WEBVTT 00:00:01.000 --> 00:00:09.000 Now, it is time to begin OSPF. 00:00:09.000 --> 00:00:13.000 So, we'll have an OSPF overview here. 00:00:13.000 --> 00:00:16.000 We'll look at our packets. We'll look at states. 00:00:16.000 --> 00:00:21.000 And we'll look at the design aspects of OSPF. 00:00:21.000 --> 00:00:23.000 So, what is OSPF? 00:00:23.000 --> 00:00:25.000 OSPF is Open Shortest Path First. 00:00:25.000 --> 00:00:28.000 It's an interior gateway routing protocol as we've discussed already. 00:00:28.000 --> 00:00:31.000 It's linked state routing protocol specifically developed by the ITF. 00:00:31.000 --> 00:00:33.000 So, we're dealing with an open standard. 00:00:33.000 --> 00:00:42.000 And the fundamental RFC version that we are dealing with on our Cisco devices for OSPF v2 is RFC 2328. 00:00:42.000 --> 00:00:46.000 V2 means IPv4. That's what it means. 00:00:46.000 --> 00:00:50.000 So, OSPF v2 is for IPv4 based on RFC 2328. 00:00:50.000 --> 00:00:55.000 If you want to read RFC 2328, you'll learn a lot of information. 00:00:55.000 --> 00:00:58.000 But you'll also probably fall asleep many times. 00:00:58.000 --> 00:01:01.000 So, if you have trouble falling asleep, maybe read that RFC. 00:01:01.000 --> 00:01:06.000 Current version for IPv6, we call OSPF v3. 00:01:06.000 --> 00:01:09.000 And that is based on RFC 2340. 00:01:09.000 --> 00:01:11.000 Now, those are not the only two versions of OSPF. 00:01:11.000 --> 00:01:16.000 There is a third version of OSPF called OSPF address families. 00:01:16.000 --> 00:01:20.000 Anybody using OSPF address families? 00:01:20.000 --> 00:01:21.000 Okay. 00:01:21.000 --> 00:01:27.000 So, we do cover OSPF address families in an RC, E-N-A-R-S-I. 00:01:27.000 --> 00:01:32.000 That is for the exam 300-410. 00:01:32.000 --> 00:01:38.000 So, if you want to learn about OSPF address families, we cover that in an RC. 00:01:38.000 --> 00:01:40.000 So, what is OSPF address families? 00:01:41.000 --> 00:01:49.000 It's about having one instance of OSPF running that handles both of these together. 00:01:49.000 --> 00:01:55.000 One instance of OSPF running that handles both of these together. 00:01:55.000 --> 00:02:06.000 And what it does is it basically incorporates IPv4 into OSPF v3. 00:02:07.000 --> 00:02:15.000 So, what you'll find is that when you start learning about OSPF address families in another course, in RC 300-410, 00:02:15.000 --> 00:02:23.000 you will be using commands like router OSPF v3 for address families, 00:02:23.000 --> 00:02:25.000 but it's not the same version as this one. 00:02:25.000 --> 00:02:27.000 It's a totally different version. 00:02:27.000 --> 00:02:32.000 Whereas this one is configured with like IPv6 router OSPF, okay, 00:02:32.000 --> 00:02:34.000 this one is configured with router OSPF v3. 00:02:35.000 --> 00:02:42.000 So, it's very, very, very frustrating when there's three different ways to do something, 00:02:42.000 --> 00:02:48.000 but I encourage everyone, if you are working with OSPF 00:02:48.000 --> 00:02:52.000 and you are building a new OSPF environment at any time, 00:02:52.000 --> 00:02:59.000 start looking into OSPF address families because it also improves performance. 00:02:59.000 --> 00:03:02.000 They've adjusted a lot of the LSAs. 00:03:02.000 --> 00:03:08.000 It is superior to using this version right here, v2. 00:03:08.000 --> 00:03:11.000 So, definitely something to look at. 00:03:11.000 --> 00:03:17.000 I hope down the road we can stop teaching these right here and we can just teach OSPF address families. 00:03:17.000 --> 00:03:19.000 It's the same thing with EIGRP. 00:03:19.000 --> 00:03:27.000 There's such a thing as EIGRP for IPv4, EIGRP for IPv6, and named EIGRP. 00:03:28.000 --> 00:03:33.000 And named EIGRP incorporates both v4 and v6 into one configuration, 00:03:33.000 --> 00:03:42.000 but they've also enhanced that version of EIGRP to be far superior to the classic EIGRP for v4 and v6. 