WEBVTT

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All right, so now we are going to dive into discussion on configuration and verification

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of OSPF version 2. So, that is for IPv4. The topology we're going to work with today looks

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like this. So, we need to make sure we are aware of the boundary points of where we're

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enabling OSPF versus where we're not. So, as I was describing yesterday, when you look

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at the topology, something like this means OSPF is running here, OSPF is running here,

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but it's not running here. So, I'm only going to be configuring on those two interfaces

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for R1. R2, we're configuring it here, we're configuring it here, we're configuring it

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here, but not here or here. So, that's going to be important for the certification exam

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just to make sure you recognize those boundary lines. So, that way you're not configuring

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it on the wrong interfaces, because if you do, you might have a bad config, a poor config,

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or they might just simply say, well, you weren't supposed to configure it there, so you don't

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really understand what you're doing. And as a result of that, well, we're going to have to

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give you zero on this particular question or simulation or whatever it happens to be,

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because we don't really know how they grade everything. That's a very well-kept secret

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in the world of certification exams for Cisco. So, we just have to assume that if we don't do

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exactly what they say, they're going to penalize us for that when it comes to the certification

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exam. So, with that said, let's begin right now by taking a peek at, do we have OSPF running at

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all? And the answer to that is no. Just before class, I went ahead and I disabled OSPF on all

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of my devices. So, if I type in Show IP Protocols, you'll see there's nothing here related to OSPF.

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So, if you go to every single device, OSPF has been disabled. So, nothing there for OSPF. It

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would actually say OSPF in the output. So, there's nothing here listed. It's just the running

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protocols application. So, that'd be like for software-defined networking features and stuff

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like that. So, we won't get into that right now. Oops. Oh, I should have never highlighted that.

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Show IP Protocols. Right. Again, nothing running there. And same thing with branch. So, we don't

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have OSPF running at all. So, the first thing I want to do is I just want to focus on R1 right

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now so we can understand the steps and procedures we need to go through. So, first of all, I'm going

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to create a routing process. And for OSPF v2, we type in the keyword of router. Then we type in

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OSPF. And then it asks us for our process ID. So, this process ID is just a locally significant

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identifier for the OSPF process. That's it. So, this is something that does not have to

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match on all the other routers. For those of you with EIGRP experience, you type in router,

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EIGRP, and then you actually specify what is called an autonomous system number. So,

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let me just show you that. You'll see how it says autonomous system number for EIGRP.

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That is a number that has to match on all the routers that are going to be sharing information

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with each other. So, if I was configuring EIGRP in this environment, that number would have to

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be the same in all the routers. But for OSPF, it does not have to be the same in all the routers

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because it's a totally different thing. It is a process ID instead. What does that mean? It means

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on my router, I can run multiple OSPF processes. So, I could have like process one for something.

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I could have process two for something else. When might you see that typically? With, for example,

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like a service provider. A service provider might have multiple customers connected up to them.

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So, for example, let's just say this is a service provider router up top, R1. Then I might have a

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customer connected here. I might have a customer connected here. If that's the case, and I was

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running OSPF with those customers, I would want to make sure that there's two different OSPF

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processes, one for each customer. That way their OSPF, let's say process one, is for that customer,

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and OSPF, let's say process two, is for that customer. And that'll make sure that those

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processes are kept isolated and separate from each other. In addition, we want to do things

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like VRFs and everything else, which is not part of this discussion. We'll talk about that later on.

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But in the end, right, by having different processes, then I could have different instances

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of OSPF running on my device for isolation purposes. So, the key here is, is that you're

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going to pick a number that's locally significant for you and your device for OSPF, and it doesn't

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have to match on every other router. It doesn't have to. I like to make it match just for simplicity

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sakes for my brain. So, I'm just going to pick OSPF process ID one. All right. So, now what I

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want to talk about, now that it's enabled on the device, and if you type in something like do show

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IP protocols, you'll see that it is now running. OSPF process ID number one. Notice here there's

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something called the router ID. We mentioned that router ID a multitude of times yesterday.

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We saw the router ID was in the packet header or the OSPF header, I should say.

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And what did we say the router ID was for? The router ID is a number that uniquely identifies

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this router to all the other OSPF routers. Now, when you look at that, it looks like,

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it feels like, it tastes like, I won't stick out my tongue, I promise you. All right. It smells like,

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smells like an IPv4 address. It totally does. But what you need to learn here is that it is not

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an IPv4 address. It is a router ID. And your router ID can be any number from 0001 all the

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way up to 255, 255, 255, 255. That is your range for router IDs. You cannot do 000. And the reason

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why is because 000 actually shows up in your database as the default route. And it's an actual

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identifier for that default route and it can cause conflict. So that's just one of the reasons why

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you can't use 000. All right. But other than that, you can use any other number as your router ID.

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So what is a router ID? A 32-bit number that uniquely identifies that router to all the other

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routers in the OSPF environment. And you saw the router ID is going to be in our what? OSPF header.

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So for every message our router sends, it puts the router ID in it.

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Now, how is this router ID chosen? Okay. The router ID is going to be chosen in one of three ways.

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So what the router does first is it looks to see if you manually configured the router ID.

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Well, I think we all know that I did not manually configure the router ID because you never saw me

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manually configure the router ID. If I wanted to manually configure the router ID, I would use the

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router ID command and then put in the router ID that I want to use in dotted decimal notation.

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32-bit number in dotted decimal notation, any number in that range from 0001 all the way up

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to 255, 255, 255, 255. If I do that, that is what's going to be used.

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If I don't do that, then the router has to dynamically figure out what the router ID is.

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And so what do we have on our routers that are also 32-bit numbers, folks?

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What else do we have on our routers that are also 32-bit numbers? Chat in.

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Well, not interfaces, not loopbacks. Okay, what do we have that is a 32-bit number?

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IP addresses, exactly, right? An IP address. So since an IP address is a 32-bit number,

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could the router use one of those as its router ID? Yes, of course it could. Of course it could.

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So that's what it does. It looks for the IP addresses that are configured on this device.

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And where do we configure our IP addresses? On interfaces. So if we type in do show IP

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interface brief, there's the IP addresses that are configured on this device.

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So here's what it does first. It says, well, since Raymond has not configured the router ID,

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because it knows that I'm the one who configures it, Raymond, right? Of course.

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Since Raymond has not configured the router ID,

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then I need to look at the IP addresses that have been configured on this device.

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And figure out what I could use as the router ID. I just need a 32-bit number.

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So first though, it looks for what? It looks for loopback interfaces. Okay,

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what is a loopback interface? A loopback interface is a virtual interface

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that you can configure on your router and give it an IP address.

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And then that loopback interface is reachable through any of the other interfaces on the device.

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So think of a loopback interface like a centralized IP address on the device

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that can be reached through any other interface and is always up,

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up as long as one other interface is up, up on the device.

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So it's going to look for loopback interfaces first.

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Then it's going to go ahead and say, if there's a loopback interface,

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I will use the IP address of that loopback interface. So in this case,

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there's no loopback interface, right? So since there's no loopback interface,

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what does it have to do? It has to then look at all the other interfaces that are on the device

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that have IP addresses. And in this case, it has chosen what? The highest. It's going to choose the

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highest IP address of those interfaces. So in this case, you can see it is going to choose the

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highest. It's 203.0.1.13.90.

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All right, 203.0.1.13.90. There you go. So if I configure the router ID,

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such as router-id, we'll go 0.0.0.1 as an example.

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We're going to pick that R1. I'm going to use 0.0.0.1 just to keep it simple for us as we

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explore our device. Do show IP protocols. You'll see in this case, I'm now using 0.0.0.1.

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Now, I did not have to restart the OSPF process in this case because I don't have any

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neighborships right now. If I had any neighborships, then I would have to force

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OSPF to reset itself. And you do that by typing in clear IP OSPF process. Now,

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it will tell you to do that, meaning that if you have changed the router ID and you already have

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neighborships, it'll say you've got to clear the OSPF process. So you type in this command,

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you're good to go. All right, let's go over to R2 and try to demo this a little further.

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Show IP route. No, show IP interface brief. All right, so take a peek at this. I've got

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one loopback address right now, 10.2.2.2. Let's go ahead and create another loopback.

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Oh my gosh, I'm having so much trouble typing today. Oh my goodness, what is going on? All right,

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focus. All right, router. Oh, no, interface, interface, interface, loopback, 192. My brain's

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all over the place. IP address, 192.2.2.2.2. All right, let's go ahead and try this again.

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192.168.255.125.255.255.255.255. All right, so now let's go ahead and take a look at do show IP

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interface brief. So now you'll see here that we have our interfaces with IPs and we have two

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loopbacks. So let's go ahead and type in router OSPF1. So all I've done is enable OSPF. We haven't

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set the router ID on R2, but what I want to point out to you is that the router says, hey, did you

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configure router ID? No, you didn't. Okay, so now let's look for loopbacks. Oh, look, we've got two.

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Which one has the higher IP address? That's it. Whichever one has the higher IP address is the

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winner. So the router ID should be 192.168.255.1 in this case. Do show IP protocols. And you'll see

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here that it is 192.168.255.1. So remember this for the exam. If it's not manually configured with

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the router ID command, then what happens? The router looks for loopback interfaces.

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If there is one loopback interface, that's the IP it uses. If there's more than one loopback

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interface, then it's going to use the highest IP address of those loopback interfaces.

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If there's no loopback interfaces, then it's going to use the highest IP address

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of the remaining interfaces. All right, so now there was a chat that came in that says,

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so it'll choose the highest IP address unless the interface is down. That's a good question.

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Not something that would come up on the certification exam, all right? What I've

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just told you up to this point is what you want to know for the exam. But you know what I think

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is a really good idea? Let's test that right now, right? Let's go ahead and test that.

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Let's go to branch. Let's type in show IP interface brief. What is our highest IP address?

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It's this one right here, correct? Let's bring that interface down and see if it still uses it.

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Let's just test it and see what happens. So, configure terminal, interface, gigabit Ethernet

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0 slash 1. And let's go ahead and type in shutdown. So, then we'll take a look at the

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output of show IP. Oops, I got to... Okay, so let's try this. 198.51.100.46 is now down, down.

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Let's enable OSPF. Okay, so look at this. This one is down, administratively down, right?

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This one, the next highest is down, down. This is going to be fun. So, let's see which one it picks

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when it's all said and done.

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Again, not something you're going to have to go this deep on the certification exam,

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but take a peek at that. The interface has to be up. Wait, we got a loopback? Oh, you're right,

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we've got a loopback. So, that was the winner. I didn't even notice the loopback there.

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Yes, Casey, you said right, the loopback would be the winner. You're right.

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So, the loopback destroyed me in that demonstration there. All right, no problem.

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This is easy. Let's do this.

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Let's also bring down the loopback. How does that sound? So, what I'll do is I will remove OSPF.

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No router OSPF 1, so that's gone. Let's go ahead and type an interface loopback.

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1, 2, 9, it looks like. 1, 2, 9. Let's go ahead and shut it down.

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So, now we'll see that the highest IP is down. The loopback is down. The next highest is down.

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So, let's see if it's still using that loopback even though it's down.

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But you have 1716. Who's 1716? All right, take a peek at that. So, here's the moral of the story.

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It won't use the loopback. It won't use the loopback. It won't use the loopback.

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But you have 1716. Who's 1716? All right, take a peek at that. So, here's the moral of the story.

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It won't use it if it's administratively down, but it'll use it if it's down-down.

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For the exam, I wouldn't worry about that. For the real world,

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maybe something you care about, but to be honest with you, I don't care.

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Why? Because you should always manually configure your router ID.

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Because when you manually configure a router ID, is there any chance it'll dynamically change on

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you? Yes or no? No. So, with that in mind, isn't that the better option to go with? Absolutely,

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that is the better option to go with in a production environment. But for the exam,

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right, knowing stuff like you see on this page for the router ID,

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it could be manually configured with the router ID, right? Let me just write up here 32-bit.

