WEBVTT 00:00:01.000 --> 00:00:16.000 This next discussion is really, really going to give you the opportunity to understand all the different pieces of the puzzle when it comes to OSPF. 00:00:16.000 --> 00:00:27.000 Remember when we say puzzle, we're talking about puzzle pieces that come together in order for our routers to ultimately learn about everything and figure out the best path through the network. 00:00:27.000 --> 00:00:32.000 What are all these puzzle pieces? Link state advertisements. 00:00:32.000 --> 00:00:45.000 We'll talk about our link state advertisements here and then once we're done, we'll be able to have a better conversation about the metric because we're going to see where the numbers come from and how the numbers are added together to get the results that our router is getting. 00:00:46.000 --> 00:00:54.000 When we look at our routing table, we are going to see that for OSPF, we are going to have some O routes. 00:00:57.000 --> 00:01:00.000 When you look at the top here, it just says simply OSPF. 00:01:01.000 --> 00:01:12.000 O means that that particular network that is listed in the routing table is in the same area as this router. 00:01:13.000 --> 00:01:14.000 That's what that means. 00:01:15.000 --> 00:01:29.000 For example, if we go to R1 right now and I type in show IP route, when we look at this network right here, this network, which is the SVI that lives where? 00:01:29.000 --> 00:01:44.000 On DSW1 and DSW2, that network is in the same area that this router is in and we know R1 is in the same area as DSW1 because we have interfaces in the same area. 00:01:45.000 --> 00:01:48.000 That's how O routes are listed in the routing table. 00:01:48.000 --> 00:01:50.000 Then you have OIA. 00:01:52.000 --> 00:02:00.000 OIA shows up in the routing table like this and up here it just says IA for OSPF inter area. 00:02:01.000 --> 00:02:11.000 Inter area means routes in a different area, but still within the OSPF routing domain. 00:02:12.000 --> 00:02:15.000 If we scroll down just a bit here, you'll see we have two of these. 00:02:15.000 --> 00:02:16.000 Do you remember where these are? 00:02:18.000 --> 00:02:23.000 These are both routes that exist on our branch router. 00:02:24.000 --> 00:02:27.000 Remember, our branch router is in area one. 00:02:28.000 --> 00:02:33.000 These are networks that are in a totally different area than this router is in. 00:02:38.000 --> 00:02:44.000 Then our last one that we have on this list up here in our slides are E1s and E2s. 00:02:45.000 --> 00:02:47.000 You'll see down here we have an E2. 00:02:47.000 --> 00:02:48.000 What is that? 00:02:48.000 --> 00:02:49.000 That's the default route. 00:02:51.000 --> 00:03:00.000 E1s and E2s are routes to destinations outside the OSPF routing domain. 00:03:01.000 --> 00:03:07.000 The default route would be an E1, E2 route if you were doing redistribution. 00:03:08.000 --> 00:03:18.000 Meaning, for example, importing routes from EIGRP into OSPF or importing routes from BGP into OSPF 00:03:18.000 --> 00:03:25.000 or importing routes from RIP into OSPF or redistributing static routes into OSPF. 00:03:26.000 --> 00:03:34.000 Anytime you use the redistribute command and you import routes from a totally different source, 00:03:34.000 --> 00:03:38.000 that's how you get E1s and E2s. 00:03:40.000 --> 00:03:42.000 The E2 is the default. 00:03:42.000 --> 00:03:44.000 If you don't change it, it stays as E2. 00:03:45.000 --> 00:03:48.000 If you change it, you can change it to E1. 00:03:49.000 --> 00:03:52.000 That would just simply change how the metric is calculated. 00:03:52.000 --> 00:03:56.000 The difference between E2 and E1 is how the metric is calculated. 00:03:56.000 --> 00:03:57.000 That is it. 00:03:57.000 --> 00:03:59.000 We're not going to get into that discussion right now. 00:04:00.000 --> 00:04:02.000 For example, you see E2. 00:04:02.000 --> 00:04:03.000 We have a value of 1 there. 00:04:03.000 --> 00:04:08.000 If I change it to an E1 when it was being imported, it would just be calculated in a different way. 00:04:09.000 --> 00:04:10.000 We'll learn. 00:04:10.000 --> 00:04:11.000 Do we learn that? 00:04:11.000 --> 00:04:12.000 No. 00:04:12.000 --> 00:04:13.000 That's an advanced routing one. 00:04:13.000 --> 00:04:18.000 That would be for more complex routing environments when you have multiple exit points out of your routing domain 00:04:18.000 --> 00:04:21.000 and you wanted to control which exit point would be utilized. 00:04:21.000 --> 00:04:24.000 You can manipulate the values that you see here in many different ways. 00:04:24.000 --> 00:04:31.000 One of the things I like to point out, though, to people here is that in the end, E1 or E2 is a choice. 00:04:31.000 --> 00:04:33.000 E2 is a choice you make. 00:04:33.000 --> 00:04:40.000 It's a choice you make based simply on how you want your router to decide the best way to go through the environment. 00:04:40.000 --> 00:04:47.000 When you learn about the manipulation factors of E2 in an RC and you learn about the manipulation factors of E1 in an RC, 00:04:47.000 --> 00:04:53.000 then what that does is it gives you flexibility to control the decision-making process of your router. 00:04:53.000 --> 00:04:56.000 That's all you really get out of that when it's all said and done. 00:04:57.000 --> 00:04:58.000 All right. 00:04:58.000 --> 00:05:03.000 So, we know now that we have three different types of routes. 00:05:03.000 --> 00:05:07.000 Now, there is another option, N1 and N2s. 00:05:08.000 --> 00:05:13.000 We are not going to be getting into N1s and N2s in this course. 00:05:13.000 --> 00:05:15.000 When do we see N1s and N2s? 00:05:15.000 --> 00:05:25.000 We see it when we build a network, build OSPF routing domain with what are called not-so-stubby areas and totally not-so-stubby areas. 00:05:26.000 --> 00:05:33.000 When we have those types of areas, OSPF behaves differently for those areas. 00:05:33.000 --> 00:05:40.000 And as a result of that, it will create what are called N1 routes and N2 routes for specific scenarios and circumstances. 00:05:40.000 --> 00:05:47.000 But N1 and N2 routes will only be visible inside the not-so-stubby area and the totally not-so-stubby area. 00:05:47.000 --> 00:05:50.000 They won't be visible outside of those areas. 00:05:50.000 --> 00:05:53.000 Outside of those areas, they get converted to type 5s. 00:05:53.000 --> 00:05:55.000 They get converted to E1s and E2s. 00:05:55.000 --> 00:06:03.000 So, for example, if you had a not-so-stubby area with an N1 in it, everywhere else in the organization would show up as an E1 route. 00:06:03.000 --> 00:06:11.000 If you had E2 routes, sorry, N2 routes in the not-so-stubby area, then everywhere else, everyone else would see them as what? 00:06:11.000 --> 00:06:13.000 As E2 routes instead. 00:06:13.000 --> 00:06:14.000 So, that's more than you need to know for the exam. 00:06:14.000 --> 00:06:15.000 You won't even be tested on that stuff. 00:06:15.000 --> 00:06:20.000 I just want to let you know that, yes, there's another option, and you'll learn about that in the advanced routing course. 00:06:21.000 --> 00:06:24.000 So, LSAs, link state advertisements. 00:06:24.000 --> 00:06:28.000 Link state advertisements are, think about it like a Post-it note. 00:06:28.000 --> 00:06:31.000 You can think about link state advertisement as a Post-it note. 00:06:31.000 --> 00:06:39.000 And if I wanted to send that information to you, I could take that Post-it note, and I can put it in an envelope, the OSPF packet, the link state update, right? 00:06:39.000 --> 00:06:41.000 The link state update is the envelope. 00:06:41.000 --> 00:06:42.000 That's the packet. 00:06:42.000 --> 00:06:49.000 And I can put LSAs inside of it, a note, a Post-it note, anything I want to put to teach you something when it's all said and done. 00:06:49.000 --> 00:06:58.000 So, remember, we take these LSAs, and we use them to exchange the information and the details between all of our different routers. 00:06:58.000 --> 00:07:01.000 And we're going to exchange LSAs as soon as neighborhoods are formed. 00:07:01.000 --> 00:07:10.000 We're going to exchange LSAs whenever a change occurs, and then we'll also exchange LSAs on a regular basis, and that is every 30 minutes by default. 00:07:11.000 --> 00:07:22.000 So, that is why when you look at your OSPF database, you see that there is an aging timer for every single one of your LSAs. 00:07:22.000 --> 00:07:26.000 Your LSA's maximum age is one hour. 00:07:26.000 --> 00:07:28.000 So, what is that, 3,600 seconds, right? 00:07:28.000 --> 00:07:30.000 Is that right, 3,600 seconds? 00:07:30.000 --> 00:07:32.000 So, that's your maximum age. 00:07:32.000 --> 00:07:36.000 So, right now, you can already see some of them are already at 30 minutes, 30 seconds. 00:07:36.000 --> 00:07:38.000 Yeah, 30 minutes. 00:07:38.000 --> 00:07:41.000 So, you got one hour, all right? 00:07:41.000 --> 00:07:53.000 But we will typically update our LSA every 30 minutes, every 30 minutes. 00:07:56.000 --> 00:08:06.000 So, some of those ones that you saw at 1,900 seconds are probably going to be updated here pretty soon. 00:08:08.000 --> 00:08:11.000 And refresh and start back at a timer of zero. 00:08:13.000 --> 00:08:16.000 Trying to see if I can get that to happen right now in the back. 00:08:16.000 --> 00:08:18.000 Nope, not yet. 00:08:18.000 --> 00:08:19.000 All right, we'll just keep an eye on that. 00:08:19.000 --> 00:08:21.000 So, we got some of them at 19 right now. 00:08:21.000 --> 00:08:24.000 I'll keep an eye on that, see if they flip over, and then I'll show you. 00:08:25.000 --> 00:08:32.000 So, we have Type 1, we have Type 2, we have Type 3, we have Type 4, we have Type 5. 