol. It’s a very useful command. It provides the detail structure and detailing for that specific protocol.
We can check the routing table if you show the IP route; show the IP route EIGRP if you want to filter it. And then finally, we have some debug commands, such as “debug EIGRP neighbour packet route and summary.” Remember to wait until the maintenance window appears before running this debug command. So, from this point forward, we can go and log into the lab, continue our lab because we need to verify a few things one by one while load balancing the stub, and then do the authentication lab. All right, so we are inside the lab section. So far, we have run ERP 10, and let me quickly see that we have done over 10210. We haven’t run yet. So let’s go and do that. What kind of network do we have? Three and four are available. I can go here and EIG IP ten new auto summary networks: ten, one 40, and then the wild card; for other networks, we have 30, so I can go and do that. We have 30, and then we have network 1021. So here also, you can see that the EIGRP protocol is not coming up. Let me quickly go and check the interface. The IPS may or may not be signed. Correct. So we have four and three. It’s correct. Let me quickly check where it is connected. As a result, it is connected to zero and one slash two.
As for the diagram here, you can see that it should go to one, and it seems that this is a passive interface that we have done. So I can go here, and you can see how useful passive interface is. I can go and check the configuration first. I should not do a passive interface for E, GRPten. And, as far as I can tell, the protocol is moving in this direction. It’s okay; let’s quickly check ten and slash one. So I can go to 10-5 and look for the EIGRP protocol there. Do we execute the network command? So I can go ahead and check the section of EIGRP we have; is it correct? So we have 10, 110, 210, 1, 3, and that’s correct. Let me quickly check EtenonEnterface, and we have the incorrect IP address. So E ten 13105 followed by 255,255-2550. All right, so now we can see that it is working. Correct. When I check, it shows the IP route EIGRP. So here, you can see that you have the loop. So we have 105-10-1103 as a loopback. All of this we’ve finally gotten, so let’s go to router one and see if we have the EIGRP configuration, which we don’t, and some configuration related to summary that I don’t need, so I can go to zero zero and remove this command as your router. Ten new water summary networks, Ergip ten dots, one dot, zero dots Then we have one more loop back. That loop back is now, if I go to any of the switches, for example, 10 and 3. Also, I should get all the loops back.
30. Eigrp Authentication & Variance Lab
So let us continue and perform the lab related to authentication. And then we have the unequal cost load balancing, and then we’ll see what the command is for this job as well. So let’s start this. Here’s the topology, and you can see that I’m going to enable authentication between switches 1 and 10. E 0 is the common interface. So how are we going to do that? First of all, you need to create the key chain. For example, suppose the name is C and P in caps for emphasis. This is the name. Then key, I can give one, and then go give the key string, say CCNP, and then key, great. Then we have to go to the interface, e0 slash zero, and then we have the keyword called IP authentication. I should give the modes as EIGRP 10 and MD 5. So we have two commands: one is IP authentication, which I have left out for the time being. This neighbour relationship is clearly deteriorating. Then we have the keychain option keychain EIGRP, and the keychain name is CCNP. Okay, that’s it. So these are the commands we need to run in order to enable authentication.
I can now copy and paste to this side, and you can see that this neighbour is down. I can go and create the key chain first, then I can go to the interface, and then over the interface, we can also go and run this command. So let’s do this over the interface. I have this authentication command; we can go and enable this. Now we’ll see that the neighbour will converge, and now I have the neighbour relationship with the router, which is 10 1 10. Just now, it came back up 10 seconds ago. All right, so this is the way that we can do the authentication. Next we have the variance. So let’s try to understand the unequal cost of equal load balancing. Now here you can see that I can go and reach R1 via this path, and then I have the other path as well. So let’s try to check the loopback that we have here, which is nothing but one one.So, how many paths must we take to get to one from switch 10? If I go to switch 10 and check the IP route for 1111, I should give the network one. As you can see, I only have one way to get there via the last two. And if you go and check “show IP,” “EIG IP topology,” and then if we go and check “one inside the policy,” it is telling us that you have 2105 and 4102. So, as you can see, it can go two ways this way and five ways this way. Obviously, the FT and AD values in the matrix are different, but you now have two paths; is one of them a successor? So we know who will succeed him.