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That's all it is, a 32-bit number, manually configured. If not, then it goes through this

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process, right? In addition, as we saw, if the interface is administratively down, it won't use

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it. But if the interface is down-down, it'll still use it. Now, exactly. Another thing

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I want you to be well aware of is that OSPF is about what? It's about learning information

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so you can do what? So, you can build your routing table. Let me repeat that in case you

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blanked out. What is OSPF all about? Learning and sharing information so you can populate your

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routing table. So, does the router ID have to be something that is routable? Does it have to be

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something that's in your routing table? No, of course not. Remember how OSPF works. We are going

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to be enabling routing for OSPF on this device, specifically on the interfaces. And after I do

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that, I form neighbor adjacencies. Once the neighbor adjacencies is done, what do we say?

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We're going to exchange LSAs. So, this router here sends out its link state advertisement.

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For example, the type 1 LSA. What does R2 do with that? R2 makes a copy of that LSA

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and then it floods it out all ports participating in OSPF. So, it makes a copy of it and floods

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it out. So, if I got one in and I have two ports, I got to copy it twice and send it out to my

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neighbors. So, when they get it, they're receiving a copy of the original, okay? Unmodified. An

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unmodified copy of the original. So, this happens from neighbor to neighbor to neighbor to neighbor.

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This happens before routing even happens, right? So, routing is not even set up yet in my environment.

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But when I start enabling my interfaces, the fact that I send an LSA to my neighbor,

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it makes copies of it and sends it to its neighbors who makes copies of it and sends

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it to its neighbors, the flooding process. That is how, in the end, they learn and then they

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populate their routing table. So, the router ID is not something that has to be in your routing table.

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The other day, I got an email and that was the question I got, right? Well, the router ID,

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why is that? Well, you know, why all of a sudden when we changed it in the lab? It was a CCNA

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question. We changed it in the lab, but it's not in the routing table now. How in the world does

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that work? Okay, well, the router ID doesn't have to be in the routing table because you're not

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using it for routing. You're using it as an OSPF identifier so you know who's who and what they

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know and what they're flooding. So, right now, we have what? We have, for example, on R1, what's

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my router ID? 0001. Will I ever find that in the routing table? No, because that's not even a valid

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IP address. You can't even put that as an IP address on any interface. That is an invalid

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IP address. Just like what? Router ID 255, 255, 255, 254 is an example, right? Is that an invalid

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IP address? Possibly. No, it is. Absolutely, it is, right? Because that's in the class E addressing

00:22:30.920 --> 00:22:38.920
space. But it's a valid router ID. It's a valid router ID. So, don't let that throw you off. Don't

00:22:39.640 --> 00:22:44.280
think that it has to be in the routing table. Never. Absolutely not. It's a router ID. All right.

00:22:44.280 --> 00:22:47.560
Now that we got that out of the way and you're able to answer questions on the exam about it,

00:22:49.719 --> 00:22:53.079
in case you said, that's why I'm a fan of using an invalid IP address. Same with me.

00:22:53.640 --> 00:22:58.599
I'm like, I might as well use things that are not even IP addresses as my router ID. So,

00:22:58.599 --> 00:23:03.479
for documentation purposes, it's so much easier for me. Makes so much more sense when it's all

00:23:03.479 --> 00:23:09.160
said and done, right? Because now I can label this router as 0001. I can label this one as 0002,

00:23:09.160 --> 00:23:16.199
003, 004, 005, 006, 7, 8, 9, 10, 11, 12, 30, right? Let's just do that. That's easy for me. I like

00:23:16.199 --> 00:23:19.959
that. I really do. That's my preference. You don't have to do it that way, but that's my preference,

00:23:20.920 --> 00:23:25.400
right? And based on documentation, that's how I know each router. And then when I look at my

00:23:25.400 --> 00:23:31.079
database later, my database is going to be showing me information based on router ID. So,

00:23:31.079 --> 00:23:34.119
I know, oh, that's router one, that's router two, that's so-and-so, that's so-and-so,

00:23:34.119 --> 00:23:37.079
that's so-and-so, right? Based on my document, easier for me as an admin.

00:23:39.000 --> 00:23:43.239
All right. So, now that we've got that done, what do we want to talk about next? We want to

00:23:43.239 --> 00:23:50.599
talk about the fact that we have to now start enabling the routing process on interfaces.

00:23:50.599 --> 00:23:59.560
So, enable OSPF on interfaces. So, right now, OSPF is enabled globally,

00:23:59.560 --> 00:24:03.640
but it's not doing anything. It is literally not doing anything

00:24:05.719 --> 00:24:12.359
because I have to have at least one interface participating in OSPF for this whole thing to

00:24:12.359 --> 00:24:21.560
get started. So, let's focus on Gigabit Ethernet 050. So, why would I want to enable OSPF on

00:24:21.560 --> 00:24:27.319
Gigabit Ethernet 050? All right. A couple of different reasons. So, reason number one,

00:24:28.520 --> 00:24:42.199
so I can join multicast group 224.0.0.5. That is the all OSPF routers multicast

00:24:42.199 --> 00:24:46.920
group, right? So, I join that multicast group. What can I do now on that interface?

00:24:47.479 --> 00:24:55.800
I can send plus receive hellos to form neighborship.

00:25:00.199 --> 00:25:03.959
So, I enable the routing process on the interface, so I can join that multicast group and then,

00:25:03.959 --> 00:25:09.000
too, send and receive hellos so we can form neighborships. So, I enable on this interface.

00:25:09.000 --> 00:25:12.599
I can send you hellos. I enable it on this interface. You can send me hellos.

00:25:14.439 --> 00:25:18.119
And then, what are those states we go through? We said down, init, two-way.

00:25:18.119 --> 00:25:23.000
Down, init, two-way. And then, xstart, exchange, loading, full.

00:25:24.280 --> 00:25:28.680
So, what do we do after that? We then have the ability to sync with each other.

00:25:28.680 --> 00:25:40.760
So, why? Sync with each other, essentially share info. So, why do we enable the routing process

00:25:40.760 --> 00:25:46.040
on the interface? So, we can form neighbor adjacencies and share information. Okay. But

00:25:46.040 --> 00:25:51.400
there's another reason why we do this, and most people are not taught this. I teach it in CCNA.

00:25:51.400 --> 00:25:58.040
I teach it here. And this is probably even more important than what we've just talked about here,

00:25:58.040 --> 00:26:06.199
in my opinion. Why? Because what we're doing is we're injecting network ID

00:26:10.439 --> 00:26:17.560
of interface into link state database,

00:26:19.160 --> 00:26:24.199
injecting the network ID of interface into the link state database. So, the network ID

00:26:24.199 --> 00:26:32.040
of this interface gets put into my link state database. Why is that important? Why is that

00:26:32.040 --> 00:26:44.199
important? Because I need to tell you about all the networks I am connected to, as well as

00:26:44.199 --> 00:26:50.359
everything else I've learned from other devices. So, if I'm not injecting my own network IDs

00:26:50.920 --> 00:26:56.040
into OSPF, you would never know that I'm directly connected to that network.

00:26:58.280 --> 00:27:01.239
And if you don't know I'm directly connected to the network, how do you build?

00:27:01.880 --> 00:27:09.319
What? How do you build? What's that thing that we have with OSPF? A topological map.

00:27:09.319 --> 00:27:21.880
So, same thing is true about EIGRP, except you're not building a topological map with EIGRP, right?

00:27:21.880 --> 00:27:26.520
But with EIGRP, you enable the routing process on interface, the network ID gets injected into

00:27:26.520 --> 00:27:31.079
the topology table for EIGRP, and now you can tell the other routers, yeah, this is what I'm

00:27:31.079 --> 00:27:35.400
connected to. But now your neighbor is the only one who knows that, but at least your neighbor

00:27:35.400 --> 00:27:43.319
knows that, and it learns about those networks from you. All right. So, let me show you how we

00:27:43.319 --> 00:27:48.359
enable the routing process on an interface and all this magic happens. So, what we're going to do,

00:27:48.359 --> 00:27:51.959
first, we're going to type in do show IP interface brief.

00:27:56.280 --> 00:27:58.839
And then we're going to type in interface gigabit Ethernet.

00:27:59.719 --> 00:28:04.119
What are we doing? Zero size zero on our one right now? Perfect. All right. So, gigabit Ethernet,

00:28:04.119 --> 00:28:07.880
zero size zero, we're going to enable the routing process on this interface, and it's up, up. If

00:28:07.880 --> 00:28:12.359
your interface is not up, up, then it's not going to be able to participate in the OSPF process.

00:28:12.359 --> 00:28:17.400
It'll be enabled on it, it just won't participate because it's down. So, any interface that is down,

00:28:17.400 --> 00:28:21.560
the network ID doesn't get injected into OSPF. So, it's got to be up, up for the network ID to

00:28:21.560 --> 00:28:29.000
get injected into OSPF. There is nothing here listing multicast addresses. So, right now,

00:28:29.000 --> 00:28:34.359
we're not part of the group 224005. We're going to see this change here momentarily.

00:28:35.079 --> 00:28:41.719
If you look at the IP addressing space, it's 240.23.0 slash 30 is the network ID. That's

00:28:41.719 --> 00:28:46.040
what it would be. So, that's what we're going to find in our link state database after.

00:28:46.599 --> 00:28:51.719
So, right now, let's type in do show IP OSPF interface. This will tell us what interfaces

00:28:51.719 --> 00:28:55.479
are participating in the routing process, and you'll see no interfaces are participating in

00:28:55.479 --> 00:29:03.959
the routing process. And if we type in do show IP OSPF database, you'll see there's nothing right

00:29:03.959 --> 00:29:10.520
now in our OSPF database either. It's empty. The only thing we see is my router ID.

00:29:13.800 --> 00:29:18.520
Uh-oh. There we go. That took a little bit of time to update. All right. A little networking

00:29:18.520 --> 00:29:24.119
lag there between my systems. Hopefully, that doesn't last all day. But you'll see right there

00:29:24.119 --> 00:29:31.160
how we have right now an empty database. So, first thing we're going to do is we're going to

00:29:31.160 --> 00:29:40.359
go to interface gigabit ethernet 0 slash 0, and we're going to type in IP OSPF 1 area 0. I'm

00:29:40.359 --> 00:29:43.959
starting to think I don't have a typing problem. I think there's a lag problem right now with me

00:29:43.959 --> 00:29:48.359
in the demo environment because this is a demo environment that's somewhere else where we have

00:29:48.359 --> 00:29:53.160
all of our racks set up, and I might be having a connectivity issue with it today as we just saw

00:29:53.160 --> 00:30:01.239
with the lag. So, maybe I'm not typing that bad. We'll go with that story. All right. So,

00:30:01.239 --> 00:30:06.839
now that the interface is enabled for OSPF, let's type in do show IP OSPF interface brief.

00:30:07.479 --> 00:30:11.000
We'll see that we have this interface participating in the routing process now,

00:30:11.000 --> 00:30:19.160
gigabit 0 slash 0, a part of OSPF process ID 1. It's in area 0, right? Area 0. That's what I

00:30:19.160 --> 00:30:24.439
typed in there. So, I enabled that interface, put it in area 0. That's its IP address. That's

00:30:24.439 --> 00:30:30.199
its mask. That's the cost. Right now, it's going through the DR BDR election process. That's why

00:30:30.199 --> 00:30:34.760
it says wait. And you'll see it's still going through that process. It's about a 40-second

00:30:34.760 --> 00:30:39.400
process. Once that's done, it has elected itself as a DR. So, we'll come back and talk about that

00:30:39.400 --> 00:30:44.280
later on today what all of that means if you're not familiar with that. All right. But now,

00:30:44.280 --> 00:30:50.920
I want to take a look at my database, do show IP OSPF database. Whoa. Look at that. What are we

00:30:50.920 --> 00:30:54.760
looking at? We're looking at the type 1 LSA that I briefly introduced you to yesterday.

00:30:55.319 --> 00:30:59.000
That's a type 1 LSA. How do I know? Because it says router link state. That's what that means,

00:30:59.000 --> 00:31:03.959
type 1. More on that later today. We'll actually talk about those LSAs later today. But notice the

00:31:03.959 --> 00:31:10.920
link ID is 0001. That's my router ID. Notice that the advertising router is me, 0001. Look at the

00:31:10.920 --> 00:31:18.839
link count, one. One link. One of my interfaces is participating in OSPF. That's what that means.

