Hi, hello again, this is Habib Korea. And we are sort of continuing with our topic number two with the introduction of BGP. And so far we have covered very good content. But now we are trying to establish the practical side of BGP and how we will go about doing those neighboring adjacencies between the routers using BGP. So in my short break, what I did is basically I introduced BGP, and I brought up the routers in the topology, as you can see, and I have configured the interfaces with the IP addresses on them and, and it the routers don't have anything except the IP addresses that I have given them. So I also introduced a loopback interface which is loopback zero in every router.

So one dot one dot one dot one, nine If provided one dot one dot one dot one, and as a loopback interface for r one, I've given the serial interfaces IP addresses based on their location 192 168 dot 12 dot 112, meaning it's between r one and r two. So that's how I will. I'm defining the interfaces between between the routers. I hope that it's clear and I will bring up now our tos configuration as well. Let me see if I have it here. Yep, sorry about that are two Yep.

So same thing show IP interface brief. So same thing are our two has basically is neighboring three routers, which is r one, r r five As well as our three. So and those are the IP addresses I have given. Yes, so 25 dot one dot one dot one is the interface for FA zero slash zero that is that is adjacent to our five. And the two serial interfaces 13 dot two is the interface that's facing r three. And serial interface one slash two is the interface facing r one.

And basically once I did that, let's look at our for show IP interface brief. And our four is in the same same spot as all the other routers I have the loopback address, and I have the two interfaces that are facing Basically our ones in r one and r three. Okay, so I hope that makes clear. And let's bring our three. Again, our three is the same thing we are actually looking at three here. Sorry, what happens when you're rushing, okay, so r three is basically neighboring r four.

And that's the IP address I have given to the serial interface one slash zero. And it's also neighboring. Our to our choose serial interface is his one slice zero and I believe that's the IP address that we have given our three and the on the other side it is 192 168 dot 13 dot two. That's the IP address of the interface s slash one slash zero. Now, once you do that, once you do the point to point connectivity, what I will do is basically try to ping the interfaces that are that are that are neighboring the routers and the way I would know if everything is okay if I do show CDP neighbor, I can see the neighboring interfaces and the routers that are neighboring are three. Okay, and I do know from my actual output from our two, what's the IP address of those interfaces and I can actually ping them.

So if I do ping 192 dot 168 dot 13 dot dot 13 dot two. As you can see, I can ping archers serial one slash zero interface. So that's the introduction of this topology. gonna take a little bit of a little bit of a break here and I will come back again and start doing the neighboring adjacencies between the routers. So first of all in this topology we will cover the ibgp okay neighboring and then we will come back to ebgp and introduce that into the same topology okay so we are covering few things here that are really important please follow up there will be three commands that we will be using in the end to verify if BGP is has established in this topology. One is the show IP BGP summary.

The other command is show IP BGP neighbor and neighbors and of course, show IP BGP and show IP route. Okay, so Okay, I'm back here and what I did is basically trying to put two two consoles in the screen just to so they so that anyone could follow me properly here. And so we will introduce the BGP here. So let's do that. So So, so router BGP, right, and we set it as 100. So we'll give it 100.

Same thing here we'll do the same router BGP, hundred. Now, with this first of all, we will be introducing the loopback interface into BGP. So, so that's what we will be advertising. So network one dot zero dot zero dot zero. Okay, and then we will. So there will be a neighbor and IP address of the neighboring interface which is going to be here 192 dot 168 dot 12 dot two.

Okay. And then we'll say to remote as hundred. Okay, so that's the that's the command that are required for the BGP neighboring advertisement. So router BGP, hundred, then the network that you want to advertise in the routing domain for the BGP, which is network one dot zero dot zero dot dot zero and then the neighboring IP address of the router next to the of the of the router that is adjacent remote as and the AAS number Okay, which is 100. So that's what we needed here between the two. Now same thing we will do here on the other side our BGP and the network that we will be and the network that we will be advertising will be two dot zero dot zero dot zero.

And the neighboring device is going to be 192 168 dot 12 dot one remote as hundred they are bought into the same they're the boat routers are in the same as domain. Okay, so that's it. So we have already formed adjacency as you can see neighboring device. Now our one is also neighboring our four, right so we have to do that as well. In here. So command is same neighbor 192 168 dot 14 dot two, remote as hundred.

Now our two is also neighboring our three neighbor 192 168 dot I believe I've given it twice Three dot 23 dot one. Let me verify. Okay, so it's 192 168 dot 13 dot dot one remote as hundred. Let me save that. Now let's move on to our three. I just brought up the console for our three, router BGP, hundred.

And we will first advertise the loopback interface which is three dot three dot three dot zero. dot zero dot zero and the neighboring device IP address is going to be 192 168 dot 213 dot two remote as hundred neighbor 192 168 dot 43 dot one remote as hundred here. So that's the, that's the remote IP of the our four interface. And I believe that's all we need to do here in our three. Save it let's bring the interfaces in the IP The r three now let's introduce router BGP and our four network for the 00. Neighbor 192 168 43 to remote as hundred.