00:08:33.000 --> 00:08:38.000 Notice the Type 1 is really what primarily gives you those O routes. 00:08:39.000 --> 00:08:43.000 Notice that a Type 3 is what really gives you those OIA routes. 00:08:43.000 --> 00:08:48.000 Notice the Type 5 is really what gives you the E routes, E1s and E2s. 00:08:48.000 --> 00:08:55.000 And then Type 7, which is not on this list because you don't need to know it for this course or exam, is what gives you those N1 and N2 routes. 00:08:56.000 --> 00:09:04.000 So, 1 for O, 3 for OIA, 5 for E, and 7 for the N routes, which you don't need to know about. 00:09:07.000 --> 00:09:11.000 What you do need to understand is the scope of these different LSA types. 00:09:14.000 --> 00:09:21.000 So, notice here that I have Type 1 and Type 2s that are scoped only to their area. 00:09:22.000 --> 00:09:26.000 Meaning, they will never, ever, ever, ever cross an area boundary. 00:09:26.000 --> 00:09:28.000 They are stuck in that area. 00:09:28.000 --> 00:09:32.000 So, when you think about Type 1s and Type 2s, they will only bounce around in here. 00:09:32.000 --> 00:09:34.000 They will only bounce around in here, that's it. 00:09:34.000 --> 00:09:37.000 They will only bounce around, 1 and 2, that's the best way to think about it. 00:09:38.000 --> 00:09:42.000 Type 3s are going to be generated by this router, generated by this router and jumped in. 00:09:42.000 --> 00:09:44.000 Generated by the router and jumped in. 00:09:45.000 --> 00:09:48.000 So, the area border router generates Type 3s. 00:09:48.000 --> 00:09:52.000 And then once a Type 3 is sent in here, it only floats around in that area. 00:09:53.000 --> 00:09:56.000 When I generate a Type 3 and send it, it only floats around in that area. 00:09:57.000 --> 00:09:58.000 And what about Type 4s? 00:09:58.000 --> 00:10:03.000 Notice that Type 4, again, generated by the ABR, but it's a very special option. 00:10:04.000 --> 00:10:09.000 And it will be generated by the ABR and just dumped into that area for that area, that's it. 00:10:10.000 --> 00:10:11.000 And then look at the Type 5. 00:10:11.000 --> 00:10:14.000 The Type 5 is generated by an ASBR. 00:10:14.000 --> 00:10:22.000 And it's going to be dumped into this area for this area and then it gets forwarded without modification into every other area. 00:10:24.000 --> 00:10:26.000 So, let's get into these in a little more detail. 00:10:26.000 --> 00:10:28.000 That was just a quick overview. 00:10:29.000 --> 00:10:31.000 So, let's look at our routing domain right now. 00:10:33.000 --> 00:10:37.000 So, we have Type 1s and Type 2s that are going to be floating around in here. 00:10:38.000 --> 00:10:42.000 We have Type 1s and Type 2s that are going to be floating around in here. 00:10:42.000 --> 00:10:45.000 We have Type 1s and Type 2s that are going to be floating around here. 00:10:47.000 --> 00:10:53.000 These Type 1s and Type 2s are Area 1 Type 1s and Type 2s. 00:10:55.000 --> 00:10:57.000 Area 1 Type 1s and Type 2s. 00:10:58.000 --> 00:11:01.000 These are Area 0 Type 1 and Type 2s. 00:11:02.000 --> 00:11:03.000 And they will never cross. 00:11:04.000 --> 00:11:05.000 This is your scope. 00:11:05.000 --> 00:11:06.000 This is your boundary line. 00:11:06.000 --> 00:11:09.000 You will never cross over an area border router. 00:11:10.000 --> 00:11:18.000 These two, Type 1 and Type 2, are the most fundamental puzzle pieces for OSPF. 00:11:18.000 --> 00:11:29.000 It is the Type 1s and Type 2s that build the topological map, that build the environment that the router is seeing. 00:11:30.000 --> 00:11:38.000 So, what will happen here is R1 through Type 1s and Type 2s know this router exists, knows this router exists, knows this router exists, 00:11:38.000 --> 00:11:47.000 and knows every single interface and network in Area 0 and can actually, from that link state database, 00:11:47.000 --> 00:11:58.000 so if we go to DSW-1 as an example here, that link state database, it can actually build the topological map with Type 1s 00:11:58.000 --> 00:12:02.000 and it can build the topological map with the Type 2s combining them together. 00:12:02.000 --> 00:12:05.000 So, router link states, Type 1. 00:12:05.000 --> 00:12:08.000 Network link states, Type 2. 00:12:08.000 --> 00:12:14.000 You combine those together, you get your map of your area. 00:12:14.000 --> 00:12:17.000 So, again, when I say map, do I really mean map? 00:12:17.000 --> 00:12:18.000 I really mean map. 00:12:19.000 --> 00:12:24.000 Each router is on the map with all the lines drawn between them. 00:12:25.000 --> 00:12:27.000 Now, do you actually get to tell your router to show you that map? 00:12:27.000 --> 00:12:29.000 No, you don't, unfortunately. 00:12:29.000 --> 00:12:37.000 But does that mean that you could actually open up every single one of these LSAs, these Type 1s and Type 2s, 00:12:37.000 --> 00:12:42.000 and you actually draw a diagram from that information? 00:12:42.000 --> 00:12:43.000 Yes, you can. 00:12:44.000 --> 00:12:45.000 Yes, you can. 00:12:48.000 --> 00:12:53.000 And the cool thing is, is it doesn't matter which router you go to in the area. 00:12:53.000 --> 00:13:01.000 Whether I go to DSW1 or I go to DSW2 or I go to R1 or I go to R2 for Area 0, 00:13:01.000 --> 00:13:05.000 when I take that information, remember, they're all synchronized. 00:13:05.000 --> 00:13:12.000 It doesn't matter which one I use, I will get the same map for all of those routers in Area 0. 00:13:12.000 --> 00:13:18.000 And then if I did the same thing for Area 1, I would get the same map for Area 1. 00:13:18.000 --> 00:13:22.000 It doesn't matter which router I use in Area 1, I'd get the same result for all of them. 00:13:23.000 --> 00:13:24.000 Why? 00:13:24.000 --> 00:13:25.000 Synchronization. 00:13:25.000 --> 00:13:26.000 Remember that. 00:13:29.000 --> 00:13:32.000 So what exactly is the Type 1 LSA? 00:13:32.000 --> 00:13:41.000 So the Type 1 LSA is an LSA that every single router generates. 00:13:41.000 --> 00:13:45.000 And we saw that in our environment. 00:13:45.000 --> 00:13:46.000 Router 1 generated it. 00:13:46.000 --> 00:13:47.000 Router 2 generated it. 00:13:47.000 --> 00:13:48.000 Router 3 generated it. 00:13:48.000 --> 00:13:49.000 Router 4 generated it. 00:13:49.000 --> 00:13:51.000 You might be saying, hey, Raymond, where's Router 5? 00:13:51.000 --> 00:13:53.000 Remember, this is Area 0. 00:13:53.000 --> 00:13:58.000 Router 5 does not live in Area 0. 00:13:58.000 --> 00:14:00.000 That's why it's not in this list. 00:14:00.000 --> 00:14:02.000 I'm on DSW1. 00:14:02.000 --> 00:14:05.000 This is Area 0, not Area 1. 00:14:05.000 --> 00:14:06.000 This is all we know. 00:14:06.000 --> 00:14:08.000 So I know about these four routers. 00:14:08.000 --> 00:14:10.000 And no, it's not external. 00:14:10.000 --> 00:14:12.000 It is just outside. 00:14:12.000 --> 00:14:14.000 It is in a different area, not external. 00:14:14.000 --> 00:14:16.000 External to the area, yes. 00:14:16.000 --> 00:14:20.000 But when we use the term external in OSPF, external means outside of OSPF. 00:14:20.000 --> 00:14:21.000 That's not outside of OSPF. 00:14:21.000 --> 00:14:22.000 Right? 00:14:22.000 --> 00:14:23.000 It's just outside the area. 00:14:23.000 --> 00:14:24.000 Yeah. 00:14:24.000 --> 00:14:28.000 It's not external, just outside of the area. 00:14:28.000 --> 00:14:33.000 So in this case, all the Type 1s are for what purpose? 00:14:33.000 --> 00:14:40.000 Every router generates a Type 1 for the area and says, yoo-hoo, over here. 00:14:40.000 --> 00:14:41.000 Yeah, look at me. 00:14:41.000 --> 00:14:42.000 Look at me. 00:14:42.000 --> 00:14:45.000 I am 0.0.0.1. 00:14:45.000 --> 00:14:50.000 And I have three links participating in the routing process. 00:14:50.000 --> 00:14:57.000 And my links are this. 00:14:57.000 --> 00:15:00.000 There's my information. 00:15:00.000 --> 00:15:05.000 So when every single router does this, 00:15:05.000 --> 00:15:09.000 and they share it with each other in the area through the LSA flooding 00:15:09.000 --> 00:15:13.000 process, then you learn directly from that router. 00:15:13.000 --> 00:15:16.000 You get a copy of its LSA, Type 1 LSA. 00:15:16.000 --> 00:15:18.000 This is me. 00:15:18.000 --> 00:15:21.000 These are the networks I'm connected to. 00:15:21.000 --> 00:15:28.000 This is the metric of that interface that's connected to that network. 00:15:28.000 --> 00:15:30.000 Yeah. 00:15:30.000 --> 00:15:32.000 Basically, it's all about me. 00:15:32.000 --> 00:15:33.000 Exactly. 00:15:33.000 --> 00:15:35.000 It's all about you. 00:15:35.000 --> 00:15:38.000 That's the Type 1 LSA. 00:15:39.000 --> 00:15:44.000 So it's about you describing who you are to the other routers in the area 00:15:44.000 --> 00:15:48.000 and all your interfaces that are participating in the routing process. 00:15:48.000 --> 00:15:51.000 So in the end, you all know about each other. 00:15:51.000 --> 00:15:58.000 And that's why in yesterday's session when we looked at our design image, 00:15:58.000 --> 00:16:00.000 it was this one right here. 00:16:00.000 --> 00:16:05.000 And we were talking about the fact that if you are single area, 00:16:06.000 --> 00:16:10.000 the Type 1 is very, very detrimental to you. 00:16:10.000 --> 00:16:14.000 Because if you're a giant single area, every time a change happens, 00:16:14.000 --> 00:16:16.000 you have to go, look at me. 00:16:16.000 --> 00:16:20.000 Yeah, look, this network has changed. 