00:31:18.839 --> 00:31:22.920
One of my interfaces is participating in OSPF. Let's crack this open.

00:31:29.160 --> 00:31:40.119
There you go. I have injected the network ID of that interface into OSPF locally.

00:31:41.800 --> 00:31:47.640
For me. So, what does that mean now? It means when I form a neighbor adjacency with somebody,

00:31:47.640 --> 00:31:55.880
I will send them this information. And they will now know that I am connected to this network.

00:31:56.520 --> 00:32:01.719
Remember, we said a bunch of puzzle pieces, right? Bunch of puzzle pieces that all have to

00:32:01.719 --> 00:32:07.479
be put together to build the puzzle. Puzzle piece, that's all it is. All right. What about our other

00:32:07.479 --> 00:32:15.560
interface? Gigabit Ethernet, 0 slash 1 in our diagram up here. Okay, let's do that one. Interface,

00:32:15.560 --> 00:32:27.959
Gigabit Ethernet, 0 slash 1. IP OSPF 1, area 0. Let's take a peek at our database now.

00:32:28.760 --> 00:32:34.760
Crack it open. Now both of them are in there. So, you see, by enabling the routing process

00:32:34.760 --> 00:32:42.040
on an interface, you inject the network IDs into your link state database, into your type 1 LSA.

00:32:42.040 --> 00:32:45.800
So, that way there, when you form neighbor shifts with other routers, you can tell them, hey,

00:32:45.800 --> 00:32:50.839
I am R1, and these are the links that are directly connected to me.

00:32:52.920 --> 00:32:59.719
So, if every router does this, and every router gets this information, then they have the ability

00:32:59.719 --> 00:33:03.319
to put puzzle pieces together. Now, there's more than just the type 1 LSA. That is part of the

00:33:03.319 --> 00:33:08.599
puzzle building process. But this is your most fundamental LSA, the most important one, the one

00:33:08.599 --> 00:33:14.760
that starts building everything, and the one that uses Dijkstra's shortest path first algorithm

00:33:14.760 --> 00:33:19.560
calculation every single time in its most aggressive form that it can possibly be done in.

00:33:20.920 --> 00:33:26.839
That's what you're dealing with in this case. So, remember we talked about multi-area, right?

00:33:26.839 --> 00:33:37.160
Why multi-area? Because this LSA will never go over here. Type 1 LSAs never cross area border

00:33:37.160 --> 00:33:43.160
routers. More on that later, and you'll understand why that is. Now, you might be saying, well, then

00:33:43.160 --> 00:33:47.160
how do you get from here to there? Okay, because of other LSAs. You got to learn all, you got to

00:33:47.160 --> 00:33:51.880
learn about five of them here for the exam. I'll teach you all five today. This is just one of them

00:33:51.880 --> 00:34:06.520
so far. All right. So, now that we have that done, let's go over to DSW1. And on DSW1, we are going to

00:34:07.640 --> 00:34:14.600
enable OSPF on gigabit 1 slash 0 slash 13. And as soon as we do that, folks,

00:34:14.919 --> 00:34:21.800
we are going to do what? Form a dynamic neighbor adjacency. Why? Well, if we go back to R1

00:34:22.520 --> 00:34:29.959
and we type in do show IP interface gigabit Ethernet 0 slash 0. Notice how I have now joined

00:34:29.959 --> 00:34:38.360
multicast group 224005, the all OSPF routers multicast group. So, that means I'm sending

00:34:39.239 --> 00:34:52.199
hello packets now. Do show IP OSPF hello. No. Do show IP OSPF packet hello. No. All right. Show.

00:34:53.080 --> 00:34:57.719
Oh, no. Debug. I meant to type in debug. Debug IP OSPF hello. That's what I should have typed.

00:34:57.719 --> 00:35:02.040
There you go. So, you'll see I'm sending out a hello packets out my interfaces.

00:35:03.000 --> 00:35:07.959
There you go. So, I sent one out gigabit 0 0. I sent one out gigabit 0 slash 1.

00:35:13.399 --> 00:35:20.120
Every 10 seconds by default. So, they're going out, but DSW1 isn't configured yet.

00:35:20.679 --> 00:35:26.199
So, if we go to DSW1 right now, and we go to interface gigabit 1 slash 0 slash 1,

00:35:26.679 --> 00:35:35.800
and we type in IP OSPF 1 area, what? Area 0. Remember, area has to match. Area has to match.

00:35:35.800 --> 00:35:42.840
Okay. Type that in. We should see here. Boom. We just went from a net down to a external exchange

00:35:42.840 --> 00:35:49.239
loading full. We're good to go. We just went through the whole thing. We're full on. We're

00:35:49.239 --> 00:35:55.000
down to a external exchange loading full. We're good to go. We just went through the

00:35:55.000 --> 00:36:03.479
whole thing. We're full already. That was fast, wasn't it? Woo. That was way faster

00:36:03.479 --> 00:36:08.360
than yesterday when I explained it to you in, what, 45 minutes? All those different stages.

00:36:08.760 --> 00:36:17.719
But now, let's go back to R1. And on R1, if we look at the output of show IP OSPF database,

00:36:17.719 --> 00:36:26.919
what are you going to see? Whoa. I've got information from someone else now. Someone else.

00:36:29.320 --> 00:36:33.800
I don't like that router ID. Let me show you what happens if I change it after a neighborship.

00:36:34.120 --> 00:36:46.520
So, what we're going to do is we're going to type in router OSPF 1, router ID 0.0.0.3. So,

00:36:46.520 --> 00:36:51.959
we're going to go 1, 2, 3, 4, 5. That's what we're going to do today.

00:36:55.479 --> 00:36:59.000
It's telling me, remember what I said, you're going to have to clear the OSPF process because

00:36:59.000 --> 00:37:05.879
there's already a neighborship. Let's do that. Yes, I want to do that. You'll see this

00:37:05.879 --> 00:37:09.719
neighborship is going to flap. And then we're going to reform our neighborship.

00:37:10.600 --> 00:37:13.560
And then once our neighborhood is reformed, we'll see over here on R1,

00:37:13.560 --> 00:37:21.080
now we're going to learn from 0.0.0.3.

00:37:21.080 --> 00:37:38.439
Come on. My impatience with OSPF runs strong today.

00:37:38.840 --> 00:37:51.719
Okay. There we go. Just patience. That's all it takes. So, I'll go back to R1. You'll see now

00:37:52.600 --> 00:38:01.320
0.0.0.3. And notice what it says. I have one link. So, if I open up the database right now in R1,

00:38:01.320 --> 00:38:07.080
and we look at R1's database, and we look at the information inside of it,

00:38:07.080 --> 00:38:13.479
especially the information from who? From DSW1. It'll say that that interface is participating

00:38:13.479 --> 00:38:21.239
in the routing process. This one right here. And it has a certain IP address on it. Well, R1

00:38:21.239 --> 00:38:27.399
then says, hey, I have an interface in that same network. So, that means we are connected together.

00:38:27.399 --> 00:38:31.399
But I also know we're connected together. Why? Because we're neighbors. Right? So,

00:38:31.399 --> 00:38:35.719
because we're neighbors, I already know that. But I know that this is what you call it. That's

00:38:35.719 --> 00:38:39.320
what I call it. We're there. We can now build our quality, and we can share that information

00:38:39.320 --> 00:38:44.520
with other people now. Other routers, I should say. But something I want you to realize is,

00:38:44.520 --> 00:38:48.120
remember how we say everybody's got to be synchronized in the area? So, all four of

00:38:48.120 --> 00:38:54.040
these routers in area 0, they're going to end up with the exact same database for area 0.

00:38:55.080 --> 00:39:02.439
Go to DSW1 right now and type in show IP OSPF database. They're the exact same. Just pay

00:39:02.439 --> 00:39:17.080
attention to this. Look at this. R1, DSW1. R1, DSW1. R1, DSW1. That's pretty incredible.

00:39:18.760 --> 00:39:24.120
All right. Let's refresh this. Right now, they're perfect, except for the age timer.

00:39:24.120 --> 00:39:30.360
The sequence numbers were off a bit. Let's try that again. Get that there. Get that there.

00:39:30.360 --> 00:39:34.520
There you go. The sequence numbers were off a bit because they weren't fully, fully synchronized,

00:39:34.520 --> 00:39:38.120
but now everything should be normal. Yep, there you go. Now, they're fully synchronized. Look at

00:39:38.120 --> 00:39:42.439
that, except for the aging timer, and that's okay. Everything else is the exact same.

00:39:43.800 --> 00:39:49.399
That's what is required in an OSPF area. If there's ever a tiny discrepancy in any of these

00:39:49.399 --> 00:39:55.080
values except for the age, then that means you're not synchronized properly. And that is that,

00:39:55.080 --> 00:39:58.520
because that means the routers are not seeing the topology the exact same way, which means you have

00:39:58.520 --> 00:40:02.199
something wrong somewhere that you're going to have to figure out. All right. Great news is,

00:40:02.199 --> 00:40:05.959
on the exam, you're not going to be digging this deep into the database to figure that stuff out.

00:40:05.959 --> 00:40:08.840
But I'm just trying to give you a real-world picture of OSPF.

00:40:10.280 --> 00:40:14.120
Every one of those routers have to have the exact same database, same information,

00:40:14.120 --> 00:40:17.560
right down to sequence numbers, checksums, all of that stuff.

00:40:20.520 --> 00:40:25.080
Let's go ahead and enable this interface now on DSW1, gigabit 1.0.0.14.

00:40:29.080 --> 00:40:43.719
All right. Take a look at my database now. You'll see it now says two for DSW1.

00:40:44.760 --> 00:40:47.320
Why? Because now we have those two interfaces participating in the

00:40:47.320 --> 00:40:49.639
routing process with those two different network IDs.

00:40:50.600 --> 00:40:56.760
Just like if we now type in do show IP OSPF interface brief, you're going to see,

00:40:56.760 --> 00:40:59.800
there they are, 13 and 14, participating in the routing process.

00:41:00.040 --> 00:41:03.399
That link count should match what you have locally configured.

00:41:04.760 --> 00:41:09.479
I go to R1 now, right? Update the database. You'll see it now says two as well.

00:41:10.199 --> 00:41:14.040
Why? Because we exchanged LSAs. We've updated each other about that information.

00:41:14.679 --> 00:41:18.840
All right. But watch this. Are you ready? What is this network right here?

00:41:18.840 --> 00:41:25.719
What is this network right here? Okay. It is listed as 10.40.23.4.30.

00:41:28.280 --> 00:41:32.360
Is R1 directly connected to that? No, it's not.

00:41:33.719 --> 00:41:41.239
Has R1 learned about that? Yes. Why? Because DSW1 injected that information

00:41:41.399 --> 00:41:50.199
because DSW1 injected that network ID into its database and it shared that information with R1.

00:41:50.199 --> 00:41:54.040
So if I go to R1 and I type in show IP route,

00:42:12.040 --> 00:42:20.040
there it is. So R1 knows how to get there because DSW1 told it.

00:42:24.040 --> 00:42:32.040
That's how OSPF works everywhere. Everywhere. So when we have OSPF running here eventually,

00:42:34.040 --> 00:42:38.600
R1 will learn about that through link state advertisements.

00:42:38.679 --> 00:42:46.919
It'll learn about this network both from DSW2 and from R2. Because don't forget R2 is part of

00:42:46.919 --> 00:42:54.120
that network. R2 will send out an LSA and say, hey, I belong to that link, that network. DSW1,

00:42:54.120 --> 00:42:59.719
DSW2 does the same thing. So R1 then says, okay, you're both, you're both telling me the same

00:42:59.719 --> 00:43:05.479
thing. That means you two are connected together. That's how R1 is going to be able to figure that

00:43:06.360 --> 00:43:12.040
out. Yeah. Pretty cool when you think about it that way. So all these different pieces of the

00:43:12.040 --> 00:43:15.879
puzzle, the database come together and then R1 can say, okay, so you're connected to that,

00:43:15.879 --> 00:43:20.199
you're connected to that. What's the quickest way to get there? Is it quicker to go this way

00:43:20.199 --> 00:43:26.439
or is it quicker, let's say, to go this way? Well, obviously it'd be quicker to go this way

00:43:26.439 --> 00:43:32.439
because it's only one link to get there. If I go this way, it's two links to get there.