00:03:42.000 --> 00:03:47.000 So, again, something we teach in an RC is called named EIGRP as well. 00:03:47.000 --> 00:03:51.000 So, if you are an EIGRP fan, something you might want to look into if you're not aware of it. 00:03:51.000 --> 00:03:55.000 It also helps you deal with an issue related to higher speed links. 00:03:55.000 --> 00:04:04.000 With EIGRP, higher speed links do not work properly with classic EIGRP for IPv4 and IPv6. 00:04:04.000 --> 00:04:09.000 You have to use named EIGRP if you have interfaces that I think are over 10 gigs. 00:04:09.000 --> 00:04:12.000 So, if you have an environment with more than 10 gig interfaces in them, 00:04:12.000 --> 00:04:18.000 you're probably not getting the results that you should be getting with your dynamic routing protocol. 00:04:19.000 --> 00:04:20.000 All right. 00:04:20.000 --> 00:04:25.000 So, now, as we mentioned a little bit earlier, Andrew, besides what I showed you about EIGRP 00:04:25.000 --> 00:04:29.000 and the stuff you are going to have to review for the exam, 00:04:29.000 --> 00:04:34.000 the exam objectives state that you only have to compare and contrast EIGRP. 00:04:34.000 --> 00:04:40.000 So, let's go to the exam objectives, and we'll pull those up. 00:04:40.000 --> 00:04:47.000 And just to show you that, no, EIGRP is not something that you are going to be spending time configuring verified. 00:04:47.000 --> 00:04:48.000 That's all in an RC. 00:04:48.000 --> 00:04:50.000 Again, I'm not happy with that. 00:04:50.000 --> 00:04:52.000 I never have been. 00:04:52.000 --> 00:05:02.000 I truly feel that EIGRP should have been covered here, but they never did it. 00:05:03.000 --> 00:05:25.000 So, if we go under infrastructure as an example, you'll see that it states you have to compare routing concepts. 00:05:25.000 --> 00:05:26.000 So, compare them. 00:05:26.000 --> 00:05:29.000 That's why I created that chart for you. 00:05:29.000 --> 00:05:32.000 That is why I created the chart for you. 00:05:38.000 --> 00:05:39.000 All right. 00:05:39.000 --> 00:05:43.000 To help you answer this. 00:05:43.000 --> 00:05:44.000 All right. 00:05:44.000 --> 00:05:51.000 Other than that, configuring even simple OSPF V2, V3 environments, and you know what? 00:05:51.000 --> 00:05:52.000 V3 is not even on it. 00:05:52.000 --> 00:05:53.000 It's not even on it. 00:05:53.000 --> 00:05:54.000 We're not going to go through it. 00:05:54.000 --> 00:05:57.000 If you want to learn about V3, take an RC. 00:05:57.000 --> 00:05:58.000 Yeah. 00:05:58.000 --> 00:05:59.000 All right. 00:05:59.000 --> 00:06:02.000 And then EEBGP only. 00:06:02.000 --> 00:06:09.000 So, and they're very, very, you know, accurate about that when it comes to the certification exam. 00:06:15.000 --> 00:06:17.000 My practice exam, how close is it to the real exam? 00:06:17.000 --> 00:06:25.000 Well, we do our best to, no, who, let me check that practice exam out just for a second. 00:06:26.000 --> 00:06:27.000 Yep. 00:06:27.000 --> 00:06:28.000 Okay. 00:06:28.000 --> 00:06:30.000 So, yeah, that practice exam is ours. 00:06:30.000 --> 00:06:43.000 So, what we've done is we've taken our experience and we have done everything we can to mimic as close as we can without breaking the nondisclosure agreement to help you prepare for the certification exam. 00:06:43.000 --> 00:06:45.000 So, how close is it to the real exam? 00:06:45.000 --> 00:06:55.000 Well, we're going to cover as many topics and concepts as we possibly can to get you ready for the certification exam as best we can to test you, but it's not going to be, it's not going to be close enough to get us in trouble. 00:06:55.000 --> 00:06:56.000 Let's put it that way. 00:06:56.000 --> 00:06:57.000 All right. 00:06:57.000 --> 00:07:01.000 We've got to be careful with the nondisclosure agreement when you're dealing with certifications exams. 