Now as you know, also our four is neighboring r1. So neighbor 192 168 dot 14 dot one remote as hundred So basically I believe we have stablish the ibgp configuration and peering. So let me let me just bring up here r1. So if I do show IP BGP summary as you can see our one is neighboring two routers, which is good. So that's how we will verify the summary. And if I go to our to show IP BGP summary.

Archer is also neighboring to two routers. If I go in To our three, show IP, BGP summary, same thing, our threes neighboring two devices. And if I go to our for show IP BGP summary, I can see two neighboring devices here as well. So with this we conclude that we can actually establish the neighboring agencies using BGP. And so, so what we did is actually configured neighboring adjacency within the same as environment within the same as administrative distance. Now, there are a few things I wanted to basically bring up that that we need to understand clearly here is that for some reason, if we look at the IP route information in r1, if I do show IP route right to only in r1.

As you can see, what we see here is the is the loopback address of our two which is great and the loopback address of our four as you can see, but I do not see the loopback address of our three and this is what I was trying to explain that with the split horizon rule r1 is not really picking up the IP or the loopback address or any networks from r three. If I go to r two I see the same thing if I do show IP route, show IP route here in r two. I can only see the the loopback address Which is for router three as you can see, and I'll be seeing the loopback address of r1 as you can see, but I do not see anything that's coming from our four. And if I go to our four, if I do show IP route, same thing, I don't see anything coming from.

So if I look at our four it will be seeing any it will see our three. As you can see any can see our four. Yeah. Our three and our one it can see our three and our one. D means BGP. So those two, but it does not see our two.

So this is very important to understand why is this happening? The reason why this happened Because BGP needs to have full mesh neighboring done otherwise it will not communicate with the with the routers that are adjacent to them and get those IP routes. So basically to to mitigate this kind of a problem, there are different processes and procedures that we need to get into. But for BGP, full mesh is required if you don't want to basically utilize other methods. So for that reason, what we need to do in order for basically r1 to see our three is add another neighboring relationship between r one and r three and that is basically the key to Get all the information from our three as well. Okay, so let's do that for one example.

And let's see if it makes a difference. So, if I go to r1 Let me bring our three as well right. So if I do show IP interface brief and r1 is here, so if I do show so let me just go call t router we know which BGP router, autonomous system we are adding this relationship to. So if we do remote, and I can do 192 dot 168 dot one dot sorry, 13 dot one remote as hungry And if I do hear the same thing, neighbor 192 dot 168 dot 12 dot one remote as Congress. Now if I do a show IP BGP beacon network Okay, so I'm I'm was looking at the the routing table and it seems like it was just taking time to establish the neighboring between r one and r three. So as I said the full mesh needs to be done with all the with all the adjacent routers and also the routers that are behind the edges and routers to stablish those kind of neighboring relationship and they could read it each other's routing tables and get updates from their from the other routing tables.

So, under under our three I will be able to see our one as you can see that the interface that's for r one r two and r four for r three. So, so, this is I hope this is clear, we will have to do for all the routers, but as you know that is administratively time consuming. So, we will move on to the next topic which is explaining the the summary of the of the BGP forwarding table right. So, in here if I do show ibgp I will see there is There are the different statements here that are coming. So, so asterik means this asterisk here, this actual asterisk means that the entry table is valid. Okay?

The greater sign here means means that this is the best entry for a given prefix. Okay? So for this, this and this, these are basically the best entries for these networks here. Okay and it tells you what's the next hop network which is 12 dot one dot 214 dot 212 two sorry, 14 dot two from our ones perspective, okay. And as I was saying to you is that it is basically Add vector as you can see, it gives us the autonomous system here 100 100 and then this is the next hop here which is the weight weight is one of the attributes of BGP. Okay, so same thing if we go and look at basically our force table our force neighboring table which is show IP BGP neighbor, I, I don't know why it's why the Yeah, so.

So that's one of the commands that you could use for, for identifying the neighbors. And if you Everything is okay with the with the neighboring. So there's the neighbor stuff. That's the neighbor in more details, it tells you what's the router ID, router ID is basically giving me the loopback address of the of this remote router, and so on. The other command is show IP BGP. And the same thing I'm seeing here is that the best path is basically given here asterik.

And, and it's a valid entry. Greater sign means it's the best entry for this prefix best entry for this prefix best entry for this prefix. I mean, it's BGP ibgp these are the AAS numbers. Here's 100 and 100. And by the way, so with this, we conclude the part two of the have our second topic here. And in our next lecture, we're going to join the we will complete the configuration of we will complete the configuration to connect our two with our five okay and we will establish ebgp