00:43:32.520 --> 00:43:37.239
If I go this way, it's two links to get there. So based on cost,

00:43:37.800 --> 00:43:42.679
R1 will install the path this way in the routing table to get here.

00:43:45.159 --> 00:43:51.639
It's learned about it two different ways, but in the end, both OSPF, meaning administrative

00:43:51.639 --> 00:44:00.120
distance is the same. And then through metric, it figures out that going this way is faster.

00:44:00.120 --> 00:44:02.280
Therefore, it puts that one in the routing table.

00:44:14.679 --> 00:44:22.439
Now, let me ask you this question. Do we need to enable OSPF on our SVIs?

00:44:23.159 --> 00:44:29.800
Yes or no? I mean, because think about it. Join the multicast group,

00:44:30.360 --> 00:44:34.760
send and receive hellos, so that way there I can synchronize with routers.

00:44:44.600 --> 00:44:49.959
What do you think, folks? Do I need to enable OSPF on my SVIs?

00:44:52.919 --> 00:44:56.520
I mean, is there anybody I need to form a neighbor adjacency with?

00:44:59.320 --> 00:45:05.479
No. Therefore, do I have to join the multicast group to send and receive hellos?

00:45:06.760 --> 00:45:14.919
No. Do I have to share any information with anybody out those SVIs? No.

00:45:14.919 --> 00:45:35.639
No. But the answer is yes. You need to enable OSPF on the SVIs. Why? Why? Because of number four.

00:45:36.600 --> 00:45:45.239
Inject the network ID of, oh, it says off, of interface, there you go, into the link state

00:45:45.239 --> 00:45:55.239
database. How is R1 going to learn about my networks? If the interfaces are participating

00:45:55.239 --> 00:46:04.520
in the routing process, that's how R1 is going to learn. I need the network ID injected into OSPF.

00:46:05.479 --> 00:46:08.520
Okay. So, enable the routing process on the interface. Let's look at this.

00:46:10.439 --> 00:46:23.000
Interface, VLAN 10, IP, OSPF, one, area zero. Let's take a look at the database here on DSW1.

00:46:23.639 --> 00:46:31.639
It now says three. Let's go take a look at R1 and see if it learned. It now says three. Let's

00:46:31.639 --> 00:46:40.600
crack that open, though, on R1. So, we'll type in router 0.0.0.3. Let's look at router three's

00:46:40.600 --> 00:46:48.679
information while we're on router one. And, oh, my gosh, look at that. Boom. I now know about what?

00:46:50.120 --> 00:46:57.800
The network ID of the SVI. So, if I type now in, we have a conflict here, don't we? We do. Okay.

00:46:57.800 --> 00:47:03.320
Hang on a second. Show run pipe to include IP route. I think we have a conflict here. We do.

00:47:03.320 --> 00:47:08.439
Okay. Hold on. Administrative distance conflict. I got to get rid of this from our last session.

00:47:08.439 --> 00:47:13.479
I remember configuring that. So, no IP route. That was a static route, remember? All right.

00:47:13.479 --> 00:47:18.280
So, pretend that wasn't there. It wasn't there. Okay. So, let's look at our database right now.

00:47:18.280 --> 00:47:25.080
And, look, we know about 10.0.0.0 slash 24. So, if we take a look at a routing table now,

00:47:25.080 --> 00:47:36.919
show IP route, it's magic. There it is. OSPF 10.0.0.0 slash 24 out gigabit ethernet 0 slash 0

00:47:36.919 --> 00:47:44.520
because that's the best way to go right now. That's why we enable the routing process on the SVIs.

00:47:44.520 --> 00:47:59.479
So, interface VLAN 20. Oops, wrong button. There we go. Interface VLAN 50. Interface VLAN 200.

00:48:01.479 --> 00:48:04.679
Now, let's go back to R1 as an example. Take a look at the database.

00:48:05.560 --> 00:48:10.679
The database should now say, let's try that again. Look at just the database.

00:48:11.000 --> 00:48:20.280
We'll see it now says six for DSW-1. Six interfaces. The four SVIs plus gigabit 13 and 14.

00:48:20.280 --> 00:48:30.520
That's what that means. Let's crack that open. And you'll see SVI, SVI, SVI, SVI.

00:48:31.320 --> 00:48:38.679
SVI. There they all are in our routing table now.

00:48:45.239 --> 00:48:50.199
If this is the first time in your life you've seen OSPF explained to you this way,

00:48:50.360 --> 00:48:54.360
let me know, please.

00:49:07.159 --> 00:49:11.320
Right. And when it's explained this way, it makes a lot more sense, as John said.

00:49:11.320 --> 00:49:14.360
So, that's how it really works. Yeah, that's how it really works.

00:49:15.959 --> 00:49:19.159
It's really how it works behind the scenes. Okay.

00:49:21.000 --> 00:49:27.719
So, what does that mean? It means I have to go to every single interface in our topology

00:49:28.439 --> 00:49:31.080
and just keep enabling interfaces. That's what I've got to do.

00:49:32.760 --> 00:49:37.879
That's how you do it. And then once you have all the interfaces you want participating in

00:49:37.879 --> 00:49:41.080
your routing process, then all your routing tables are going to be updated,

00:49:41.639 --> 00:49:44.679
as long as you configured it properly. So, let's continue going through this,

00:49:44.679 --> 00:49:48.679
because there's a few more things I have to show you. So, don't fall asleep on me just yet, folks.

00:49:49.639 --> 00:49:52.280
Don't fall asleep on me just yet, because if we go to DSW-2,

00:49:55.560 --> 00:49:59.479
I have to show you another way that you can enable OSPF on interfaces.

00:50:03.479 --> 00:50:11.080
So, the way I've shown you right now is what we call the interface enable command.

00:50:11.080 --> 00:50:19.000
So, if we go back to DSW-1 as an example, I type in do show IP OSPF interface gigabit

00:50:19.000 --> 00:50:25.320
ethernet 1.0.0.0.13. You see what it says? I enabled it, even though it says attached via,

00:50:25.320 --> 00:50:32.040
I enabled it using the interface command. That's what that means. What's the interface command?

00:50:32.040 --> 00:50:39.639
IP OSPF, the process ID, the area you want the interface in. That's the interface command.

00:50:40.439 --> 00:50:47.000
But there's another command that exists. Does anybody know what that command is, that you can

00:50:47.000 --> 00:51:07.560
use? Yes, it's the network command. The network command. The network command. So, I'm going to

00:51:07.560 --> 00:51:16.600
type in configure terminal router OSPF 1. I'm then going to type in router ID. Let's set that

00:51:16.600 --> 00:51:25.479
up first. 0.0.0.4, because I said 1, 2, 3, yep, 4. Now, the network command is right here in router

00:51:25.479 --> 00:51:38.439
OSPF configuration mode. Router OSPF configuration mode. Look what it says. Put in a network number.

00:51:38.439 --> 00:51:45.560
All right. Let's just put in 0.0.0.0, just for learning purposes.

00:51:45.959 --> 00:51:48.919
Let's put in a question mark. It says wildcard bits.

00:51:56.600 --> 00:52:00.199
Folks, where else do we hear the term wildcard bits?

00:52:00.199 --> 00:52:01.159
Wildcard bits.

00:52:06.919 --> 00:52:16.919
Access control lists. What do wildcard bits allow us to do?

00:52:16.919 --> 00:52:31.719
All right. They allow us to specify a range of IP addresses.

00:52:33.959 --> 00:52:40.120
That's right. In an access control list, when you have the network number first,

00:52:41.080 --> 00:52:50.679
and then the wildcard mask combined, they identify ranges of IP addresses. Notice,

00:52:50.679 --> 00:53:01.080
I did not say subnets. No. Ranges of IP addresses and nothing more.

00:53:02.040 --> 00:53:13.239
So, what do you think this does, then? Specifies a range of IP addresses and no more. So,

00:53:14.040 --> 00:53:18.040
let me put in a wildcard mask of all 255s.

00:53:20.840 --> 00:53:26.040
What range of IP addresses is that, folks?

00:53:26.360 --> 00:53:35.959
Everything. Yes. Everything. So, I am telling the router right now,

00:53:36.919 --> 00:53:44.439
find every single IP address on this router. There they are.

00:53:44.919 --> 00:54:07.159
And then, enable OSPF on those interfaces. Let me repeat that. Look for every single IP address

00:54:07.239 --> 00:54:15.719
on this router and enable OSPF on their interfaces. So, what area, though? Now,

00:54:15.719 --> 00:54:22.360
I got to specify the area. This command is not done yet. Area zero. Now, for EIGRP,

00:54:22.360 --> 00:54:27.560
if you're EIGRP fans and you use EIGRP, you're familiar with the network command,

00:54:27.560 --> 00:54:32.199
but it's only this long for EIGRP. That's it. Just what I've highlighted. And it means the

00:54:32.199 --> 00:54:39.080
same thing. It means the exact same thing. Look for what? All IP addresses on the router,

00:54:39.080 --> 00:54:42.600
enable OSPF. So, let me do that right now. Boom. Now, we're going to see a lot of

00:54:42.600 --> 00:54:45.639
neighborhoods that are formed here. We'll talk more about this a little bit later.

00:54:46.199 --> 00:54:52.360
But what I want to point out to you is we type in do show IP OSPF interface brief. We're going

00:54:52.360 --> 00:54:57.080
to see that I have OSPF enabled on all of the interfaces that had an IP address, no matter what.

00:54:57.959 --> 00:55:03.719
Every single one of them. So, we grab our interface list.

00:55:05.959 --> 00:55:11.959
And I type in do that. There you go. Every single one of them.

00:55:14.280 --> 00:55:21.800
Now, the question is, is this really? Is this really what you want to do? The answer is

00:55:21.879 --> 00:55:31.399
absolutely not. No. Absolutely not. This is not a recommended best practice. What I just did.

00:55:31.399 --> 00:55:37.320
If you did this on the exam, Cisco would frown considerably at you and mark you incorrect.

00:55:39.000 --> 00:55:47.320
Because you have just said, going forward, from here on out, if any interface is created

00:55:47.320 --> 00:55:53.399
on this device, with any IP address, it automatically participates in OSPF, no matter

00:55:53.399 --> 00:56:03.479
what.

00:56:15.800 --> 00:56:19.959
Here we go. I created an interface. It's now participating in OSPF.

00:56:19.959 --> 00:56:26.840
That is a no-no because of security reasons. Yeah. It's kind of reckless to do that. I would

00:56:26.840 --> 00:56:33.399
have to agree with that statement. Even with passive interface, Joshua, not worth it. Okay?

00:56:33.399 --> 00:56:38.280
Not worth it. Doesn't matter. I will talk about passive interface and why it's really important.

00:56:38.280 --> 00:56:44.520
But no matter what, you really don't want interfaces enabled if they don't need to be

00:56:44.520 --> 00:56:50.600
enabled. What does that mean? It means this version of the network command is not acceptable

00:56:52.760 --> 00:56:59.639
on a certification exam or potentially in the real world for you. Keep that in mind.

00:56:59.639 --> 00:57:04.520
All right. What does that mean? It means that you need to look at your interfaces,

00:57:05.159 --> 00:57:10.280
especially on the certification exam, and you need to identify which of the interfaces need

00:57:10.280 --> 00:57:16.439
to be enabled. All right? Now, I showed you the interface command, for example, on DSW1 and R1,

00:57:17.080 --> 00:57:21.879
and that one was pretty straightforward, right? IP, OSPF, just go to each interface and do this.