00:16:20.000 --> 00:16:25.000 And what happens when another router receives your Type 1 LSA? 00:16:25.000 --> 00:16:30.000 They have to rebuild that entire topological map. 00:16:30.000 --> 00:16:33.000 They have to go through the entire process of saying, okay, this is me. 00:16:33.000 --> 00:16:34.000 That's you. 00:16:34.000 --> 00:16:35.000 That's so-and-so. 00:16:35.000 --> 00:16:36.000 That's so-and-so. 00:16:36.000 --> 00:16:37.000 You have all these networks. 00:16:37.000 --> 00:16:39.000 They have all these networks. 00:16:39.000 --> 00:16:40.000 Build all the lines. 00:16:40.000 --> 00:16:41.000 Build all the maps. 00:16:41.000 --> 00:16:45.000 Run Dijkstra's shortest path first calculation algorithm against all of that 00:16:45.000 --> 00:16:47.000 to ultimately figure out what? 00:16:47.000 --> 00:16:53.000 Pretty much the same thing you had before, but one network's missing 00:16:53.000 --> 00:16:55.000 or one network's been added. 00:16:55.000 --> 00:17:01.000 So, yes, that is a flaw in the design of the Type 1 LSA. 00:17:01.000 --> 00:17:03.000 And it has been recognized as that. 00:17:03.000 --> 00:17:07.000 So that way there with OSPF v3, OSPF v3, 00:17:07.000 --> 00:17:09.000 they actually changed the behavior of the Type 1 LSA. 00:17:09.000 --> 00:17:11.000 That's right, they did. 00:17:11.000 --> 00:17:16.000 And they added more LSA types for OSPF v3 to solve that problem. 00:17:16.000 --> 00:17:23.000 So it's not as detrimental now when a network gets added or removed. 00:17:23.000 --> 00:17:26.000 As long as nothing's happened to the router, 00:17:26.000 --> 00:17:32.000 we don't have to recalculate everything with OSPF v3 address families 00:17:32.000 --> 00:17:34.000 or OSPF v3 for IPv6. 00:17:34.000 --> 00:17:40.000 It's a flaw in IPv4 LSAs that they remove the flaw from IPv6 LSAs 00:17:40.000 --> 00:17:42.000 and OSPF address families, which is great. 00:17:42.000 --> 00:17:46.000 That's why I always convince people, hey, if you can use address families nowadays 00:17:46.000 --> 00:17:50.000 because with the address families you don't have this issue anymore. 00:17:50.000 --> 00:17:54.000 So you could have larger OSPF routing domains if you're using address families 00:17:54.000 --> 00:17:58.000 because you're not going to have to worry about if a network gets added or removed. 00:17:58.000 --> 00:18:02.000 There's a new type of LSA called the Type 9 LSA that takes care of that. 00:18:02.000 --> 00:18:05.000 That's not here for OSPF v2. 00:18:05.000 --> 00:18:07.000 And that way we don't have to recalculate the map 00:18:07.000 --> 00:18:10.000 and do Dijkstra's algorithm anymore, which is great. 00:18:10.000 --> 00:18:14.000 Because once a map is built, you can add or remove networks. 00:18:14.000 --> 00:18:16.000 You don't have to recalculate the map, right? 00:18:16.000 --> 00:18:18.000 I mean, you already got the map. 00:18:18.000 --> 00:18:22.000 So anyways, as you can see, it's just not efficient, 00:18:22.000 --> 00:18:26.000 the existence or the Type 1 LSA for OSPF v2. 00:18:26.000 --> 00:18:30.000 So they didn't modify it for other versions of OSPF going forward. 00:18:30.000 --> 00:18:34.000 So Type 1 LSA, most fundamental, though, no matter what, right? 00:18:34.000 --> 00:18:38.000 In all regards, it's the one that builds the topological map. 00:18:38.000 --> 00:18:40.000 Generated by every router. 00:18:40.000 --> 00:18:42.000 Flooded to everyone in the area. 00:18:42.000 --> 00:18:44.000 Those are the things you want to remember. 00:18:44.000 --> 00:18:47.000 They also generate the what? The O routes. 00:18:47.000 --> 00:18:50.000 So every single O route. 00:18:50.000 --> 00:18:57.000 So when we look at our every O route you see in here, 00:18:57.000 --> 00:18:59.000 that does not have any other code. 00:18:59.000 --> 00:19:02.000 So this one and this one as an example, 00:19:02.000 --> 00:19:07.000 both of those would have been strictly 100% from the Type 1 LSA. 00:19:07.000 --> 00:19:09.000 That's where they would have came from. 00:19:09.000 --> 00:19:11.000 So go to R1 as an example. 00:19:11.000 --> 00:19:16.000 All of these are from the Type 1 LSAs. 00:19:16.000 --> 00:19:21.000 We'll leave that for the exam. 00:19:21.000 --> 00:19:23.000 Okay, what about the Type 2s, though? 00:19:23.000 --> 00:19:27.000 What in the world are the Type 2s all about? 00:19:27.000 --> 00:19:31.000 So when you look at Type 2s, those are called the network link states. 00:19:31.000 --> 00:19:37.000 So, again, the scope of the Type 2 is only within the area. 00:19:37.000 --> 00:19:39.000 But who generates Type 2s? 00:19:39.000 --> 00:19:45.000 Well, we said Type 1s were all routers. 00:19:45.000 --> 00:19:48.000 Who generates the Type 2s? 00:19:48.000 --> 00:19:50.000 Designated routers. 00:19:50.000 --> 00:19:52.000 That's it. 00:19:52.000 --> 00:19:59.000 So the designated router for a multi-axis network in that area 00:19:59.000 --> 00:20:03.000 advertises a Type 2 LSA. 00:20:03.000 --> 00:20:06.000 Why does it have to do that? 00:20:06.000 --> 00:20:13.000 It does that to describe every single router that is attached 00:20:13.000 --> 00:20:19.000 to that multi-axis network, to all the other routers in the area. 00:20:19.000 --> 00:20:22.000 And the reason why is because when you have a designated router, 00:20:22.000 --> 00:20:26.000 you actually have blind spots in your topology. 00:20:26.000 --> 00:20:28.000 You have blind spots. 00:20:28.000 --> 00:20:30.000 That's what you have. 00:20:30.000 --> 00:20:33.000 Because, for example, let's say we had a router here, 00:20:33.000 --> 00:20:36.000 and we had a router here, and then we had a switch here, 00:20:36.000 --> 00:20:39.000 and we had a router, router, router, router. 00:20:39.000 --> 00:20:42.000 I'm not going to keep putting R's on them. 00:20:42.000 --> 00:20:44.000 And a router here, and a router here, and a router here, 00:20:44.000 --> 00:20:47.000 and a router here. 00:20:47.000 --> 00:20:51.000 So in this environment here, without a doubt, no matter what, 00:20:51.000 --> 00:20:53.000 we're going to have to have a designated router. 00:20:53.000 --> 00:20:56.000 Let's say it's this router here. 00:20:56.000 --> 00:21:02.000 The thing is, with Type 1 LSAs, with just purely Type 1 LSAs, 00:21:02.000 --> 00:21:05.000 all of the routers in this environment, all routers in this area, 00:21:05.000 --> 00:21:10.000 so this is one big area, okay, area, let's say 51. 00:21:10.000 --> 00:21:13.000 All the routers are in area 51. 00:21:13.000 --> 00:21:16.000 So with all of these routers in area 51, 00:21:16.000 --> 00:21:19.000 they will learn about all the routers, 00:21:19.000 --> 00:21:24.000 but because of this environment being broadcast, 00:21:24.000 --> 00:21:29.000 or B-R-O-A, broadcast, or what else do we call it, 00:21:29.000 --> 00:21:35.000 M-U, multi-access, because it's multi-access, 00:21:35.000 --> 00:21:41.000 the Type 1 LSAs alone do not allow the routers to understand 00:21:41.000 --> 00:21:45.000 what's actually going on in that environment 00:21:45.000 --> 00:21:48.000 and how everyone is connected to everyone else. 00:21:48.000 --> 00:21:52.000 There's just not enough information in the Type 1. 00:21:52.000 --> 00:21:57.000 So the designated router generates a Type 2, 00:21:57.000 --> 00:22:00.000 floods it to everyone in that area, 00:22:00.000 --> 00:22:04.000 so in this case, floods it to everyone in that area, 00:22:04.000 --> 00:22:07.000 and the end result is that the designated router is essentially 00:22:07.000 --> 00:22:09.000 telling all the other routers, 00:22:09.000 --> 00:22:12.000 I'm the designated router for this multi-access network, 00:22:12.000 --> 00:22:15.000 and this device, this device, this device, this device, 00:22:15.000 --> 00:22:18.000 and me are all connected to it. 00:22:18.000 --> 00:22:20.000 So based on that information now, 00:22:20.000 --> 00:22:23.000 they can finish building their topology. 00:22:23.000 --> 00:22:28.000 So if we look at, for example, the database for the network LSAs, 00:22:28.000 --> 00:22:32.000 let's take a peek at this network LSA right here. 00:22:37.000 --> 00:22:41.000 And you'll see here that it says for this multi-access network, 00:22:41.000 --> 00:22:46.000 these two routers are connected to it, and it's a Slash 30 network. 00:22:46.000 --> 00:22:47.000 That's it. 00:22:47.000 --> 00:22:49.000 It's very simple. 00:22:49.000 --> 00:22:52.000 It's just the designated router saying, hey, 00:22:52.000 --> 00:22:54.000 I've got a multi-access network here, 00:22:54.000 --> 00:22:57.000 these are the routers connected to it, and it's a Slash 30 network. 00:22:58.000 --> 00:23:01.000 Now take your Type 1 LSAs you've learned from everyone 00:23:01.000 --> 00:23:03.000 and take the information that I've just given you 00:23:03.000 --> 00:23:06.000 and figure out your topology. 00:23:06.000 --> 00:23:08.000 That's what it's doing. 00:23:08.000 --> 00:23:12.000 So in the end, now every router understands what's going on here 00:23:12.000 --> 00:23:16.000 based on a combination of the Type 1s and the Type 2 LSAs. 00:23:18.000 --> 00:23:23.000 So based on these two LSAs now, Type 1s and Type 2s, 00:23:23.000 --> 00:23:30.000 we have all the puzzle pieces we need to build the area topological map 00:23:30.000 --> 00:23:33.000 and then use Dijkstra's Shortest Path First algorithm 00:23:33.000 --> 00:23:40.000 to figure out the quickest way to get to every position in the area, 00:23:40.000 --> 00:23:42.000 just our area. 00:23:42.000 --> 00:23:45.000 So Dijkstra's Shortest Path First algorithm and the map 00:23:45.000 --> 00:23:50.000 are used to figure out the best way to get to every place in our area. 00:23:50.000 --> 00:23:52.000 So this would happen in Area 0. 