00:07:01.000 --> 00:07:05.000 Certification exams are not going to be close enough to get you ready for the certification exam. 00:07:06.000 --> 00:07:11.000 So, yeah, we based it on our own experience and we updated it as often as we can as time goes on. 00:07:11.000 --> 00:07:16.000 So, the CCNA exam was quite a bit different than our own practice exam. 00:07:16.000 --> 00:07:17.000 Okay. 00:07:17.000 --> 00:07:22.000 Well, the thing is, is that we can't create similar questions, right? 00:07:23.000 --> 00:07:25.000 Because if we do, we're going to get in trouble for that. 00:07:25.000 --> 00:07:28.000 But what we can do is test you on the same topics and concepts. 00:07:28.000 --> 00:07:29.000 That's the key. 00:07:29.000 --> 00:07:32.000 The key is, do you understand the topics and concepts that we're trying to get at? 00:07:32.000 --> 00:07:33.000 Right. 00:07:33.000 --> 00:07:37.000 And then you have your labs, the practice of the labs, because we can't create a practice exam with simulations in it. 00:07:37.000 --> 00:07:40.000 So, those are going to be part of your lab experience and stuff like that. 00:07:41.000 --> 00:07:42.000 Yeah. 00:07:42.000 --> 00:07:44.000 You really have to study a lot. 00:07:44.000 --> 00:07:45.000 Absolutely. 00:07:47.000 --> 00:07:49.000 You got to know the information. 00:07:49.000 --> 00:07:55.000 These exams, Cisco has created in a way where you have to know the information, you have to have a good understanding. 00:07:55.000 --> 00:07:58.000 And so, you're going to have to study that very carefully. 00:07:58.000 --> 00:07:59.000 Yeah. 00:07:59.000 --> 00:08:01.000 You really have to study a lot. 00:08:01.000 --> 00:08:02.000 Absolutely. 00:08:03.000 --> 00:08:05.000 You got to know the information. 00:08:05.000 --> 00:08:12.000 These exams, Cisco has created in a way where you have to know the information, you have to play with them in the lab environment. 00:08:12.000 --> 00:08:15.000 And the practice exam is not about testing yourself. 00:08:15.000 --> 00:08:16.000 It's about studying. 00:08:16.000 --> 00:08:18.000 That's what the practice exams are about. 00:08:18.000 --> 00:08:20.000 Studying, studying, studying. 00:08:20.000 --> 00:08:22.000 For example, you can take a practice exam today and pass it. 00:08:22.000 --> 00:08:24.000 It doesn't mean you know what you need to know. 00:08:24.000 --> 00:08:25.000 You have to study. 00:08:25.000 --> 00:08:31.000 And you have to do it as many times as you can, review as much as you can, learn about why things are correct, why things are incorrect. 00:08:31.000 --> 00:08:32.000 That's how you're going to pass the exam. 00:08:34.000 --> 00:08:36.000 So, OSPF key feature, scalable. 00:08:40.000 --> 00:08:42.000 EIGRP, not as scalable. 00:08:42.000 --> 00:08:44.000 And you'll see that in that chart I gave you. 00:08:44.000 --> 00:08:45.000 Converges quickly. 00:08:45.000 --> 00:08:46.000 What does that mean? 00:08:46.000 --> 00:08:50.000 When a change happens in the environment, it can update pretty quickly. 00:08:51.000 --> 00:08:57.000 EIGRP is faster, though, because EIGRP can keep backup paths ready to go. 00:08:57.000 --> 00:09:07.000 So, if the primary path fails, it immediately installs the backup path, whereas OSPF has to calculate the paths any time convergence happens. 00:09:07.000 --> 00:09:12.000 So, OSPF might take three or four seconds to converge, whereas EIGRP can do it in microseconds. 00:09:14.000 --> 00:09:16.000 Supports variable length subnet masking. 00:09:16.000 --> 00:09:17.000 So, does EIGRP. 00:09:17.000 --> 00:09:24.000 That just means any subnet mask is supported, whereas something like RIP V1 only supports slash 8, slash 16, slash 24. 00:09:24.000 --> 00:09:26.000 It doesn't understand any other subnet mask. 00:09:26.000 --> 00:09:27.000 That's true. 00:09:27.000 --> 00:09:29.000 RIP V1 doesn't understand any other subnet mask. 00:09:29.000 --> 00:09:31.000 RIP V2 is VLSM. 00:09:31.000 --> 00:09:32.000 EIGRP is VLSM. 00:09:32.000 --> 00:09:33.000 OSPF is VLSM. 00:09:33.000 --> 00:09:34.000 ISIS is VLSM. 00:09:36.000 --> 00:09:42.000 ECMP, equal cost multipathing, means that we will load balance automatically on equal metric paths. 