00:57:22.679 --> 00:57:29.080
But what if Cisco says you're not allowed to do that? You must use the network command. Or what

00:57:29.080 --> 00:57:33.479
if you're troubleshooting a scenario that is using the network command? That's why I have to teach

00:57:33.479 --> 00:57:37.239
you this. I prefer the interface-level command myself. That's what I use in production

00:57:37.239 --> 00:57:40.679
environments. That's what I use in the real world. I really am not a big fan anymore of the network

00:57:40.679 --> 00:57:45.320
command. When I have something that is better, more specific, and gives me 100 percent control

00:57:45.320 --> 00:57:49.399
of what I'm trying to do. But the network command, I can accomplish the same thing.

00:57:51.239 --> 00:57:56.520
But if I can do with the network command the same thing that I did on the interface command,

00:57:56.520 --> 00:58:00.120
I might as well just use the interface command because then I know that interface, that interface,

00:58:00.120 --> 00:58:04.360
that interface based on the configs is enabled for that. But let me show the network command.

00:58:04.439 --> 00:58:09.239
So let's look at another example. If we said network, for example, now,

00:58:09.239 --> 00:58:17.399
and I said 10.0.0.0, what if I put a wildcard mask of 0.255.255.255?

00:58:19.639 --> 00:58:21.399
Okay, what does that actually mean?

00:58:23.800 --> 00:58:29.719
Okay, what does this actually mean? So Conrad, yes, 0.0.0.255.255.255 is considered reckless.

00:58:30.199 --> 00:58:36.600
But let's get better. Let's get non-reckless, right? So in this case, this is every single

00:58:36.600 --> 00:58:49.000
IP address from 10.0.0.0 to 10.0, no, 10.255.255.255. Now, if you don't know how I did that,

00:58:49.959 --> 00:58:55.560
I will teach you wildcard masking and shortcuts so you can do that in your brain for the certification

00:58:55.560 --> 00:58:59.879
exam. So I'll teach you that during our ACL discussion, not here right now during OSPF,

00:58:59.879 --> 00:59:03.239
because we've got so much more to cover than to teach you how to read this, okay?

00:59:04.360 --> 00:59:07.879
But when you learn that in ACLs, you can come back and this will make more sense if you struggle

00:59:07.879 --> 00:59:16.360
with this. But this is every single IP address from 10.0.0.0 to 10.255.255.255, area 0. So that

00:59:16.360 --> 00:59:22.520
means it'll be every single one of these addresses except for this one, because that address doesn't

00:59:22.520 --> 00:59:28.840
fall in that range. This address does not fall in that range. So if we look at the output now,

00:59:31.560 --> 00:59:44.360
we'll see that everything's there that starts with 10, 10.0.0.0 to 10.255.255.255. So the 192

00:59:44.360 --> 00:59:50.040
is no longer there, the 172 is no longer there. But again, not good enough, because in our scenario,

00:59:50.040 --> 00:59:54.679
what interfaces do I want participating in the routing process? I want this interface,

00:59:54.679 --> 01:00:03.159
this interface, and my four SVIs. I don't want these ones right here at all. Oops, too many.

01:00:03.159 --> 01:00:10.520
I don't want these ones here at all based on my scenario. So again, right, not good enough,

01:00:10.520 --> 01:00:16.120
not good enough. So we could keep playing around with this and trying to get as creative as

01:00:16.120 --> 01:00:22.840
possible to accomplish our objective. But there's really two Cisco approved,

01:00:23.399 --> 01:00:31.080
recommended ways of accomplishing this. Andrew, I'm going to come back and talk about that. You

01:00:31.080 --> 01:00:37.639
got to be careful with that word summary in this case. All right, because this has nothing to do

01:00:37.639 --> 01:00:45.399
with summarization, or summarizing networks, or anything like that. It purely just says,

01:00:45.399 --> 01:00:51.000
enable OSPF on these interfaces, inject their network IDs, and share those network IDs with

01:00:51.000 --> 01:00:56.439
everybody. There's no summarization going on whatsoever. No summarization going on whatsoever

01:00:56.439 --> 01:01:02.199
in that case. That's not what the network command does, right? I've seen documentation where it

01:01:02.199 --> 01:01:08.600
says the network command tells you to advertise this network. No, it doesn't, right? That was

01:01:08.600 --> 01:01:14.199
something that was written in books a long time ago in the world of RIP, V1. And yes,

01:01:14.199 --> 01:01:20.280
that made sense for RIP V1 back in the 80s and early 90s. That's right, I said 80s and 90s.

01:01:21.080 --> 01:01:26.520
Okay, that's not how it happens today. It hasn't been that way for 30 years approximately,

01:01:26.520 --> 01:01:31.719
maybe, yeah, about 30, 27 years, okay, with the advent of variable length subnet masking.

01:01:31.719 --> 01:01:37.320
And with that case, it is purely straight up. Find the IP addresses, enable it on those

01:01:37.320 --> 01:01:42.520
interfaces, inject their network IDs, and, right, so we'll talk about summarization later today.

01:01:44.600 --> 01:01:50.840
So, and we do that totally different. And this is true for EIGRP and OSPF. Both of those

01:01:50.840 --> 01:01:57.399
would be the same application for that concept. All right, so Cisco's recommended best practice,

01:01:57.399 --> 01:02:01.560
so these are really your two options for the certification exam. If they tell you,

01:02:02.439 --> 01:02:07.399
we want you to enable the routing process, let's say, on this interface using the network command,

01:02:07.479 --> 01:02:16.840
okay, two options for that. Option number one is to use a network ID and a wildcard mask

01:02:17.479 --> 01:02:23.639
that matches that exact range of IP addresses for the subnet. So, when you look at this particular

01:02:23.639 --> 01:02:30.679
subnet of slash 30, a slash 30, okay, what would the IP addressing space be for this particular

01:02:30.679 --> 01:02:40.120
network? So, what network is this? This is going to be network 10.40.23.12 slash 30, right? So,

01:02:40.120 --> 01:02:45.560
even though it says 14, remember, that's the IP address of the interface. So, what network does

01:02:45.560 --> 01:02:53.159
that belong to? Well, based on my diagram, it's dot 12. So, let's put that in here.

01:02:53.560 --> 01:03:03.239
We'll put in 10.40.23.12, and the wildcard mask that would match a slash 30

01:03:07.080 --> 01:03:13.879
is what? No, sorry, I put the wrong number there. Three, there you go, three. Yes, Andrew,

01:03:13.879 --> 01:03:22.120
good job typing that in. Perfect. Okay, so there. So, this is every IP address from 10.10.23.12

01:03:23.399 --> 01:03:32.439
to 10.10.23.15, and it should be not 10.10, it should be 40, right?

01:03:33.959 --> 01:03:42.280
40, yeah, thank you. Let's look at that. Right, so that says look for every single IP address

01:03:43.239 --> 01:03:52.040
in that range. Now, always remember this, you can only have one IP address on that router

01:03:52.679 --> 01:03:58.199
in any given subnet. Did you know that? Yeah, that's true. So, if you have a Cisco router or

01:03:58.199 --> 01:04:06.199
a multi-layer switch, you can only have one interface on that router in any given subnet.

01:04:06.199 --> 01:04:10.919
You cannot put two interfaces on a single router in the same subnet.

01:04:11.320 --> 01:04:15.239
Okay. So, with that in mind, that means when you type in this command,

01:04:15.800 --> 01:04:24.280
even though it's a range of addresses, there could only ever be one match on this router.

01:04:27.320 --> 01:04:31.879
That's it. Because if you try to add another interface on this router in that same range,

01:04:32.679 --> 01:04:38.280
it would yell at you and say, nope, cannot do it. One interface on this router,

01:04:38.280 --> 01:04:45.800
cannot do it. One interface per subnet on your router. So, if we look now at the output,

01:04:45.800 --> 01:04:49.320
a show IPOSPF interface brief, you'll see that one interface has been enabled.

01:04:52.360 --> 01:05:00.439
What about this interface here as an example? So, 10.40.23.10, that is actually in the .8 network.

01:05:00.439 --> 01:05:07.479
So, let's do the same command, but let's change this to a .8. So, if we had .8.0003,

01:05:07.479 --> 01:05:14.600
then that would mean everything from 8, 9, 10, 11. And so, the interface is what? The interface is

01:05:14.600 --> 01:05:21.080
10. So, it falls within that range. So, let's hit enter there, and we'll see that the end result is

01:05:21.080 --> 01:05:28.360
we are now participating in the routing process. Okay. So, that is one option. Specify the network

01:05:28.919 --> 01:05:35.560
ID range of addresses, because then it would only match one and one interface. That's it.

01:05:35.560 --> 01:05:39.159
That's the recommendation. So, the recommendation nowadays, it's been this way for a long time,

01:05:39.159 --> 01:05:45.000
but I say nowadays, is when you use a network command, it should only affect one interface.

01:05:45.000 --> 01:05:47.879
Okay. Well, if I'm using the network command and it only affects one interface,

01:05:48.439 --> 01:05:55.879
why don't I just use the interface command instead of typing in a network command for

01:05:55.879 --> 01:06:00.360
every interface? I mean, I have to type in the same number of commands, don't I? Sure. Yeah.

01:06:00.360 --> 01:06:08.520
But that is the recommendation. Okay. What is the other option we have? This is a lot easier.

01:06:08.520 --> 01:06:16.120
Why not just specify the actual IP address? So, for example, I want this interface participating

01:06:16.120 --> 01:06:21.959
in the routing process. So, what do I do? Why not just say, hey, find this IP address,

01:06:22.840 --> 01:06:29.719
and whatever interface it's on, enable it for OSPF. How do you do that? That's really simple.

01:06:29.719 --> 01:06:35.639
Use your network command, type in the IP address of that actual interface, so 10.0.0.2,

01:06:36.199 --> 01:06:42.439
and then put 0.0.0.0. Now, I'm not even messing around with wildcard mess,

01:06:43.000 --> 01:06:48.840
and then I type in the area number, and boom. It looks for that exact IP address, and when it

01:06:48.840 --> 01:06:54.600
finds that exact IP address, it enables it on that interface. So, that is another option you have

01:06:54.600 --> 01:06:59.399
that would be perfectly acceptable on the certification exam. Cisco will be very proud

01:06:59.399 --> 01:07:06.120
of you if you use that option or the option of the network. The question is, you know,

01:07:06.120 --> 01:07:12.120
what is going to be accepted, whatever they tell you to use? If they tell you to use the exact IP

01:07:12.120 --> 01:07:16.760
address, then you better use this option. If they tell you to use a range of IP addresses,

01:07:16.760 --> 01:07:24.439
then use the network ID and craft a wildcard mask for that. Yeah. All right. So, I'm just

01:07:24.439 --> 01:07:29.000
showing you the different options because if it shows up on the exam, right, are they really

01:07:29.000 --> 01:07:36.360
testing you on real-world awesome knowledge? Not really. Not in my opinion. In this case,

01:07:36.360 --> 01:07:39.000
they're testing you on, do you know the difference between the network command and the interface

01:07:39.000 --> 01:07:42.840
command and how to use a wildcard mask? That's really what they're testing you on, which to me,

01:07:43.800 --> 01:07:47.320
it doesn't matter for the real world. It doesn't matter. That doesn't prove your skills, right?

01:07:47.320 --> 01:07:49.800
But they could do that to you, and I want you to be ready for that.

01:07:54.679 --> 01:08:01.800
Hey, it's getting good. It's getting good. Let's keep going. Let's go to R2. Now, I'm going to go

01:08:01.800 --> 01:08:05.080
a lot quicker here, right, folks? Because I've gotten everything out of the way that I want to

01:08:05.080 --> 01:08:10.040
cover in regards to the interfaces. So, right now, on Router 2, we have to be super careful now,

01:08:10.360 --> 01:08:15.800
and this is where you got to pay attention on the exam for Encore. What is this? Okay,

01:08:15.800 --> 01:08:20.919
this is going to be one of those area border routers. It's an area border router. Why? Because

01:08:20.919 --> 01:08:27.640
it has interfaces in area 0 as well as interface where? In area 1. You see that? You have to be

01:08:27.640 --> 01:08:32.600
super, super, super careful that you don't mess this config up because this is where you're going

01:08:32.600 --> 01:08:39.799
to get busted on the Encore exam. See, CCNA is single area, area 0. That's it. Encore is

01:08:39.799 --> 01:08:45.560
multi-area. So, you got to get this config right if you have to do it or troubleshoot it or anything

01:08:45.560 --> 01:08:55.000
like that. So, on R2, what do we do? Router-ID, because we already set up our process earlier

01:08:55.000 --> 01:09:03.160
when we were looking at the Router-ID, 0.0.0.2 today. Do show IP protocols. We'll see in our

01:09:03.160 --> 01:09:07.799
output here that we, yep, that's good right now. All right, let's get this party started.