00:23:52.000 --> 00:23:54.000 This would happen in Area 1. 00:23:54.000 --> 00:23:56.000 This would happen in Area 51. 00:23:56.000 --> 00:24:02.000 And that information is purely, purely, purely contained to just that area. 00:24:06.000 --> 00:24:09.000 So now that raises the question, 00:24:09.000 --> 00:24:14.000 how does the information in Area 0 get to Area 1? 00:24:14.000 --> 00:24:19.000 How does the information in Area 1 get to Area 0? 00:24:19.000 --> 00:24:24.000 That is where the Type 3 LSA comes into play. 00:24:24.000 --> 00:24:28.000 The Type 3 LSA is generated by who? 00:24:28.000 --> 00:24:33.000 The area border router. 00:24:37.000 --> 00:24:42.000 In our case, R2, who is connected to Area 0 00:24:42.000 --> 00:24:47.000 and connected to some other area, in this case, Area 1. 00:24:47.000 --> 00:24:50.000 When the area border router generates a Type 3 LSA, 00:24:50.000 --> 00:24:51.000 what is it actually doing? 00:24:51.000 --> 00:24:53.000 Now, notice it says Summary LSA. 00:24:53.000 --> 00:25:00.000 That is probably the worst wording they could have used to describe it 00:25:00.000 --> 00:25:03.000 because what that leads most people to believe 00:25:03.000 --> 00:25:06.000 is we're talking about summarization. 00:25:06.000 --> 00:25:11.000 That's not what we're talking about, not even close to it. 00:25:11.000 --> 00:25:16.000 Summarization is a totally different thing that we will discuss a little later. 00:25:21.000 --> 00:25:26.000 But here we have this Summary LSA. 00:25:26.000 --> 00:25:28.000 What does it mean? 00:25:28.000 --> 00:25:34.000 It means I'm going to take the Type 1 information from this area 00:25:34.000 --> 00:25:42.000 and I'm going to condense it down to just give you what you need to know. 00:25:42.000 --> 00:25:46.000 I'm going to take the information, the Type 1 information from here 00:25:46.000 --> 00:25:49.000 and condense it down and send it into here. 00:25:49.000 --> 00:25:56.000 When we say condense it down, let's examine what that actually means. 00:25:56.000 --> 00:26:00.000 We know right now, if we go to R2 as an example, 00:26:00.000 --> 00:26:02.000 we are part of two different areas. 00:26:02.000 --> 00:26:06.000 I told you a while ago, show IP OSPF database, 00:26:06.000 --> 00:26:10.000 that I am going to have two different databases on R2. 00:26:10.000 --> 00:26:15.000 I'm going to have an Area 0 database and I'm going to have an Area 1 database. 00:26:20.000 --> 00:26:22.000 I have a database for each of these. 00:26:22.000 --> 00:26:27.000 Now, if we think about Area 1, Type 1 LSAs, 00:26:27.000 --> 00:26:31.000 there's a lot of details in each and every single one of these. 00:26:31.000 --> 00:26:36.000 If we open up any one of these, there's a lot of details in there. 00:26:36.000 --> 00:26:44.000 What we want to do is we simply want to take the network ID and the metric, 00:26:44.000 --> 00:26:48.000 sorry, the network ID, that's it, 00:26:48.000 --> 00:26:52.000 and teach everybody else about it, just the network ID. 00:26:52.000 --> 00:26:55.000 But what I'll also do is include my metric 00:26:55.000 --> 00:26:58.000 in order to get to that particular network. 00:26:58.000 --> 00:27:02.000 Based on the Type 1 and Type 2 LSAs here, 00:27:02.000 --> 00:27:07.000 R2 knows how to get to, let's say, 10.0.0.0. 00:27:07.000 --> 00:27:09.000 Who owns that? 0.0.0.3. 00:27:09.000 --> 00:27:11.000 Let's just take a look at that one, for example. 00:27:11.000 --> 00:27:16.000 We'll go router, 0.0.0.3, that's DSW1. 00:27:16.000 --> 00:27:18.000 What network is that? Let's find it here. 00:27:18.000 --> 00:27:20.000 It's this one right here. 00:27:20.000 --> 00:27:23.000 I have learned it as a Type 1 LSA. 00:27:23.000 --> 00:27:26.000 DSW1 says my metric for that interface is 1. 00:27:26.000 --> 00:27:29.000 Okay, well, R2, using Type 1 and Type 2, 00:27:29.000 --> 00:27:32.000 builds its map, and it ultimately figures out in the end 00:27:32.000 --> 00:27:36.000 how far that network actually is away from it. 00:27:36.000 --> 00:27:39.000 How far are you actually away from me? 00:27:39.000 --> 00:27:44.000 So your cost plus my cost to get to you. 00:27:44.000 --> 00:27:47.000 Then what's going to happen here is the Area Border Router 00:27:47.000 --> 00:27:54.000 takes this network ID, builds a Type 3 LSA from that, 00:27:54.000 --> 00:27:56.000 sends it into Area 1, and says, 00:27:56.000 --> 00:28:01.000 hey, if you want to get to 10.0.0.0.24, 00:28:01.000 --> 00:28:07.000 send your traffic to me, R2, and I will take care of it for you. 00:28:07.000 --> 00:28:12.000 Oh, and by the way, my metric to that network is, let's say, 3. 00:28:12.000 --> 00:28:17.000 So use my number of 3 plus whatever you need to calculate 00:28:17.000 --> 00:28:20.000 to get to me, and that's going to be your metric. 00:28:21.000 --> 00:28:25.000 So when we look at the Type 3 LSA now here on R2, 00:28:25.000 --> 00:28:29.000 let's go show IPOSPF database again, 00:28:29.000 --> 00:28:32.000 is that going to be an Area 0 Type 3? 00:28:32.000 --> 00:28:33.000 No, no, no, no, right? 00:28:33.000 --> 00:28:35.000 That's going to be an Area 1 Type 3 now. 00:28:35.000 --> 00:28:40.000 So look, if we go to the Area 1 Type 3s, there it is. 00:28:40.000 --> 00:28:43.000 It actually shows up as 10.0.0.0. 00:28:43.000 --> 00:28:47.000 Look at the other one, 10.0.1.0, 10.0.2.0, 10. 00:28:47.000 --> 00:28:49.000 So I'm only advertising the network ID. 00:28:49.000 --> 00:28:50.000 It's me. 00:28:50.000 --> 00:28:53.000 Me, I'm advertising that. 00:28:53.000 --> 00:29:01.000 So if I type in here summary 10.0.0.0, this is what I'm telling Area 1. 00:29:01.000 --> 00:29:07.000 I am saying, hey, I know about this network called 10.0.0.0.24, 00:29:07.000 --> 00:29:10.000 and I'm telling you about it. 00:29:10.000 --> 00:29:11.000 But it's over there somewhere. 00:29:11.000 --> 00:29:14.000 You don't have to worry about the details because the details don't matter 00:29:14.000 --> 00:29:18.000 because no matter what, you have to come through me. 00:29:18.000 --> 00:29:20.000 You have to come through me. 00:29:20.000 --> 00:29:25.000 So everybody in Area 1 learns from the Area Border Router about 10.0.0.1 00:29:25.000 --> 00:29:28.000 or anything in Area 0. 00:29:28.000 --> 00:29:29.000 So you don't know the details. 00:29:29.000 --> 00:29:31.000 You don't even know who owns it, right? 00:29:31.000 --> 00:29:33.000 You are learning from the Area Border Router. 00:29:33.000 --> 00:29:36.000 You don't even know DSW-1 exists. 00:29:36.000 --> 00:29:40.000 You'll never know that either if you're in Area 1. 00:29:40.000 --> 00:29:44.000 That's how that information from other areas is exchanged. 00:29:44.000 --> 00:29:46.000 So another example for you is what? 00:29:46.000 --> 00:29:51.000 Well, if we take a peek at, for example, Area 1. 00:29:51.000 --> 00:30:01.000 If we look at Area 1 on R2, we have router number 5, 00:30:01.000 --> 00:30:03.000 the branch router over here. 00:30:03.000 --> 00:30:07.000 The branch router has five links participating in the routing process. 00:30:07.000 --> 00:30:11.000 So let's take a look at router, 0.0.0.5. 00:30:11.000 --> 00:30:14.000 And you'll see here, let's pick this one right here, 00:30:14.000 --> 00:30:17.000 one of those subinterfaces on our branch router. 00:30:17.000 --> 00:30:22.000 10.0.254.0 is over here, if you recall. 00:30:22.000 --> 00:30:23.000 So this is R2. 00:30:23.000 --> 00:30:25.000 Don't forget the Area Border Router. 00:30:25.000 --> 00:30:27.000 So this is a Type 1 LSA right now. 00:30:27.000 --> 00:30:32.000 Let's take this network ID and this subnet mask, 00:30:32.000 --> 00:30:34.000 and let's build a Type 3 for who? 00:30:34.000 --> 00:30:36.000 For Area 0. 00:30:36.000 --> 00:30:40.000 So show IP OSPF database now. 00:30:40.000 --> 00:30:43.000 And so the Type 1 from Area 1, 00:30:43.000 --> 00:30:50.000 we now create a Type 3 of just the network ID for Area 0. 00:30:50.000 --> 00:30:53.000 And I inject that into Area 0. 00:30:53.000 --> 00:31:01.000 So if we look that up, summary, 10.0.254.0, 00:31:01.000 --> 00:31:04.000 you'll see that, hey, I'm router number 2. 00:31:04.000 --> 00:31:06.000 I know about this network. 00:31:06.000 --> 00:31:07.000 That's over here somewhere. 00:31:07.000 --> 00:31:09.000 You don't have to worry about the details. 00:31:10.000 --> 00:31:12.000 And if you want to reach this network, 00:31:12.000 --> 00:31:15.000 just send your traffic to me. 00:31:15.000 --> 00:31:19.000 So let's go to somebody like DSW1. 00:31:19.000 --> 00:31:23.000 And remember, DSW1 only has an Area 0 database. 00:31:23.000 --> 00:31:27.000 So if you just look at DSW1's Area 0 database, 00:31:27.000 --> 00:31:29.000 look what it says. 00:31:29.000 --> 00:31:35.000 I know about 10.0.254.0 slash 24 from router number 2. 00:31:35.000 --> 00:31:38.000 Now, do I know how to get to router number 2? 00:31:38.000 --> 00:31:40.000 Yes or no, folks? 00:31:40.000 --> 00:31:44.000 Does DSW1 know how to get to router number 2? 