Successor is this because it has less square footage, as shown at 435200. And if you go and check this output in this manner, you will see that to reach one, I have only one successor, although we have two paths to get there. So, in this case, it will be direct: 10; the other will be y: 10; 2; 10; 5; and then R: 1. So what can we do now? I just wanted to add up the value for two different parts. So suppose if I want to decrement this, first of all let’s try to understand: can I do some sort of traffic engineering so that traffic will go this direction rather than directly? Let’s try: I have bandwidth defined and defined, which means I have to increase the bandwidth at two points: overswitch 10 one and then switch 10 two. Correct? because all the links have equal bandwidth. So, if we look at the bandwidth for interface zero, we can see that it has this. Now I should increase the bandwidth. So I’ll do 1234; I’ll go to interface 0 with zero bandwidth, say 51234. Let’s look at the show IP route for one and see how it goes. As you can see, it is still going at 10 and 5, indicating that it is still going directly. Now, what I’m going to do is go to 10/2 and change the bandwidth to one slash two.
So I am here; my bandwidth is 1234. If I go ahead and check, so what we’re doing here is forcing the bandwidth to change its metric value, and we can see in the show IP EIGARP Topology that it’s going via e one last two rather than e zero zero. And if you go and check topology for zero, one, Now, if you check the composite metric here and the composite metric here, we still don’t have much change in the composite metric. Obviously, the reason here is that you are changing the metric here and you are changing the metric value here. We should change this as well, that is, e zero and the bandwidth is, so we are simply forcing the bandwidth. If you go back and look, we can still see that it prefers this way. So IP routing means there is no change. While we have changed the metric to one, it is still going by the directly connected path. Okay, it’s still going in this direction. Although we try to change the calculation, it may still be less than what we are getting from two links. As an example, 10210 equals two. You can see the metric value here, 204800. And then if you go and check the metric value from here, So, if I check the showIP route, I should arrive at two one one. So switch number two is used to connect to router number one. Here you can see the metric. And if you go here, since the metrics are very much the same, how these guys are reaching is that they are coming to this point, and then it is getting advertised in these directions, right? All right.
So we can see that in this case, if you want to do traffic engineering, it’s very difficult, but one thing that we can do here is unequal cost equal load balancing, right? So if you have a successor and a feasible successor, then it will be very easy to do it. Now, in this case, I don’t have any feasible successors. So there’s IP ignology. So you can see here that I have only one successor. I don’t have any feasible successors. If I have a feasible successor, then it’s easy to do. But still, I can go and use the router EIGRPten, and then the command will say we have variables. I’ll give the worst case, which is 128. And then if you go and check “show IP route,” specifically I want to see one of the routes. But here I can see that 10510 5 now has two different equal-cost multipaths, although you can see the metric value is different. So if I go here to the topology, you can see that from switch 10 one, you reach 10 five. You obviously have one loop back. I have two paths, this path and this path, with different matrix values; one is 23001 and the other is 40 nine. And, according to how we’re doing the math, that’s 23040 nine. You have to simply divide it, and you’ll find it’s almost double.
So the difference is double. So what I’m telling you here is that when you’re using the EIGRP value, we’ve given you a variance of 128. That’s also the worst you can do with three. Then, if you look at the route, you’ll notice that they’re doing unequal-cost equal load balancing. And then if I go and check “show IP route” or maybe “show IP EIGRP topology” for this guy, I should do this. So now here you can see that you have this path that is going directly to a switch, then looping back, and then going via the other switch. And then here, you can see the metric values (this and this), where the difference is almost double. Okay? So I can see this now, and if I check IPA as the topology, So here in the topology, you can see that it is 10 five.As you can see, you have two successors. So at this point in time, it is showing two successors. Obviously, if you have a successor, then that will be installed in the routing table because we have made so many changes in the bandwidth as well. That could be one of the reasons values become so well balanced. So let me quickly go and revert the change. So I’ll go to 10 2 and I’ll change the bandwidth to E 1 2 and E 0 0. So let’s do this.