01:09:07.799 --> 01:09:27.799
Interface, gigabit Ethernet, 0 slash 0, IP OSPF 1, area 0. Interface, gigabit 0 slash 1,

01:09:27.799 --> 01:09:34.919
IP OSPF 1, area 0. Now, for this one here, interface, fast Ethernet, 0 slash 1,

01:09:35.399 --> 01:09:49.080
0, IP OSPF 1, area 1. Do show IP protocols. Look at this. It says you are an area border router.

01:09:50.839 --> 01:09:57.319
Why? Because I have interfaces in area 1 and I have interfaces in area 0.

01:10:05.640 --> 01:10:08.359
What does that mean from a database standpoint now?

01:10:09.399 --> 01:10:15.959
Remember, your database has to be synchronized with every other router in that area.

01:10:18.120 --> 01:10:21.879
How is R2 even going to do that if it's connected to two different areas?

01:10:23.000 --> 01:10:32.439
Well, area border routers have a database for each and every single area. Let me repeat that.

01:10:32.439 --> 01:10:38.680
Area border routers have a database for each and every single area that they are connected to.

01:10:41.080 --> 01:10:48.200
So, if right now we type in do show IP OSPF database, here's the database for area 0.

01:10:51.240 --> 01:10:53.240
Now, we start a database for area 1.

01:10:54.520 --> 01:10:59.479
So, I'm going to have different LSAs for each and every single area.

01:11:03.399 --> 01:11:09.399
So, R2 now has to keep track of everything here, separate from everything here.

01:11:11.160 --> 01:11:16.040
This will all be synchronized together. This will all be synchronized together.

01:11:19.160 --> 01:11:23.000
And if you're still wondering, how do we share the information between areas? We'll get to that.

01:11:23.000 --> 01:11:29.319
We'll get to that. All right. Let's go to branch now. And in branch, I think we shut down some

01:11:30.279 --> 01:11:40.120
interfaces. We did some crazy things. So, do show IP interface brief.

01:11:47.799 --> 01:11:52.120
Let's type in interface. We have to bring this one back up.

01:11:52.120 --> 01:11:56.439
Interface.

01:12:01.160 --> 01:12:06.839
What other one did we shut down? Loopback 129. Let's bring that one back up.

01:12:09.479 --> 01:12:15.479
Router OSPF1. What else do we want to say? Router ID is going to equal 0.0.0.5.

01:12:15.560 --> 01:12:23.879
Okay. Do show IP protocols. Let's double check. OSPF is running, 0.0.0.5. Do show IP

01:12:25.000 --> 01:12:28.919
interface brief. Make sure all those interfaces I want up and running

01:12:28.919 --> 01:12:33.799
are up and running for right now. And I think we look good.

01:12:33.799 --> 01:12:48.279
Okay. So, let's go to branch right now, and let's purposely make a mistake to answer

01:12:49.160 --> 01:12:56.839
the question, would placing an interface in the wrong area generate a mismatch area ID message?

01:12:56.839 --> 01:13:01.240
Let's check it out. Let's do that here on purpose. So, interface, gigabit ethernet,

01:13:01.240 --> 01:13:12.279
0 slash 0, IP OSPF1 area. Let's say 0. See what happens. So, we got area 0 here. We got area 1

01:13:12.279 --> 01:13:25.879
here. I don't see anything yet on this router. Okay. On this router, though, I am getting an

01:13:25.879 --> 01:13:32.680
area ID. Yes. There you go. So, I am getting it on R2 right now. I'm not getting it on branch.

01:13:33.240 --> 01:13:36.439
Let's see if we type in do show logging if logging is turned on.

01:13:38.439 --> 01:13:45.160
Yes, it is. Okay. But it is quite possible we're not getting the log messages on branch

01:13:46.040 --> 01:13:53.240
because it is area 0, right? It is area 0, and that's area 1. So, I'm only getting the

01:13:53.240 --> 01:13:58.919
messages on the one that's area 1. So, this router thinks it's misconfigured where this

01:13:58.919 --> 01:14:04.919
router thinks it's not misconfigured because it's area 0. I think that's why we don't get

01:14:04.919 --> 01:14:09.959
the message on branch because it's area 0. It thinks it's right where this side thinks it's

01:14:09.959 --> 01:14:15.799
wrong because area 0 is always like it's the backbone. So, area 0 is like the best area. So,

01:14:15.799 --> 01:14:22.439
it's never wrong even though you might be wrong. So, let's go to branch, and let's fix that problem

01:14:22.439 --> 01:14:28.040
right now, and we'll just type in IP OSPF 1, area 1, and we'll see if now we form our neighbor.

01:14:28.040 --> 01:14:37.240
There you go. Problem solved. All right. Interface loopback 129, IP OSPF 1, area 1,

01:14:38.600 --> 01:14:40.200
and then let's not forget about

01:14:44.600 --> 01:14:48.359
our subinterfaces. So, we'll go to this interface here

01:14:48.759 --> 01:14:55.319
and type in the same command, area 1, and then we'll go to our other subinterface,

01:14:57.319 --> 01:14:58.759
and we'll type in area 1.

01:15:02.359 --> 01:15:10.919
So, with that said now, in the end, if I've done everything I needed to do on all of the interfaces

01:15:11.560 --> 01:15:18.680
properly, what we should ultimately have here in the end is branch A in its routing table,

01:15:19.240 --> 01:15:23.479
it has the SVIs from over here.

01:15:23.640 --> 01:15:24.359
Okay. Good.

01:15:31.959 --> 01:15:35.879
And what else? Any other interfaces. Look, all those other links too,

01:15:36.759 --> 01:15:40.279
all those other links in between that are participating in the routing process. Why?

01:15:40.279 --> 01:15:44.279
Network IDs injected into the link state database for all the different routers,

01:15:44.279 --> 01:15:47.479
and then the links between them are all being routed. So,

01:15:48.040 --> 01:15:52.680
are participating in the routing process. Why? Network IDs injected into the link state database

01:15:52.680 --> 01:15:57.319
for all the different routers. They send out their LSAs. All those LSAs go where they need

01:15:57.319 --> 01:16:01.080
to go to all the different routers they need to go to. The routers then take that information,

01:16:01.080 --> 01:16:05.319
build what they need to do, the topological map, the puzzle, if you want to call it a puzzle,

01:16:05.319 --> 01:16:10.279
with all the different LSAs, puzzle pieces, and then boom, they figure out what's the best place

01:16:10.279 --> 01:16:14.839
things to put in the routing table, and there you go. Now, if we go to DSW1, let's think about

01:16:14.839 --> 01:16:23.399
these networks here, right? These ones right here. DSW1 should now know about those.

01:16:24.919 --> 01:16:33.160
So, if we go to DSW1, and we type in do show IP route, there they are.

01:16:36.439 --> 01:16:41.959
Beautiful. Absolutely beautiful. And notice, it shows you the one size zero slash 14. Why?

01:16:41.959 --> 01:16:47.879
Because that's the best path to go. Will I have learned that I can possibly go this way as well?

01:16:47.879 --> 01:16:55.000
Of course, right? I know everything that's going on in this area. Everything. Meaning, I know I

01:16:55.000 --> 01:17:01.319
can go this way. I know I can go this way. I choose this way because it's shorter based on

01:17:01.319 --> 01:17:13.879
the cost, the metric. In this case, look at this. I'm load balancing for all of these. Okay.

01:17:14.600 --> 01:17:17.399
Here's a problem that I want to talk about next,

01:17:17.399 --> 01:17:21.720
since we have our entire environment configured. What is the problem?

01:17:22.680 --> 01:17:30.680
Well, right now, you see that network? Where is that network? Dot eight. It's right here.

01:17:32.680 --> 01:17:36.680
And who are we on right now? We're on DSW1. That's who we're on.

01:17:37.319 --> 01:17:42.040
So, we know that we can get there, gigabit one size zero slash 13.

01:17:44.839 --> 01:17:54.040
That makes sense, right? Yep. We also know we can get there from VLAN 20, 50, and 10.

01:17:56.839 --> 01:18:02.520
So, we know that we can get there from VLAN 20, 50, and 10.

01:18:02.839 --> 01:18:17.399
Okay. What about VLAN 200? Why is it not listed there? It's not listed there. Why?

01:18:20.359 --> 01:18:24.200
Because you can only load balance on four paths at a time.

01:18:24.439 --> 01:18:31.560
See what it says? Maximum paths is four for load balancing. Let's change that. Let's change that.

01:18:31.560 --> 01:18:38.600
Let's go to router, OSPF1, and let's say maximum paths is now going to be 10.

01:18:40.759 --> 01:18:47.640
Do you show IP protocols? We'll see that the now 10 equal path load balancing. Let's see if that

01:18:47.640 --> 01:18:54.120
changed my routing table. Oops, wrong button. Okay. So, let's go to the routing table.

01:18:54.200 --> 01:19:04.200
Yep. There it is. So, the reason why only four was showing up is because the maximum

01:19:04.200 --> 01:19:09.240
path for load balancing is four by default. But if there are more paths we could use,

01:19:09.240 --> 01:19:13.160
then we can get them put in there. All right. So, now, there we go. There's another one.

01:19:16.200 --> 01:19:21.640
Folks, is that a problem? Yes or no? Is this a problem?

01:19:24.680 --> 01:19:46.200
It is. Yes, without a doubt. Why? I want you to remember how traffic flows in and

01:19:46.200 --> 01:19:50.759
out of your subnet VLANs and broadcast domains. Think about it for a second.

01:19:51.560 --> 01:19:58.759
Your goal is to have traffic doing what? In and out, in and out, in and out, in and out.

01:20:00.520 --> 01:20:06.759
Right now, DSW1 is saying, I can go from here through the layer two network and back out.

01:20:08.759 --> 01:20:10.759
And we're only looking at this link right here.

01:20:11.720 --> 01:20:21.720
But what we need to be very careful of is that if we allow these two routers to form neighbor

01:20:21.720 --> 01:20:31.319
adjacencies, and we allow them to use that as a path under certain circumstances, that could crush

01:20:31.319 --> 01:20:36.919
that layer two environment from a performance standpoint. Watch this. Let's say this link went

01:20:36.919 --> 01:20:46.919
down. Let's say this link went down. The only way to get over here or over here or over here now,

01:20:47.720 --> 01:20:54.279
if traffic's coming in this way, is how? By using a layer two network.

01:20:55.240 --> 01:21:03.160
Or over here now, if traffic's coming in this way, is how? Through the layer two network.

01:21:03.959 --> 01:21:11.399
Oh my gosh, that is bad. You never want to allow that to happen in your environment.

01:21:12.759 --> 01:21:23.399
Never. That layer two network is purely for the traffic of those subnets, of those VLANs,

01:21:23.479 --> 01:21:32.359
of those broadcast domains, and no one else. Always remember that. So we actually do not want

01:21:33.319 --> 01:21:40.439
neighborhoods formed here, through that layer two environment. Because if we do,

01:21:40.439 --> 01:21:45.399
it could cause that issue down the road. Right? And if you're like, well, I want to use it as a

01:21:45.399 --> 01:21:50.200
last option, Raymond. Whoa. If you want to use that as a last option, you're designing your

01:21:50.200 --> 01:21:58.040
network incorrectly. Why not just add another link here? Or why not add more links? Add more

01:21:58.040 --> 01:22:05.799
links. Why not do something in here instead? Instead of using layer two as your path. Never.

01:22:05.799 --> 01:22:12.439
If you're down to layer two being your path to go from here all the way over to here,

01:22:13.560 --> 01:22:16.839
that's not a good design. That is like the worst thing you could have possibly done.

01:22:16.839 --> 01:22:22.359
So what do we have to do here? What do we have to do here instead?