00:31:44.000 --> 00:31:45.000 Yes or no? 00:31:50.000 --> 00:31:52.000 Based on everything we talked about, 00:31:52.000 --> 00:31:54.000 you should be able to get that answer. 00:31:54.000 --> 00:31:57.000 Does DSW1 know how to get to router number 2? 00:32:03.000 --> 00:32:06.000 Everybody type in yes. 00:32:06.000 --> 00:32:07.000 Yes. 00:32:09.000 --> 00:32:10.000 Okay. 00:32:10.000 --> 00:32:13.000 The question is, how do they know? 00:32:15.000 --> 00:32:16.000 How do they know? 00:32:23.000 --> 00:32:25.000 Type 1, right? 00:32:25.000 --> 00:32:26.000 Type 1. 00:32:26.000 --> 00:32:29.000 Do I know about router number 2? 00:32:29.000 --> 00:32:30.000 Yeah. 00:32:30.000 --> 00:32:33.000 Because they're in the same area, right? 00:32:34.000 --> 00:32:35.000 Yeah. 00:32:36.000 --> 00:32:39.000 So router number 2 tells me about that network, 00:32:39.000 --> 00:32:42.000 tells me if I want to get there to go through it, 00:32:42.000 --> 00:32:46.000 based on my topological map from type 1s and type 2s, 00:32:46.000 --> 00:32:48.000 I know how to get to router number 2. 00:32:48.000 --> 00:32:51.000 Therefore, I can get to 10.0.254.0. 00:32:53.000 --> 00:32:56.000 Just more pieces of the puzzle coming together. 00:32:56.000 --> 00:32:57.000 That's all. 00:32:59.000 --> 00:33:01.000 I know some of your minds right now are getting warped. 00:33:01.000 --> 00:33:02.000 I know. 00:33:03.000 --> 00:33:05.000 Reviewing this a couple of times is good. 00:33:06.000 --> 00:33:08.000 It'll come together more and more. 00:33:09.000 --> 00:33:12.000 So, okay, that's type 3. 00:33:12.000 --> 00:33:13.000 Type 3. 00:33:15.000 --> 00:33:18.000 Oh, one of the things to know, too, about type 3s 00:33:18.000 --> 00:33:21.000 is let's say, let's just do this right now, 00:33:21.000 --> 00:33:24.000 and let's say this is area right now 51, all right? 00:33:24.000 --> 00:33:29.000 And so this is my area border router between area 0 and area 51. 00:33:29.000 --> 00:33:32.000 So when this router injects the type 3 in here, 00:33:32.000 --> 00:33:34.000 it's only for here. 00:33:34.000 --> 00:33:35.000 Remember that. 00:33:36.000 --> 00:33:41.000 So then how does area 51 learn about the networks that are down here, right? 00:33:41.000 --> 00:33:42.000 What network is that? 00:33:42.000 --> 00:33:47.000 That would be one, we said it's 10.0.254.0.24 as an example, 00:33:47.000 --> 00:33:48.000 the one down there. 00:33:48.000 --> 00:33:50.000 How would it know about that? 00:33:50.000 --> 00:33:53.000 Because this area border router would get what? 00:33:53.000 --> 00:33:56.000 That area border router gets the type 3, 00:33:56.000 --> 00:34:02.000 and then it would create a new type 3 for this area. 00:34:02.000 --> 00:34:03.000 That's right. 00:34:03.000 --> 00:34:09.000 So a type 3 can also create a new type 3 for another area 00:34:09.000 --> 00:34:13.000 because the type 3 from this area border router is only good for this area. 00:34:13.000 --> 00:34:17.000 So if you have other area border routers, which you will have in your environment, 00:34:17.000 --> 00:34:20.000 then that area border router takes the type 3 and says, 00:34:20.000 --> 00:34:24.000 oh, I'll generate a new type 3 for my area and say, 00:34:24.000 --> 00:34:27.000 hey, I am this area border router. 00:34:27.000 --> 00:34:29.000 I know about this network. 00:34:29.000 --> 00:34:33.000 If you want to get to it, send the traffic to me, 00:34:33.000 --> 00:34:35.000 just like this one did into here. 00:34:35.000 --> 00:34:38.000 So now, basically, traffic goes from here to here, 00:34:38.000 --> 00:34:41.000 and then this router says, oh, okay, I've got to route you over to here. 00:34:41.000 --> 00:34:43.000 Then this router routes it back inside. 00:34:43.000 --> 00:34:48.000 It's almost, almost, as you can see here, becoming distance vector-like, 00:34:48.000 --> 00:34:52.000 as opposed, yeah, it is. 00:34:52.000 --> 00:34:54.000 When you start adding more areas, 00:34:54.000 --> 00:34:59.000 it kind of starts being distance vector-like more than link state. 00:34:59.000 --> 00:35:00.000 Just a little bit. 00:35:00.000 --> 00:35:01.000 Just a little bit. 00:35:01.000 --> 00:35:03.000 Because now you're routing based on what? 00:35:03.000 --> 00:35:09.000 Router rumors, router haunts, different things like that. 00:35:09.000 --> 00:35:10.000 All right. 00:35:10.000 --> 00:35:13.000 So that is your type 3. 00:35:13.000 --> 00:35:15.000 Generated by who again? 00:35:15.000 --> 00:35:17.000 Area border routers. 00:35:17.000 --> 00:35:19.000 Good. 00:35:19.000 --> 00:35:22.000 Describing routes outside of your area, 00:35:22.000 --> 00:35:27.000 but still within your routing domain. 00:35:27.000 --> 00:35:31.000 So if we go to DSW-1, look at the routing table again. 00:35:31.000 --> 00:35:40.000 Still within the OSPF routing domain, but in a different area. 00:35:40.000 --> 00:35:42.000 Next, I'm going to skip 4. 00:35:42.000 --> 00:35:46.000 We're going to come back to 4 after. 00:35:46.000 --> 00:35:49.000 Let's talk about 5. 00:35:49.000 --> 00:35:54.000 5, first and foremost, is generated by who? 00:35:54.000 --> 00:35:59.000 It's going to be generated by autonomous system boundary routers. 00:35:59.000 --> 00:36:05.000 Now, what makes you an autonomous system boundary router again? 00:36:05.000 --> 00:36:13.000 The command default information originate or any type of redistribution. 00:36:13.000 --> 00:36:15.000 So if you go back to R1, 00:36:15.000 --> 00:36:18.000 notice it says you are an autonomous system boundary router. 00:36:18.000 --> 00:36:19.000 Why? 00:36:19.000 --> 00:36:20.000 Because, remember, on R1, 00:36:20.000 --> 00:36:26.000 we typed in default information originate earlier in today's session. 00:36:26.000 --> 00:36:31.000 If we go to somebody like R2 and we type in show IP protocols, 00:36:31.000 --> 00:36:34.000 notice it says you are an area border router 00:36:34.000 --> 00:36:37.000 and you are an autonomous system boundary router. 00:36:37.000 --> 00:36:40.000 So you could be more than one type. 00:36:40.000 --> 00:36:42.000 Why am I both in this case? 00:36:42.000 --> 00:36:46.000 Well, I'm an area border router connecting area 0 to area 1. 00:36:46.000 --> 00:36:51.000 But don't forget, we also typed in default information originate on this router 00:36:51.000 --> 00:36:53.000 as well because it connects us to the Internet, 00:36:53.000 --> 00:36:58.000 making me an autonomous system boundary router. 00:36:58.000 --> 00:37:06.000 So the ASBR is taking networks that are outside of our routing domain. 00:37:06.000 --> 00:37:12.000 So, for example, the default route is to all networks outside your routing domain. 00:37:12.000 --> 00:37:15.000 So that would be a type 5 LSA. 00:37:15.000 --> 00:37:17.000 Networks outside of your routing domain, 00:37:17.000 --> 00:37:23.000 external to your routing domain, are type 5s. 00:37:23.000 --> 00:37:26.000 So that could be routes we redistributed. 00:37:26.000 --> 00:37:32.000 So let's say up here we were running EIGRP. 00:37:32.000 --> 00:37:39.000 So this router right here is running both EIGRP and OSPF. 00:37:39.000 --> 00:37:47.000 So let's say we had the network 192.168.255.0.24 up here. 00:37:47.000 --> 00:37:49.000 How would I get that into OSPF? 00:37:49.000 --> 00:37:53.000 I would do redistribution, which is not on this exam. 00:37:53.000 --> 00:37:55.000 So don't worry about this for the exam. 00:37:55.000 --> 00:37:57.000 I'm just trying to give you some real-world knowledge here. 00:37:57.000 --> 00:38:00.000 I would redistribute that on the router into OSPF. 00:38:00.000 --> 00:38:05.000 Okay, when I do that, this network here in OSPF would be, for example, 00:38:05.000 --> 00:38:17.000 E2 192.168.255.0.24, E2, OSPF, external route, outside of my routing domain. 00:38:17.000 --> 00:38:18.000 I redistributed it in. 00:38:18.000 --> 00:38:19.000 It doesn't belong to me. 00:38:19.000 --> 00:38:22.000 It belongs to somebody else outside of OSPF. 00:38:22.000 --> 00:38:24.000 Okay, same thing with default information originate. 00:38:24.000 --> 00:38:28.000 You're taking 0.0.0.0.0 and you are bringing it in. 00:38:28.000 --> 00:38:30.000 That's what you're doing. 00:38:30.000 --> 00:38:36.000 So that's why you are generating these type 5s in those different types of scenarios. 00:38:36.000 --> 00:38:41.000 Routes outside of your routing domain through redistribution 00:38:41.000 --> 00:38:44.000 and through default information originate. 00:38:44.000 --> 00:38:49.000 So what happens with a type 5 is it gets generated by that Autonomous System 00:38:49.000 --> 00:38:52.000 Boundary Router and then shipped in to the routing domain, 00:38:52.000 --> 00:38:56.000 shipped in to the routing domain. 00:38:56.000 --> 00:39:02.000 So now Area 0 is going to learn all about it, 00:39:02.000 --> 00:39:04.000 and Area 1 is going to learn all about it. 00:39:04.000 --> 00:39:14.000 So if we look at our database, for example, on DSW1, 00:39:14.000 --> 00:39:23.000 we'll see in our database that this is the one we've learned from R2, 00:39:23.000 --> 00:39:29.000 0.0.0.0 from R2. 00:39:29.000 --> 00:39:42.000 And if we crack that open, it's external, 0.0.0.2, 0.0.0.0. 00:39:42.000 --> 00:39:48.000 All right, we'll see that we have the one from R2 listed down here. 00:39:48.000 --> 00:39:50.000 All right, so it's 0.0.0.0. 00:39:50.000 --> 00:39:52.000 Sorry, 0.0.0.0. 00:39:52.000 --> 00:39:55.000 Something math slash 0. 00:39:55.000 --> 00:39:56.000 And the metric type is 2. 00:39:56.000 --> 00:39:57.000 That means E2. 