Bandwidth is 1234 e one two; the bandwidth is because, again, if we change the bandwidth, you’ll go and see the values getting changed. So for 10510-5, now you can see that you have only one successive, although we have used the command called variance. So if I go ahead and check the show IP route for 10510five, we can see that you have only one path. Okay, so this is the purpose of changing the metric value with the help of bandwidth. Although we know that we can cope with the delay as well, But I’m not showing here how we can change the bandwidth and then play around with the variance command. Finally, we have one use case related to Stub. So, suppose I have an issue and something will happen with my destination network somehow if I am unable to connect to my destination network, what will happen in this case? Suppose if 10 is the hub, then this guy here is the hub, and these are the spooks. So you can go to the Spook and simply enable the command called STUB. Assume this link goes down, and because it is the stub, the query will not be processed, and the stab will simply respond to the hub that you can’t go beyond me because I don’t have the network that you’re looking for. So, in this case, we can go directly here and check the stub command on the router EIGRP. So if we have EIGRP and Stub, I can see that you have a connected leak map but receive only a static summary. So we can get connected and summarize. Now you can see that it reran the algorithm. So now this becomes the stub, and the theoretical aspect of this we have already discussed. All right, so let’s stop here.
31. Border Gateway Protocol BGP
In Chapters 3 and 2, we have to study the border gateway protocol. Despite the fact that the slaves visible are very small, we should configure and test EVGP as well as perform some path selection using the base path selection criteria. But I’m going to start with zero. I’m going to start with the beginning of BGP. So what is BGP? What is IBGPP? Etc., etc., So, to begin, what is border gateway protocol? The first question that arises is whether there aren’t already protocols for routing protocols.There is one more reason why I require an additional protocol. Now, the answer to this is that this is the exterior gateway protocol, which means this will override or this will run on top of any of the underlying protocols, any of the underlying IGP protocols, and it will work as the application protocol. And that’s true if you see the port number that BGP is using; this is TCP port number 179. Generally, whether using TCP or UDP, applications use TCP port numbers. So BGP is a type of application protocol that is generally built to run over any of the other protocols and cross the boundaries of an autonomous system. Again, the autonomous system is one region, so cross one region, and then it can go to multiple regions. Or if you want to control multiple-reason routing for the network advertisement or the routing control you want across the multiple reasons, then that’s the protocol.
Or in other words, we are telling you that it’s a protocol for the internet, that it’s a highly robust protocol, that it has so many tuning options, that it has so many attributes, that we can tune it, and that’s the thing. So it says advanced vector protocol with high tunability that can travel across regions. It is a type of application protocol. Finally, it can interact with or hold a large number of routing databases or routing tables. Okay, as defined by the term “path,” we know that reachability varies from autonomous system to autonomous system; it is a distance vector protocol. It has the auto-numbering system number defined here; you can see from one to nine numbers are private and reserved. Nowadays, we have dotted notation as well for the BCP. Now, you can see why you want to use BGP. So, if you have multiple connections to an external autonomous system, that is, multiple exits or multiple ISPs connected to you, and those multiple connections are with the same carrier or provider but connect via routing policy, the existing routing equipment can handle the additional demands. It is highly tunable. So, if you want to do some sort of preference (path preference), load balancing, and so forth. So those things are achievable with the help of BGP tuning capabilities. The true benefit of BGP, however, lies in controlling how traffic enters the local autonomous system rather than how traffic exits it.
So the true benefit is that you have control over traffic when it comes to you or local authorities. Now, we can have two types of neighbors. We can have either IBGP or EVP exterior and interior BGP. IBGP means “within the autonomous system.” So in this diagram, routers B, C, and D are IBGP.PR. Or they can be IBGP or PR. And then different autonomous systems, like 100, 200, and 300, can be EBGP exterior VGPPS. Now we have options. That is the type of IVGPR relationship I want. Do we have full mesh, or what other tuning options do we have? We’ll go check later to make sure we have multiple options when discussing the internal neighbour relationship or interior neighbour relationship. Generally, when we are creating the IVG relationship, we should create it fully meshed. Otherwise, there are some other options for advertising the network that one IBGP is getting and advertising to other devices. Now, one device can be part of an autonomous system. And if you want to make multiple parts of it, it will throw an error. We have the ad value fixed for EBGP. The administrative distance for ad value is 20 miles, and the administrative distance for IBGP is 200 miles.