01:22:23.799 --> 01:22:30.279
What we have to do is we have to stop the neighborhood from forming,

01:22:31.000 --> 01:22:36.200
but ensure the interfaces are still participating in the routing process.

01:22:37.160 --> 01:22:43.399
So let me ask you this, folks. How or what is used to form neighbor adjacencies?

01:22:46.839 --> 01:22:57.879
All right. Look, I have four neighbor adjacencies right now with DSW2.

01:22:57.879 --> 01:23:02.279
Four. I should have none in a well-designed network.

01:23:05.479 --> 01:23:11.399
Okay. What is used to form neighbor adjacencies? What is the packet called? What is the packet

01:23:11.399 --> 01:23:19.640
called? Well, it's not the LSA that's used to form neighbor adjacencies. What is used?

01:23:20.200 --> 01:23:32.919
Yes, the hello packet. So right now if we type in debug IP OSPF hello, I have hello packets

01:23:33.720 --> 01:23:40.520
going out. My interface is the SVIs. Look at the SVIs. Hello packets. Hello, hello,

01:23:40.520 --> 01:23:53.720
hello, hello, hello. What does that mean? It means that every single PC in that Layer 2

01:23:53.720 --> 01:24:00.200
environment has to receive those hellos and drop them as well. So wait a second. Not only are we

01:24:00.200 --> 01:24:06.759
forming neighbor adjacencies here, we're also sending hellos to devices that don't need them.

01:24:07.319 --> 01:24:13.640
What's another problem that could happen here? What if somebody adds a rogue router in that Layer

01:24:13.640 --> 01:24:19.240
2 environment? What if somebody installs a virtual router on one of their PCs because

01:24:19.240 --> 01:24:27.240
they're studying for the Encore exam? Could that possibly receive the hello

01:24:27.799 --> 01:24:37.959
and then form a neighbor adjacency with the production router and then inject false

01:24:37.959 --> 01:24:44.120
routing information into the routing environment and cause problems? Oh yeah.

01:24:45.959 --> 01:24:50.839
So what is one of the best ways to make sure none of that can happen? Well,

01:24:50.839 --> 01:24:57.000
how about we just stop the sending and receiving of hellos on those SVIs?

01:24:57.720 --> 01:25:04.439
And now I've just protected myself from rogue routers. I protected myself from suboptimal

01:25:04.439 --> 01:25:10.439
routing paths in certain scenarios and conditions. Yeah, let's stop the hellos. That's all we got to

01:25:10.439 --> 01:25:17.879
do. So stopping those hellos is going to be a security feature, really, in the end,

01:25:18.839 --> 01:25:22.919
as well as improve performance because we don't have to send this junk down there anymore

01:25:22.919 --> 01:25:26.680
and have all the PCs drop it anyways, and the phones drop it.

01:25:29.080 --> 01:25:33.959
So how do you do that? Joshua says passive interface. Yeah, watch this.

01:25:33.959 --> 01:25:36.439
I'm just going to type in right now, router

01:25:40.040 --> 01:25:46.600
OSPF1, right? So router OSPF1. There you go. You can see it. Now I'm going to type in passive

01:25:47.319 --> 01:25:53.399
interface default. What does passive interface default mean, folks? It means

01:25:57.879 --> 01:26:00.839
disable the sending and receiving of hellos on the interface.

01:26:05.319 --> 01:26:16.200
Done. All done. So what have I just done? No more hellos. No more hellos. No more hellos.

01:26:16.200 --> 01:26:27.720
No more hellos. No more hellos. No more hellos. Oops. Oops. We still need hellos there, don't we?

01:26:28.680 --> 01:26:34.279
Yeah, we do. So I'm going to type a no passive interface, gigabit ethernet,

01:26:35.479 --> 01:26:40.600
one slash zero slash 13. And now we'll send hellos out that interface again

01:26:41.240 --> 01:26:47.319
and form our neighbor adjacency. So for all those interfaces that go down your layer two devices,

01:26:47.319 --> 01:26:52.279
layer two network, make them passive. And this is one way to make every interface passive,

01:26:52.279 --> 01:26:55.959
passive interface default. And then you type a no passive interface for the interface you

01:26:55.959 --> 01:26:59.479
don't want to be passive. So there's now 14 is no longer passive either.

01:27:02.359 --> 01:27:07.240
So we type in, I'm going to type in do you all to shut off my debug and then

01:27:07.240 --> 01:27:10.040
do show run pipe to section OSPF.

01:27:15.319 --> 01:27:19.080
And you'll see here that I have passive interface default and then no passive interface for the

01:27:19.080 --> 01:27:23.080
interfaces I don't want passive. So here's something to keep an eye on the exam. If an

01:27:23.080 --> 01:27:27.640
interface is accidentally configured as passive, would that stop you from forming a neighbor

01:27:27.640 --> 01:27:38.839
adjacency? Yep. Right. So this is awesome. Now here's this is the actual way I recommend you do

01:27:38.839 --> 01:27:44.520
it in a production environment. Why is that? Because what I want to point out to you right now

01:27:44.520 --> 01:27:53.240
is that any interface now you enable for OSPF will not be able to form a neighbor adjacency

01:27:53.240 --> 01:28:00.600
with anyone else. That's right. At all. Unless you do what? Unless you also type in no passive

01:28:00.600 --> 01:28:06.120
interface for that specific interface. It gives you actually a little bit of extra security.

01:28:06.680 --> 01:28:12.120
Meaning that if an interface accidentally gets created with an IP address and it accidentally

01:28:12.120 --> 01:28:17.640
gets enabled for OSPF, it still won't be able to form a neighbor adjacency with anybody until

01:28:17.640 --> 01:28:22.680
you type in the no passive interface command. Because you're saying every interface is passive

01:28:22.680 --> 01:28:29.080
unless otherwise specified. So basically default deny unless explicitly allowed,

01:28:29.720 --> 01:28:36.359
which is pretty cool. So I like that as a real world option. I like that as a real world option.

01:28:36.359 --> 01:28:42.600
I do. So if you go to DSW2, I'll do the same thing on DSW2. So router config router. So we'll say

01:28:42.600 --> 01:28:47.959
passive interface default and then no passive interface gigabit ethernet one slash zero slash

01:28:47.959 --> 01:28:56.600
13 and 14. So same idea. Now we go over to somebody like our router over here, our branch

01:28:56.600 --> 01:29:01.720
router, right? Just to show you another example, you may not want to do passive interface default.

01:29:01.720 --> 01:29:05.720
So what if on the exam you weren't allowed to do that? Or it wasn't one of the valid options

01:29:05.720 --> 01:29:11.959
that you could pick in order to stop the sending and receiving of hellos on your sub interfaces?

01:29:11.959 --> 01:29:14.839
Well, then all you have to do is go into router OSPF configuration mode.

01:29:15.000 --> 01:29:19.000
And then just do it on an interface by interface basis. So you can just turn around and say

01:29:19.000 --> 01:29:25.240
passive interface fast ethernet zero slash zero slash zero dot 24. So you can just do it one at

01:29:25.240 --> 01:29:30.680
a time if you want to. So passive interface default says all interfaces and then you know

01:29:30.680 --> 01:29:36.200
pacify the interfaces you don't want to be passive. Whereas this one says all interfaces

01:29:36.200 --> 01:29:43.640
are not passive except these ones that I've typed in. So the other one, the one I showed you,

01:29:43.959 --> 01:29:47.640
the one I showed you on our distribution routers, this is a better option.

01:29:48.520 --> 01:29:53.160
This is a better option because it gives you that little added extra layer of security

01:29:53.160 --> 01:29:57.959
where this one doesn't. Because this one still ensures all interfaces are not passive.

01:29:57.959 --> 01:30:02.919
And so if somebody does connect or enable an interface, I should say for OSPF and so on and

01:30:02.919 --> 01:30:07.240
so forth, well then it can form a neighbor adjacency at that point in time because it's

01:30:07.240 --> 01:30:12.040
not passive by default. Whereas over here, it is all the interfaces are passive by default.

01:30:12.040 --> 01:30:17.080
Just something to keep in mind for the real world. All right, so do show IP protocols. You'll

01:30:17.080 --> 01:30:21.479
see that now when we look at this output, it even tells you what interfaces are passive on your

01:30:21.479 --> 01:30:25.479
device. So it tells you what interfaces are participating in the routing process,

01:30:25.479 --> 01:30:36.680
what interfaces are passive. We type in do show IP OSPF interface brief, we'll see all my

01:30:36.680 --> 01:30:40.520
interfaces that are participating, whether they're passive or not. Now EIGRP, just to let you know,

01:30:40.520 --> 01:30:46.439
because I know some of you use EIGRP. EIGRP, if I did the same thing, the interfaces don't show up

01:30:46.439 --> 01:30:52.200
here that are passive. So with EIGRP, none of these would show up here if they were passive.

01:30:53.000 --> 01:30:58.839
With OSPF, they still show up here. So with EIGRP, it's a little more trickier in troubleshooting

01:30:58.839 --> 01:31:04.040
the passive interface because they don't show up here at all. Whereas in this case, I know all

01:31:04.040 --> 01:31:07.799
these interfaces are participating in the routing process. And then when I look at this, I can see

01:31:07.799 --> 01:31:13.000
that they're passive. So now I know that all of these are passive and they're participating in the

01:31:13.000 --> 01:31:16.759
routing process. Where the EIGRP is a little more trickier because you got to figure out, okay,

01:31:16.759 --> 01:31:21.399
they are passive, but are they really participating in the routing process? So you'd have to look up

01:31:21.399 --> 01:31:24.919
here to double check and triple check that. So just a little different things to keep in mind

01:31:24.919 --> 01:31:29.319
for EIGRP versus OSPF in the real world, not for the exam. For OSPF for the exam, you're seeing

01:31:29.319 --> 01:31:35.479
what you need to see right now. Okay, what is the other command? Oh, yeah. So if I take a look at

01:31:35.479 --> 01:31:42.520
ShowIPOSPF interface and we look at a very specific interface like VLAN10, what I want

01:31:42.520 --> 01:31:47.479
you to see here is that it actually says no hellos, passive interface as well in this particular output.

01:31:57.560 --> 01:32:04.040
Conrad asked earlier, Conrad, he's there. Okay, you asked any major differences in the ShowIPOSPF

01:32:04.919 --> 01:32:14.439
command when looking at interfaces added using the network command versus the interface command.

01:32:14.439 --> 01:32:20.200
So you'll see here that if you're using the interface command in this output,

01:32:22.680 --> 01:32:27.720
ShowIPOSPF interface, whatever, it'll show you that it's attached via interface

01:32:28.359 --> 01:32:32.279
enable. If you look at it for the network command, so Do Show IP

01:32:33.000 --> 01:32:37.720
OSPF on this router interface, we did the network command on this one,

01:32:38.600 --> 01:32:42.520
you'll see that it says network statement. Is that the answer you were looking for, Conrad?

01:32:44.439 --> 01:32:45.799
Is that what your question was about?

01:32:45.799 --> 01:32:56.200
All right. No, that's about it. So for example, we type in Do Show.

01:32:57.479 --> 01:33:02.919
Show IP protocols will be different. Okay. So Show IP protocols shows it like this instead.

01:33:04.200 --> 01:33:10.520
So Show IP protocols actually shows you your network command. All right. So that's different.

01:33:10.520 --> 01:33:17.720
This is so misleading. I really despise this output. I really do. This output was created,

01:33:17.720 --> 01:33:24.439
this title, Routing for Networks, for RIP version 1. Okay. And so with RIP version 1,

01:33:24.439 --> 01:33:31.479
it was class full addressing and no variable length subnet masking. So that title made sense

01:33:31.479 --> 01:33:38.359
for RIP version 1, but the title doesn't make sense for RIP B2, EIGRP, OSPF, ISIS. It doesn't

01:33:38.359 --> 01:33:42.839
make sense at all, right? Because I am not routing for this network. Does that look like

01:33:42.839 --> 01:33:52.359
a network to you? No. I am routing for the network of the interface that was enabled

01:33:52.359 --> 01:34:00.120
by this network command. That's what it should say. That's what it should say, but it doesn't.