00:39:57.000 --> 00:39:59.000 That's the E2 right there. 00:39:59.000 --> 00:40:09.000 So ASBR, redistribution, default routes. 00:40:09.000 --> 00:40:10.000 Sorry. 00:40:10.000 --> 00:40:14.000 Yeah, redistribution or default information originate for default routes, 00:40:15.000 --> 00:40:22.000 produces type 5s, and they're right at the very bottom every time. 00:40:22.000 --> 00:40:28.000 Let's go over to branch, take a peek at branch. 00:40:28.000 --> 00:40:30.000 And you'll see the same thing over here. 00:40:30.000 --> 00:40:32.000 We learned it from R1 and R2 as well. 00:40:32.000 --> 00:40:36.000 So with that said, right, we learned it from R2. 00:40:36.000 --> 00:40:39.000 Why did we also learn it from R1? 00:40:39.000 --> 00:40:40.000 You see that? 00:40:40.000 --> 00:40:45.000 We learned it from R1 because what we need to realize here is that when you 00:40:45.000 --> 00:40:50.000 inject a type 5 LSA, it goes everywhere in that area, 00:40:50.000 --> 00:40:53.000 it eventually reaches an ABR, 00:40:53.000 --> 00:41:05.000 and that ABR sends it into any other area unmodified, unmodified, 00:41:05.000 --> 00:41:22.000 meaning that this router actually received the type 5 LSA that R1 created. 00:41:22.000 --> 00:41:29.000 Now, let me ask you this question. 00:41:29.000 --> 00:41:35.000 This is very important. 00:41:35.000 --> 00:41:43.000 We're focused on this scenario right here right now. 00:41:43.000 --> 00:41:50.000 Type 5 generated by R1 just flooded right into area 1. 00:41:50.000 --> 00:41:54.000 So R1 sees 0.0.0. 00:41:54.000 --> 00:41:55.000 Sorry, did I say R1? 00:41:55.000 --> 00:42:07.000 I meant branch A, which is R5, in our case, 0.0.0.0.0 via R1. 00:42:07.000 --> 00:42:09.000 That's what this means. 00:42:09.000 --> 00:42:15.000 That's what we're seeing in this example. 00:42:15.000 --> 00:42:30.000 It says here 0.0.0.0 via R1. 00:42:31.000 --> 00:42:38.000 Does branch A, R router 0.0.0.5, 00:42:38.000 --> 00:42:46.000 does this router even know that R1 exists? 00:42:46.000 --> 00:43:00.000 Yes or no based on everything I've taught you so far in this discussion? 00:43:00.000 --> 00:43:10.000 Does that router even know that R1 exists? 00:43:10.000 --> 00:43:13.000 No. 00:43:13.000 --> 00:43:28.000 Because which LSA teaches you about a router's existence? 00:43:28.000 --> 00:43:29.000 Type 1. 00:43:29.000 --> 00:43:43.000 Is R5 ever going to get a type 1 LSA from R1? 00:43:43.000 --> 00:43:45.000 Well, I guess it's broken, right? 00:43:45.000 --> 00:43:46.000 And it is. 00:43:46.000 --> 00:43:48.000 It totally is broken. 00:43:48.000 --> 00:43:56.000 There's no way that that router can now use that exit point. 00:43:56.000 --> 00:44:03.000 So here I come to save the day. 00:44:03.000 --> 00:44:13.000 Type 4 LSA to save the day. 00:44:13.000 --> 00:44:18.000 The type 4 LSA, folks, is called the ASBR summary LSA. 00:44:18.000 --> 00:44:20.000 That doesn't mean anything. 00:44:20.000 --> 00:44:24.000 It's bad naming again. 00:44:24.000 --> 00:44:28.000 Type 4 is a Band-Aid LSA. 00:44:28.000 --> 00:44:32.000 It's to fix this exact problem I am teaching you about right now. 00:44:32.000 --> 00:44:39.000 So remember, this type 5 LSA gets injected, gets flooded right into this area. 00:44:39.000 --> 00:44:46.000 So this router here sees 0.0.0.0 via R5. 00:44:47.000 --> 00:44:50.000 Via R1, sorry. 00:44:50.000 --> 00:44:57.000 Like we see in our topology right here. 00:44:57.000 --> 00:44:58.000 Right there. 00:44:58.000 --> 00:45:02.000 0.0.0.0 via R1, all right? 00:45:02.000 --> 00:45:05.000 The type 4 is generated by who? 00:45:05.000 --> 00:45:08.000 Generated by the ABR. 00:45:08.000 --> 00:45:13.000 Remember that. 00:45:13.000 --> 00:45:16.000 The ABR creates this because of this situation. 00:45:16.000 --> 00:45:30.000 As soon as this situation happens, it then generates a type 4 and says R1 via R2 in this example. 00:45:30.000 --> 00:45:32.000 That's it. 00:45:32.000 --> 00:45:38.000 So now you've got the type 5 that says this. 00:45:38.000 --> 00:45:41.000 You've got the type 4 that says this. 00:45:41.000 --> 00:45:45.000 You've got the type 1 that tells you how to get to R2. 00:45:45.000 --> 00:45:55.000 It's going to take three LSAs to make this work. 00:45:55.000 --> 00:46:04.000 So right now we have our type 5 that says 0.0.0.0 via R1. 00:46:04.000 --> 00:46:06.000 Look at the type 4. 00:46:06.000 --> 00:46:16.000 The type 4 that was generated by the area border router, it says 0.0.0.1 is via R2. 00:46:16.000 --> 00:46:25.000 And then I have my R2 LSA that helps me get to R2. 00:46:25.000 --> 00:46:33.000 A combination of type 5, type 4, and type 1 to make sure we can get there. 00:46:33.000 --> 00:46:35.000 A lot of puzzle pieces, as I said. 00:46:35.000 --> 00:46:36.000 A lot of puzzle pieces. 00:46:36.000 --> 00:46:45.000 So notice, though, that we don't have a type 4 for the type 5 LSA that's generated right here. 00:46:45.000 --> 00:46:46.000 You see that? 00:46:46.000 --> 00:46:51.000 We have 0.0.0.0 via 0.0.0.2. 00:46:51.000 --> 00:46:55.000 Why do I not need a type 4 for this one? 00:46:55.000 --> 00:47:02.000 I don't need a type 4 for this one because I know how to get to R2 because R2 is in my area. 00:47:02.000 --> 00:47:15.000 So if the ASBR is not in your area, the area border router will generate a type 4 to tell you where it is. 00:47:15.000 --> 00:47:21.000 So that way there you can get to it. 00:47:21.000 --> 00:47:29.000 So Conrad is asking, can't branch A see how to get to R1 via type 3 LSA? 00:47:29.000 --> 00:47:33.000 Okay, so what is inside the type 3 LSA? 00:47:33.000 --> 00:47:43.000 What is inside the type 3 LSA is the network ID and the area border router to get there. 00:47:43.000 --> 00:47:44.000 That's it. 00:47:44.000 --> 00:47:45.000 There's nothing else. 00:47:45.000 --> 00:47:53.000 So, for example, these are all your type 3s that are coming into area 1 from area 0. 00:47:53.000 --> 00:47:54.000 By who? 00:47:54.000 --> 00:47:58.000 Router 2, router 2, router 2, router 2, router 2, the area border router. 00:47:58.000 --> 00:48:09.000 So if we open up any one of these, show IP OSPF database for summary. 00:48:09.000 --> 00:48:14.000 Network 10.0.0.0 size 24 is reachable via me, R2, that's it. 00:48:14.000 --> 00:48:21.000 So there's nothing in there that will ever, ever, ever tell how to get to R1. 00:48:21.000 --> 00:48:25.000 So even let's pick something like one of R1's networks. 00:48:25.000 --> 00:48:27.000 So R1 is on this network right here. 00:48:27.000 --> 00:48:28.000 It's connected to that network. 00:48:28.000 --> 00:48:31.000 So let's go ahead and look at that one instead. 00:48:31.000 --> 00:48:32.000 So it would be what? 00:48:32.000 --> 00:48:34.000 10.40.23.8. 00:48:34.000 --> 00:48:40.000 That's a network that R1 is connected to. 00:48:40.000 --> 00:48:43.000 It says 10.40.23.8 is reachable via me, R2. 00:48:43.000 --> 00:48:44.000 That's it. 00:48:44.000 --> 00:48:45.000 Nothing else. 00:48:45.000 --> 00:48:48.000 Has no idea, Conrad. 00:48:48.000 --> 00:48:52.000 So, no, not the type 3 LSA. 00:48:53.000 --> 00:48:57.000 Type 3 LSA is just about describing networks that live in a different area. 00:48:57.000 --> 00:48:59.000 That's it. 00:48:59.000 --> 00:49:01.000 So here's the way to think about it. 00:49:01.000 --> 00:49:11.000 So if this is area 0 right now, and these are our four routers, 00:49:11.000 --> 00:49:14.000 they see everything that's going on between them. 00:49:14.000 --> 00:49:17.000 They see everything that's going on. 00:49:17.000 --> 00:49:20.000 So they all see this. 00:49:20.000 --> 00:49:22.000 Now, what do they see over here? 00:49:22.000 --> 00:49:24.000 What do they see over here? 00:49:24.000 --> 00:49:28.000 They see that over here, let's try this. 00:49:28.000 --> 00:49:32.000 They see that over here, something's over here. 00:49:32.000 --> 00:49:34.000 Something's over here. 00:49:34.000 --> 00:49:38.000 With 10.0.254.0, size 24. 00:49:38.000 --> 00:49:41.000 10.0.255.0, size 24. 00:49:41.000 --> 00:49:43.000 They know that 10.0. 00:49:43.000 --> 00:49:45.000 Okay, you see the difference? 00:49:45.000 --> 00:49:49.000 In area 0, they know all the details of all the links, 00:49:49.000 --> 00:49:52.000 of all the interfaces, of all the routers. 00:49:52.000 --> 00:49:56.000 But then beyond R2, what do they see? 00:49:56.000 --> 00:49:59.000 Just a fluffy cloud with a whole bunch of networks. 00:49:59.000 --> 00:50:02.000 And then over here, they also see that R2 can get us out to the thing 00:50:02.000 --> 00:50:05.000 called the crazy Internet because it's 0.0.0.0. 00:50:05.000 --> 00:50:06.000 There you go. 00:50:06.000 --> 00:50:07.000 That's all they see. 00:50:07.000 --> 00:50:11.000 They see the details of their area, and then every other area is just a big, 00:50:11.000 --> 00:50:15.000 poofy, fluffy cloud with network IDs in it. 00:50:15.000 --> 00:50:16.000 And so you want to go over there? 00:50:16.000 --> 00:50:17.000 Go through that area of border router. 00:50:17.000 --> 00:50:18.000 You want to go over there? 00:50:18.000 --> 00:50:19.000 Go through that area of border router. 00:50:19.000 --> 00:50:20.000 You want to go over there? 00:50:20.000 --> 00:50:21.000 Go through that. 00:50:21.000 --> 00:50:23.000 So outside of your area, you don't know the details. 00:50:23.000 --> 00:50:24.000 You don't know nothing. 00:50:24.000 --> 00:50:28.000 You just know they exist. 00:50:28.000 --> 00:50:30.000 That is OSPF design. 