Okay? So that means the EBGP routes are preferred over the IBGP routes. So 20 versus 200 is better. That thing we know now is the BGP peer message; we have BGP peer messages; what type of messages do we have? So we have “open messages,” “keep alive,” “updates,” and “notification.” Now, “open” means that I want to form a relationship with my neighbor. And here you can see that an open message was sent between peers to initiate the session. The open message has several parameters, like version local, PGP, and router ID. Then you have to keep your life. Keep Alive is similar to sending the Keep Alive message to your neighbour to let them know whether or not you are alive. By default, BGP sends that keep-alive message every 62nd, 62nd divided by three, which equals 180. The second is the hold timer. So after three, keep a live message going. If you’re not getting responses, that means your BGP neighbour is dead. You will mark this as dead with the help of the notification message. So now this notification message is sent when there is a fatal error condition. If a notification message is sent, the BGPpeer session is toned down or reset anyway. If your peer is down, that means you will send the notification while the peer is down. Then we have the update message that is used to exchange the route between the peers. Now, here in the BGP state machine, which is the finite state machine, we have some other messages as well. So, what exactly is this? When a BGP peer session is forming at that time, let’s say I have two routers and I want to form a BGP neighbour relationship between them. So you will find that they will exchange some sort of message. These are ideal connections: they are active, open, confirm, and are recognised as correct.
So idle means that it is initiating the BGP state. Then connect, indicating that you are both waiting for the remote peer to become active and initiating the connection. Obviously, this connection is TCP; “open” and “sent opensent” mean you have sent the open message. Once you send the open message, BGP waits for a reply to keep the connection alive. So you’ve sent the message, you’ve received confirmation that the message is open and confirmed, and the finite state machine will establish the connection, correct? So it’s very easy. Ideal connections are active, open, send, open, confirm, and established. If your peer is still in activist mode, the potential issue is that you have a password mismatch. Maybe ACL is blocking port number 179, maybe you have an incorrect OS, maybe you have an incorrect neighbour statement, and so on. So if it is stuck in the active state, that means it is not good. You must then troubleshoot and make this work. Now, how are we going to configure it? We know that one router can be part of one BGP autonomous system. Go to the router’s BGP and then the autonomous system if it is an Evgp; if it is an Ebgpa, they have a TTL value of one. So they are always thinking that their next-hop peer is one hop away. So in that case, you don’t need to modify the TTL value; you don’t need to modify anything. Anything else indicates that router B of A is 100 and router C of A is 900. They have to give a simple command (router, BGP neighbor, and remote), is that it? Now if it is an IBGP peer, you can go and update the source. For example, generally, we are using loopback as a router ID.
So in the case of an IBCP neighbour relationship, you need this update source loopback command to be correct, and welcome to the EVCP multihop option as well. If you have an EVCP relationship and it is a multiple hop away, you can use the EBGP multi hops, for example 200, so this example simply shows that. Suppose you are using the loopback address instead of this physical address. If you are going to use the loopback address, which is again one hop away, then how will you form the relationship? So, for example, in that case, router C is using neighbour 1, and we can see who is one, and obviously, this router will loop back to address 1, so that will be a hop away. For that, we should go and use neighbour one and evgp multi hop two, so you should count how many hops away your peer is, and then you can use this multi VGP multi hop command. Finally, we can go and use the password with the neighbour command. So for that, we have the neighbour password, and for example, Cisco, we have other options as well that, if you want to change the keep-alive timer, we have discussed that the default keep-alive is 60 seconds and one-eighth of a second is the whole down timer. But suppose if you want to use an aggressive timer, we can go and use timers BGP 30 and 90, and in that case, we can go and set the BGP timers. Alright, so let’s stop here, and in the next section, we’ll perform the lab exercises or whatever we have covered in this section.