01:34:01.240 --> 01:34:05.399
So that's what it shows up if you use the network command and IP protocols.

01:34:06.040 --> 01:34:11.319
But if you use the interface command in Show IP protocols, it shows up as what? As we saw earlier,

01:34:11.319 --> 01:34:15.560
the actual interface. All right. That's why I am a fan of using the interface level command,

01:34:15.560 --> 01:34:20.680
because this is so much easier to read and view than something like this. This is silly. This is

01:34:20.680 --> 01:34:25.240
nonsense in my opinion. All right. It makes it harder for you to troubleshoot looking at

01:34:25.240 --> 01:34:32.919
something like this than something like this. So yeah. What this really means is that's your

01:34:32.919 --> 01:34:37.080
network command that you use to enable the routing process on that interface.

01:34:39.879 --> 01:34:46.680
Let's take a peek at something like Do Show IP OSPF. I don't really think there's anything

01:34:46.680 --> 01:34:52.120
there, because this is not about the interface. This is purely about the process that is running

01:34:52.120 --> 01:34:55.240
on the device. So here it says there's six interfaces, but it doesn't tell you how they

01:34:55.240 --> 01:35:01.080
were configured. So that's fine there. So Show IP OSPF interface. Yeah. So that's about it.

01:35:01.080 --> 01:35:06.279
That's about it, Conrad. Yeah. For your question. And there's really not anything else that I can

01:35:06.279 --> 01:35:10.040
think about off the top of my head. But if it comes to me as we continue this adventure, I'll

01:35:10.040 --> 01:35:16.600
definitely bring it up and tell you right away when it comes to my head. Yeah. Oh, great questions.

01:35:16.600 --> 01:35:21.240
Great questions. So just to wrap up the oops, wrong thing. Wrap up our passive interface

01:35:21.879 --> 01:35:26.200
discussion here, just so you're aware. Right. I have a little slide. Suppress the sending and

01:35:26.200 --> 01:35:30.279
receiving OSPF message on an interface. Interface is still participating in the OSPF process.

01:35:30.279 --> 01:35:33.959
It's about reducing the amount of OSPF traffic in the layer two network. And ultimately,

01:35:33.959 --> 01:35:39.000
the answer is rogue routers, rogue devices in that layer two network can't form neighbor

01:35:39.000 --> 01:35:42.839
adjacencies with routers and infect our link safety database with false information. So

01:35:42.839 --> 01:35:47.560
think of it security, security, security and performance, both at the exact same time.

01:35:49.959 --> 01:35:54.040
All right. And lastly here, just before we wrap up this discussion, let me just double

01:35:54.040 --> 01:35:58.200
check my slides, my notes. Yeah. This will be our last thing before we take a little breather.

01:35:59.080 --> 01:36:02.919
And then we'll have our config totally done. And then we can start looking at all the other

01:36:02.919 --> 01:36:09.399
things we need to cover for the rest of today's session. So right now, if we analyze our environment,

01:36:09.399 --> 01:36:17.240
we'll see that we can reach every place that is inside our organization. So by doing something

01:36:17.240 --> 01:36:22.359
like show IP route, you'll see that all the networks listed are networks inside of our

01:36:22.359 --> 01:36:28.120
routing domain. So everything that's inside here, everything that's inside here, everything that's

01:36:28.120 --> 01:36:34.439
in the blue area circles, that is what we can reach. Same thing if I go all the way to branch.

01:36:40.120 --> 01:36:47.319
Same idea. Okay. So what are we missing? What are we missing? The ability to get

01:36:47.319 --> 01:36:53.560
everywhere else, the ability to get to every other network we do not know about.

01:36:53.959 --> 01:36:57.799
So for example, right now, if we want to go to the internet, folks, can we go to the internet?

01:36:59.959 --> 01:37:08.040
No. For example, my PC right now, if I try to go to the internet, I can't. Why? Look at DSW-1.

01:37:08.040 --> 01:37:13.640
DSW-1 only knows how to get to everywhere in your own organization. So yeah, we're missing what?

01:37:13.640 --> 01:37:19.799
We're missing the, what type of route is it called? We're missing the, starts with a D,

01:37:20.120 --> 01:37:27.959
starts with a D. Default route. Yeah, absolutely. So right now though, if we go to R2,

01:37:29.240 --> 01:37:34.919
if I type in show IP route, do I have a default route, folks, on R2 right now?

01:37:37.319 --> 01:37:42.279
I do. There it is. 0000 slash zero. So R2 can get to the internet.

01:37:43.000 --> 01:37:50.600
If we type in show run pipe to section IP route, take a peek. There's our default route. I actually

01:37:50.600 --> 01:37:53.560
have a floating static default route configured here as well.

01:38:00.919 --> 01:38:05.560
Now, what are my options? Well, we could go to all of our routers and configure static default

01:38:06.439 --> 01:38:13.799
routes, but that would be silly. What would be a better option here, folks? What would be a better

01:38:13.799 --> 01:38:31.479
option? What if we took this default route and we imported it into OSPF? What if I take that,

01:38:32.279 --> 01:38:42.279
bring it into the link state database? Right now, there is nothing here about a default route. If

01:38:42.279 --> 01:38:48.279
there was, it would show up as a type five, LSA would actually say as a title type five,

01:38:48.279 --> 01:38:55.240
and then you would see 0000. That is the default route in your link state database. It's not here

01:38:55.240 --> 01:39:02.680
anywhere. So how do we do that with OSPF? It's different than EIGRP, that's for sure.

01:39:02.680 --> 01:39:09.479
With OSPF, we have a very special command we can utilize. And what is that very special command?

01:39:09.479 --> 01:39:19.319
It is default dash information originate. Now, when I type that, what that tells the router to do

01:39:19.319 --> 01:39:32.120
is it says, I am having a little bit of issues here. One second, folks. Let me refresh my

01:39:32.680 --> 01:39:36.520
student screen right now. Anybody else having buffering issues?

01:39:39.000 --> 01:39:45.959
No, a little bit of lag, right? Just a little bit. Yeah, okay. So right now, I am having zero

01:39:45.959 --> 01:39:52.040
issues streaming, but it looks like my client is having trouble, right? So if you're not receiving

01:39:52.040 --> 01:39:56.120
any issues, that's fine. But I am not having trouble streaming, I'm just having trouble

01:39:56.120 --> 01:40:01.560
receiving right now. So my stream is fine. Okay. So it's a receiving problem on my end,

01:40:01.560 --> 01:40:06.520
you might not be affected by it. Good. All right. So default information originate

01:40:07.720 --> 01:40:10.520
is the special command. And what does it say? It says,

01:40:11.000 --> 01:40:21.720
look in the routing table for 000 slash zero. It doesn't matter how it got in there.

01:40:22.359 --> 01:40:28.040
It could be in there because of a static default route. It could be in there because you learned

01:40:28.040 --> 01:40:34.040
it via BGP. It could be in there because you learned it via EIGRP. It could be in there,

01:40:34.759 --> 01:40:45.720
it doesn't matter how it got in there. If it is there, no matter how it got there,

01:40:46.839 --> 01:40:55.720
take that and import it into the link state database. That's it. That's what that command

01:40:55.720 --> 01:41:01.240
does. So now we look, it'll always be listed at the bottom, folks, just to let you know.

01:41:01.240 --> 01:41:06.839
And there you go. Type five, we'll talk more about that later. But 000 advertised by me,

01:41:07.479 --> 01:41:19.319
router number two. So now that it's in the link state database, am I going to tell everybody else

01:41:19.319 --> 01:41:25.000
about it? Yep, that's exactly what I'm going to do. And now everybody's going to have an OSPF

01:41:25.959 --> 01:41:33.319
default route. Look at that. Now we can get to the internet because that will cause traffic to

01:41:33.319 --> 01:41:39.720
go from me to R2 out to the internet and back. Likewise, branch would be the same way now.

01:41:40.359 --> 01:41:44.680
Branch would have that in its routing table. And so branch, even though it has an internet

01:41:44.680 --> 01:41:48.200
connection, I don't have a static route set up for that. Why? For the demonstration purposes,

01:41:48.200 --> 01:41:52.600
where we can go from here over to here now and then up because of that route that's in

01:41:52.600 --> 01:41:57.000
the routing table. Now, could we also have this used as an exit point if we want to? Sure,

01:41:57.000 --> 01:42:01.399
of course we could. What about R1? Could we have that too? Sure. Let's go see if R1 has a

01:42:02.120 --> 01:42:07.879
static default route. Look at that. R1 has a static default route, folks. Therefore,

01:42:07.879 --> 01:42:14.200
notice the OSPF route is not in there, is it? Why is the OSPF route not in there

01:42:14.200 --> 01:42:17.879
and the static route in there? What's the magic word? Two words.

01:42:22.600 --> 01:42:28.279
Lower administrative distance. Beautiful. Beautiful. Great answer. Perfect answer.

01:42:29.240 --> 01:42:36.520
So, if I type in show run pipe to section IP route. Let's take that out for a second just to show you.

01:42:41.959 --> 01:42:48.359
I'm removing it. And you'll see the OSPF one's in there now.

01:42:49.319 --> 01:42:55.720
Not bad. Not bad. Perfect example, again, of your what? Administrative distance, how that works.

01:42:58.759 --> 01:43:00.520
All right. So, I just put it back in.

01:43:03.799 --> 01:43:07.799
All right. Now, let's do this. Since we have a static default route here, let's type in router

01:43:07.799 --> 01:43:14.279
OSPF one. Let's do it here as well. Default dash information originate. So, what does that mean now?

01:43:14.680 --> 01:43:18.200
So, what does that mean now? It means I'm also going to inject the default route now.

01:43:21.399 --> 01:43:26.600
So, now we have it twice. Once for me and once from R2. Look at that. Twice.

01:43:29.720 --> 01:43:31.640
So, let's go over to somebody like DSW1.

01:43:38.040 --> 01:43:42.520
I can go two different ways if I wanted to the Internet. Why? Because it's equal cost

01:43:42.520 --> 01:43:50.200
pass to both of those gateways that we have. So, if one fails, the other one can still be used. If

01:43:50.200 --> 01:43:54.759
the other one fails, the other one can still be used. Not bad. Pretty cool. We could even do it

01:43:54.759 --> 01:43:59.479
over on branch if we wanted to as well. And therefore, no matter what, if any of these

01:43:59.479 --> 01:44:03.560
links fail to the Internet, we'd have still the ability to go to the router that still has a

01:44:03.560 --> 01:44:08.279
connection to the Internet. And you can even manipulate this more. I teach you how to manipulate

01:44:08.279 --> 01:44:14.600
this even further in the advanced routing course called an RCENARSI for exam 300-410. I'm just

01:44:14.600 --> 01:44:18.439
looking over there at the numbers I got on my list. Yeah. So, we teach you how to manipulate

01:44:18.439 --> 01:44:22.279
that even more. So, you can control like under normal conditions, I want to go here. If and only

01:44:22.279 --> 01:44:25.399
if that fails, then I want you to fail over to that one for OSPF. If and only if that one fails,

01:44:25.399 --> 01:44:29.080
I want you to fail over that one for OSPF. So, yeah, you can really get creative with these

01:44:29.080 --> 01:44:32.839
right here if you needed to. All right. But that is beyond the scope of Encore. But there you go,

01:44:32.839 --> 01:44:37.640
folks. What did we learn? We've learned how to enable OSPF on all of our routers, enable it on

01:44:37.640 --> 01:44:42.040
all the interfaces, so we can inject the network IDs of all the different interfaces participating

01:44:42.040 --> 01:44:45.000
in OSPF in the link state database, so we can share all that information with everybody.

01:44:45.560 --> 01:44:49.080
And we had fully populated routing tables now. And then what do we do? We looked at passive

01:44:49.080 --> 01:44:55.240
interface. And on top of that, we looked at what else? Default information originate.

01:44:58.680 --> 01:45:03.479
Know all of that if you plan on being successful on the certification exam.

01:45:03.479 --> 01:45:10.359
Config, verify, troubleshoot, very important skills to have for all of that information right there.