00:50:30.000 --> 00:50:32.000 That is OSPF configuration. 00:50:32.000 --> 00:50:37.000 That is OSPF's link state database. 00:50:37.000 --> 00:50:39.000 Yep. 00:50:39.000 --> 00:50:41.000 Okay, so now that we understand our LSAs, 00:50:41.000 --> 00:50:45.000 let's wrap this up by having a discussion on OSPF's metric. 00:50:45.000 --> 00:50:50.000 So OSPF's metric is called cost, 00:50:50.000 --> 00:50:53.000 and the cost is based on interface bandwidth. 00:50:53.000 --> 00:50:56.000 So every single one of our interfaces are going to have a cost associated 00:50:56.000 --> 00:50:57.000 with them. 00:50:57.000 --> 00:51:00.000 So if we go out to, for example, like DSW1, 00:51:00.000 --> 00:51:05.000 we type in show IP OSPF interface brief, 00:51:05.000 --> 00:51:08.000 you'll see that we have a cost, cost, cost, cost, cost, cost, 00:51:08.000 --> 00:51:11.000 cost associated with every single one of our interfaces. 00:51:11.000 --> 00:51:12.000 So that is true. 00:51:12.000 --> 00:51:14.000 When you enable OSPF on an interface, 00:51:14.000 --> 00:51:17.000 it figures out the cost of that particular interface. 00:51:17.000 --> 00:51:21.000 And so how is the cost figured out on an interface-by-interface basis? 00:51:21.000 --> 00:51:25.000 It uses this calculation right here. 00:51:25.000 --> 00:51:30.000 Reference bandwidth, which is a number that is set in the operating system, 00:51:30.000 --> 00:51:33.000 by default on our version of iOS, 00:51:33.000 --> 00:51:38.000 it's going to be, if we type in show IP OSPF, that's it. 00:51:38.000 --> 00:51:39.000 Just show IP OSPF. 00:51:39.000 --> 00:51:43.000 You scroll down, you'll see here reference bandwidth is 100 megabits per 00:51:43.000 --> 00:51:44.000 second. 00:51:44.000 --> 00:51:47.000 Reference bandwidth is 100 megabits per second. 00:51:47.000 --> 00:51:52.000 So that is the number by default on this platform. 00:51:52.000 --> 00:51:59.000 So you've got 100 megabits per second divided by, 00:51:59.000 --> 00:52:02.000 divided by interface bandwidth. 00:52:02.000 --> 00:52:05.000 So let's say we have a 10 megabit per second interface, 00:52:05.000 --> 00:52:07.000 then our cost would be 10. 00:52:07.000 --> 00:52:10.000 That would be your cost, right? 00:52:10.000 --> 00:52:14.000 So if you have 100 megabit reference bandwidth divided by 100 meg 00:52:14.000 --> 00:52:16.000 interface, your cost is 1. 00:52:16.000 --> 00:52:20.000 If you have 100 reference bandwidth divided by a 1 gig interface, 00:52:20.000 --> 00:52:23.000 your cost is 0.1, which equals 1. 00:52:23.000 --> 00:52:29.000 If you had a reference bandwidth of 100 and you had a 10 gig interface, 00:52:29.000 --> 00:52:31.000 that's 0.01. 00:52:31.000 --> 00:52:32.000 Therefore, your cost is 1. 00:52:32.000 --> 00:52:34.000 Okay, we've got a problem here, don't we? 00:52:34.000 --> 00:52:36.000 Yeah, we do. 00:52:36.000 --> 00:52:37.000 And the problem is, 00:52:37.000 --> 00:52:40.000 is that once you get over a fast Ethernet interface with a default 00:52:40.000 --> 00:52:42.000 reference bandwidth, this gets all messed up. 00:52:42.000 --> 00:52:47.000 Every single one of our high-speed interfaces from 100 megs and up are 00:52:47.000 --> 00:52:49.000 all treated the exact same way. 00:52:49.000 --> 00:52:53.000 So if we go over to router number 2 right now, 00:52:53.000 --> 00:52:55.000 if we visit router number 2, 00:52:55.000 --> 00:52:59.000 we can actually see this because I have a fast Ethernet interface there. 00:52:59.000 --> 00:53:03.000 So show IP OSPF interface brief. 00:53:03.000 --> 00:53:07.000 When we look at this output, 00:53:07.000 --> 00:53:11.000 you'll see my gig interfaces and my fast Ethernet interfaces all have a 00:53:11.000 --> 00:53:12.000 cost of 1. 00:53:12.000 --> 00:53:15.000 So you are definitely going to want to take the time to manipulate the 00:53:15.000 --> 00:53:18.000 cost, sorry, manipulate the reference bandwidth. 00:53:18.000 --> 00:53:22.000 So that way there you have a more accurate cost calculation in your 00:53:22.000 --> 00:53:26.000 environment because you don't want interfaces to be treated the same when 00:53:26.000 --> 00:53:28.000 it comes to cost if they're not the same. 00:53:28.000 --> 00:53:32.000 Because right now it thinks that the fast Ethernet interface is the same 00:53:32.000 --> 00:53:35.000 speed as the gigabit Ethernet interface, which is not. 00:53:35.000 --> 00:53:36.000 So to do that, 00:53:36.000 --> 00:53:38.000 you're going to want to change your reference bandwidth to a value that 00:53:38.000 --> 00:53:41.000 makes sense in your case, so router OSPF 1. 00:53:41.000 --> 00:53:44.000 So just to show you, if I type in auto cost reference bandwidth, 00:53:44.000 --> 00:53:48.000 we'll get, I'll pick a value like 1,000, 00:53:48.000 --> 00:53:51.000 1,000 megabits per second, which equals a 1 gig interface. 00:53:51.000 --> 00:53:57.000 So now if we look at the output of new show IP OSPF interface brief, 00:53:57.000 --> 00:54:00.000 you'll see here that now the fast Ethernet has a cost of 10 and gig has a 00:54:00.000 --> 00:54:02.000 cost of one still, why? 00:54:02.000 --> 00:54:04.000 Because 1,000 divided by 1,000 is 1, 00:54:04.000 --> 00:54:06.000 1,000 divided by a hundred is 10. 00:54:06.000 --> 00:54:09.000 So let's add one more zero to that just for show. 00:54:09.000 --> 00:54:12.000 And if we look at the output, you'll see that the cost is now 10, 00:54:12.000 --> 00:54:13.000 10 and whatever. 00:54:13.000 --> 00:54:16.000 Let's pick the maximum value possible with auto cost reference bandwidth, 00:54:16.000 --> 00:54:20.000 just to show you that let's pick that as the highest possible value we could 00:54:20.000 --> 00:54:21.000 use. 00:54:21.000 --> 00:54:23.000 And now you'll see that the reference bandwidth of the interface is that. 00:54:23.000 --> 00:54:27.000 So does it make sense that you should do this on all your routers and put the 00:54:27.000 --> 00:54:29.000 exact same number on all your routers? 00:54:29.000 --> 00:54:30.000 Yes. 00:54:30.000 --> 00:54:34.000 It even tells us that make sure it's consistent across all routers or else 00:54:34.000 --> 00:54:36.000 you're not going to have, you might have suboptimal routing. 00:54:39.000 --> 00:54:44.000 So one thing note is that many of you nowadays could use this maximum value, 00:54:44.000 --> 00:54:46.000 set it, forget it and move on. 00:54:46.000 --> 00:54:50.000 But what you need to realize is that if you still have slow speed interfaces, 00:54:51.000 --> 00:54:53.000 interfaces that are like 10 megs or less, 00:54:53.000 --> 00:54:55.000 and it's really actually just a little bit more than 10 megs, 00:54:55.000 --> 00:54:59.000 but let's say 10 megs or less in your environment that you can't use that 00:54:59.000 --> 00:55:04.000 number because this maxes out at 65,535. 00:55:04.000 --> 00:55:07.000 That's the max cost you can have on your interface. 00:55:07.000 --> 00:55:12.000 So if the max cost is 65,535, look a fast seat and interface is 42,000. 00:55:12.000 --> 00:55:17.000 That means a 10 meg interface would be 422 megs. 00:55:21.000 --> 00:55:22.000 Which is more than 65,000, 00:55:24.000 --> 00:55:28.000 which means a 1.544 megabit per second interface would be like in the 00:55:28.000 --> 00:55:31.000 millions. Again, you can't have that. 00:55:32.000 --> 00:55:33.000 It maxes out. 00:55:33.000 --> 00:55:37.000 So if you use that top value and you have interfaces from like, 00:55:37.000 --> 00:55:43.000 I would say 75 megs or even 60 megs. 00:55:43.000 --> 00:55:47.000 So 60 meg ethernet and slower, 00:55:47.000 --> 00:55:51.000 they would all max out at 65,535 and you don't want that either. 00:55:51.000 --> 00:55:54.000 So although this may seem like the best option, 00:55:54.000 --> 00:55:56.000 not good on the other side of things. 00:55:56.000 --> 00:56:01.000 So essentially find a value that works based on your slowest speed interface 00:56:01.000 --> 00:56:05.000 and your organization and the maximum speed interface in your organization. 00:56:05.000 --> 00:56:09.000 If the slowest speed interface you have is 10 megs, then maybe, you know, 00:56:09.000 --> 00:56:13.000 doing something like this would make more sense. Maybe, I don't know. 00:56:13.000 --> 00:56:14.000 I'd have to do the math, but yeah. 00:56:15.000 --> 00:56:19.000 So now your 10 meg interface would be like 420, 00:56:19.000 --> 00:56:25.000 sorry, 42,949 is what your 10 meg interface would be. 00:56:25.000 --> 00:56:28.000 But maybe this doesn't work at your high speed interfaces anymore. 00:56:28.000 --> 00:56:32.000 So it's about figuring out what works for the high speed, low speed, 00:56:32.000 --> 00:56:34.000 getting the number that works in between. Most of us though, 00:56:34.000 --> 00:56:37.000 we could probably go with the highest possible value. Everything's fine. 00:56:39.000 --> 00:56:41.000 But in the grand scheme of things, right. 00:56:41.000 --> 00:56:43.000 Figuring out what's my high speed interface right now. 00:56:43.000 --> 00:56:45.000 We got like 10 gigs. Okay. 00:56:45.000 --> 00:56:48.000 So 10 gigs would be this value here. Okay. 00:56:48.000 --> 00:56:52.000 Well, when are you switching to a hundred gigs? When's that going to happen? 00:56:52.000 --> 00:56:55.000 How many years from now? Right. If you add on another zero, 00:56:55.000 --> 00:56:57.000 there's for a hundred gig interface that might work for you across the board 00:56:57.000 --> 00:57:00.000 for all of your interfaces for the next like 10 years. 00:57:00.000 --> 00:57:03.000 So what you pick is up to you. There's no right or wrong answer. 00:57:03.000 --> 00:57:04.000 It's just, 00:57:04.000 --> 00:57:09.000 let's make sure that our interfaces are not all coming up with the exact same 00:57:09.000 --> 00:57:12.000 cost. We want them to be gigabit to have the same cost. 00:57:12.000 --> 00:57:14.000 We want 10 gig to have their own unique costs. 00:57:14.000 --> 00:57:16.000 We want fast Ethernet to have their own unique costs. 00:57:16.000 --> 00:57:18.000 Let's make sure they're not all defaulting to one. 00:57:18.000 --> 00:57:21.000 Like we just saw here in our environment. So for today, 00:57:21.000 --> 00:57:25.000 I'm just going to change it to 10,000 on all of my routers. 00:57:29.000 --> 00:57:31.000 Did I say 10,000? I mean, 1,000. 00:57:36.000 --> 00:57:40.000 So that way there we can do our little demo that I want to do now. 00:57:43.000 --> 00:57:44.000 Okay. 00:57:56.000 --> 00:58:01.000 So now that we have that information and we take now a peek back at our 00:58:01.000 --> 00:58:06.000 topology, what is, how is cost going to be calculated? 00:58:06.000 --> 00:58:10.000 What cost is cumulative? Cost is cumulative. 00:58:10.000 --> 00:58:13.000 That's what it is. So when it comes to cost, 00:58:21.000 --> 00:58:24.000 we are going to have costs for every single one of our interfaces. 00:58:24.000 --> 00:58:29.000 So this is now 10. This is now 10. This is now 10. This is one. 00:58:29.000 --> 00:58:32.000 This is one. This is one. Let's not forget about our SVIs. 00:58:32.000 --> 00:58:36.000 This is going to be one, right? This is going to be one. 00:58:36.000 --> 00:58:37.000 This is going to be one. This is going to be one. 00:58:37.000 --> 00:58:39.000 This is going to be one. Why? 00:58:39.000 --> 00:58:41.000 Because I made the reference band 1,000 on all of them. 00:58:42.000 --> 00:58:45.000 So let's think about this network down here. 10.0.0. 00:58:47.000 --> 00:58:51.000 10.0.254.0 slash 24. Okay. 00:58:52.000 --> 00:58:56.000 So in this environment here, we're going to be exchanging type one LSAs. 00:58:57.000 --> 00:59:02.000 So what happens here is R2 learns about this network from that router. 00:59:03.000 --> 00:59:07.000 And that router says 10.0.254.0 slash 24 has a cost of 10. 00:59:10.000 --> 00:59:11.000 That's what it says. 00:59:12.000 --> 00:59:16.000 So if we look at that particular do show IP OSTF database for routers, 00:59:25.000 --> 00:59:28.000 0.0.0.5 me, right? 00:59:29.000 --> 00:59:32.000 What are we going to see? Let's go find that network. It says 10. 00:59:33.000 --> 00:59:36.000 So when it advertises that to R2, that's what R2 learns. 00:59:37.000 --> 00:59:40.000 So if we go take a look at the exact same output on R2, 00:59:44.000 --> 00:59:48.000 R2 sees that the value is going to be 10, right? 00:59:50.000 --> 00:59:54.000 So R2 now has that information. What does R2 do now? 00:59:55.000 --> 00:59:59.000 Well, R2 taking the type one and type two LSAs builds a topological map. 01:00:01.000 --> 01:00:04.000 And it says, okay, so it's my cost of my interface is 10. 01:00:06.000 --> 01:00:10.000 And that gets me all the way over to that router that advertised it to me. 01:00:12.000 --> 01:00:16.000 So what does that mean? It means I can now add 10 plus 10, 01:00:18.000 --> 01:00:21.000 which would give me a cost of 20 in this particular case. 01:00:21.000 --> 01:00:25.000 So it's this number, this number plus this number. 01:00:27.000 --> 01:00:31.000 It's always the exiting interface that's used for the calculation. 01:00:32.000 --> 01:00:33.000 So if we go to R2 right now, 01:00:33.000 --> 01:00:37.000 we've got 10 and we calculated using the type one LSAs, 01:00:37.000 --> 01:00:40.000 how to get to that router. 01:00:41.000 --> 01:00:43.000 So type one, type two LSAs, dykes are short of passive algorithm. 01:00:43.000 --> 01:00:47.000 We figure out the calculation and we should have a grand total of 20. 01:00:47.000 --> 01:00:49.000 So we look at our routing table, do show IP OSTF database. 01:00:49.000 --> 01:00:53.000 We're going to see that the grand total is drum roll, please 20. 01:00:54.000 --> 01:00:56.000 There it is 20. All right. 01:00:56.000 --> 01:01:00.000 So now let's think about it from the perspective of type three. 01:01:01.000 --> 01:01:04.000 So now what is R2 going to, okay. So let me rephrase that. 01:01:04.000 --> 01:01:07.000 That is what happens in your area. So even over here, right? 01:01:07.000 --> 01:01:10.000 When R2 is trying to understand how to get to these networks or R1 is trying 01:01:10.000 --> 01:01:12.000 to understand how to get to all the networks, same idea. 01:01:13.000 --> 01:01:15.000 I learn about the exact network from you. 01:01:15.000 --> 01:01:17.000 And with the metric of that interface, 01:01:17.000 --> 01:01:20.000 and then I have to figure out how to get to you using type ones and type 01:01:20.000 --> 01:01:21.000 twos, 01:01:21.000 --> 01:01:24.000 and then add up all the costs of the exiting interfaces. 01:01:24.000 --> 01:01:27.000 Once I figure that out and that is the total cost to get to that 01:01:27.000 --> 01:01:29.000 network. So that's what happens inside your area. 01:01:29.000 --> 01:01:32.000 Now, what about between areas? So for example, 01:01:32.000 --> 01:01:35.000 R2 now injects what? A type three LSA. 01:01:36.000 --> 01:01:38.000 So that's what happens inside your area. 01:01:38.000 --> 01:01:40.000 Now what about between areas? So for example, 01:01:40.000 --> 01:01:43.000 R2 now injects what? A type three LSA. 01:01:44.000 --> 01:01:48.000 What does the type three LSA say? Well, where does it go? 01:01:48.000 --> 01:01:50.000 It gets flooded to everybody in the area. 01:01:50.000 --> 01:01:57.000 So now DSW one gets it and says 10.0.254.0 slash 24. 01:01:57.000 --> 01:01:58.000 And what is the metric? 01:01:59.000 --> 01:02:03.000 The metric it learns is going to be this metric right here. 01:02:03.000 --> 01:02:07.000 20 equals 20 from R2. 01:02:08.000 --> 01:02:10.000 And we can look at that right now. 01:02:10.000 --> 01:02:12.000 If we go over to somebody like DSW one as an example, 01:02:13.000 --> 01:02:18.000 do show I P O S P F database summary LSA. 01:02:18.000 --> 01:02:21.000 And then we type in zero dot zero dot no, no, no, no. 01:02:21.000 --> 01:02:24.000 We type in 10.0.254.0. 01:02:25.000 --> 01:02:30.000 And we'll see the final total 10.0.254.0 slash 24 metric equals 20. 01:02:30.000 --> 01:02:35.000 That's the type three LSA that DSW one got from who from R2. 01:02:36.000 --> 01:02:38.000 So now what does DSW one have to do? 01:02:38.000 --> 01:02:42.000 DSW one has to use its topological database that it's already created. 01:02:42.000 --> 01:02:43.000 It's already calculated. 01:02:44.000 --> 01:02:52.000 And it's topological database says from me to you from me to you is what? 01:02:52.000 --> 01:02:54.000 Well, it's my interface cost is one. 01:02:55.000 --> 01:02:57.000 And in this case, that gets me directly to you. 01:02:58.000 --> 01:03:03.000 So I have one plus the 20. 01:03:04.000 --> 01:03:06.000 And now I have the total value in that case. 01:03:06.000 --> 01:03:14.000 So if we go over to DSW one, we type in do show I P route. 01:03:14.000 --> 01:03:16.000 One plus 20 is 21. 01:03:19.000 --> 01:03:20.000 And there it is. 01:03:21.000 --> 01:03:22.000 That's how it's calculated. 01:03:24.000 --> 01:03:30.000 And when it comes to, for example, the external routes, if it's an E2 route, 01:03:31.000 --> 01:03:36.000 whatever the metric is that is injected by the autonomous system boundary router, 01:03:37.000 --> 01:03:41.000 it stays that way and never gets modified in the environment. 01:03:41.000 --> 01:03:42.000 That's right. 01:03:42.000 --> 01:03:49.000 So in this case, R2 put a metric of one when we did the default information originate, 01:03:49.000 --> 01:03:54.000 and it never gets modified or changed or cumulative or added. 01:03:55.000 --> 01:03:56.000 That's the point of E2. 01:03:57.000 --> 01:03:59.000 The metric doesn't change at all. 01:04:00.000 --> 01:04:03.000 It stays at whatever the ASBR made it. 01:04:04.000 --> 01:04:09.000 E1, on the other hand, changes the metric and makes it cumulative. 01:04:09.000 --> 01:04:11.000 So that's the big difference between E1 and E2. 01:04:12.000 --> 01:04:17.000 E2, the metric never changes, whereas E1, the metric is cumulative. 01:04:18.000 --> 01:04:21.000 So like I said earlier, when I talked about E1 and E2, why? 01:04:21.000 --> 01:04:22.000 Why does that happen? 01:04:22.000 --> 01:04:23.000 To give you flexibility. 01:04:23.000 --> 01:04:29.000 If you want to control the ASBR exit points and what your routers use to make the decisions on who to use 01:04:29.000 --> 01:04:32.000 in regards to an exit point, you got a choice. 01:04:32.000 --> 01:04:36.000 You can do E2, manipulate the metric at the entry point, make those adjustments, 01:04:36.000 --> 01:04:40.000 or you can use E1 and let your internal network cumulative costs figure that out for you. 01:04:41.000 --> 01:04:46.000 That's all flexibility that we cover in the advanced routing course NRC 300-410. 01:04:47.000 --> 01:04:49.000 That is not relevant for this particular certification exam. 01:04:50.000 --> 01:04:57.000 So that, my friends, folks, is OSPF costs when it comes to OSPF plus our LSAs. 01:04:57.000 --> 01:05:02.000 So make sure you're aware of how that all happens to make sure you ace the certification exam.