00:09:43.000 --> 00:09:52.000 EIGRP load balances automatically on equal metric paths, but you can also load balance on unequal metric paths with EIGRP. 00:09:52.000 --> 00:09:53.000 That's pretty cool. 00:09:54.000 --> 00:10:07.000 And one of the cool things about the unequal load balancing with EIGRP is that if you have the unequal paths, EIGRP and your router is going to make sure that you are not load balancing 50-50 on those paths, 00:10:07.000 --> 00:10:10.000 because if the paths are not equal, it doesn't make sense to do so. 00:10:11.000 --> 00:10:20.000 What it will do is it will look to see what is the difference between those two paths and send more traffic down the better path than the other path. 00:10:20.000 --> 00:10:23.000 So, that's something EIGRP can do, not OSPF. 00:10:26.000 --> 00:10:27.000 Independent transport. 00:10:27.000 --> 00:10:29.000 So, we are not relying on TCP. 00:10:29.000 --> 00:10:31.000 We are not relying on UDP. 00:10:31.000 --> 00:10:33.000 We are relying on ourself for transportation. 00:10:33.000 --> 00:10:36.000 We are protocol number 89. 00:10:36.000 --> 00:10:38.000 EIGRP is protocol number 88. 00:10:39.000 --> 00:10:42.000 We efficiently share updates. 00:10:43.000 --> 00:10:50.000 So, essentially, we will not exchange updates unless a change occurs or every 30 minutes. 00:10:50.000 --> 00:10:51.000 All right. 00:10:51.000 --> 00:10:57.000 So, every 30 minutes at a minimum, we are going to exchange all information with each other. 00:10:57.000 --> 00:10:59.000 So, that way, everybody is synchronized. 00:10:59.000 --> 00:11:00.000 More on that later. 00:11:00.000 --> 00:11:04.000 EIGRP, you will only share information if a change occurs. 00:11:04.000 --> 00:11:06.000 We have a very simple metric. 00:11:06.000 --> 00:11:07.000 We'll see it later. 00:11:07.000 --> 00:11:17.000 But it's just basically based on interface bandwidth being converted into a cost value, something like we saw with Spanning Tree Protocol, 00:11:17.000 --> 00:11:22.000 and then adding up the cost of all the links along the path to decide which way to go. 00:11:23.000 --> 00:11:26.000 Manual route summarization is the only thing that's supported. 00:11:26.000 --> 00:11:28.000 I'll teach you how to do that later on tomorrow. 00:11:28.000 --> 00:11:31.000 And then authentication, very, very important as well. 00:11:31.000 --> 00:11:36.000 So, with OSPF, first and foremost, we're going to have to discover our neighboring routers. 00:11:36.000 --> 00:11:37.000 So, what does that mean? 00:11:37.000 --> 00:11:40.000 It means we have to enable the routing process on our device. 00:11:40.000 --> 00:11:44.000 We have to enable our interfaces to be part of the routing process. 00:11:44.000 --> 00:11:53.000 And then, using the multicast address 224005, we will send out hello packets that are going to be used to discover neighboring routers. 00:11:53.000 --> 00:11:57.000 And so, if I'm speaking OSPF and you're speaking OSPF, 00:11:57.000 --> 00:12:00.000 then we are going to form a neighbor adjacency with each other. 00:12:00.000 --> 00:12:03.000 And then, once we form a neighbor adjacency with each other, 00:12:03.000 --> 00:12:08.000 we have the ability to exchange what are called LSAs, link state advertisements with OSPF. 00:12:08.000 --> 00:12:11.000 So, more on LSAs later on tomorrow. 00:12:11.000 --> 00:12:22.000 But what's important for you to realize is that LSAs are the nuggets of information that are necessary in order to successfully learn about everything that's happening in the environment. 00:12:23.000 --> 00:12:30.000 So, every router is going to have to generate these things called LSAs and share those LSAs with other routers in the environment. 00:12:30.000 --> 00:12:34.000 And we do this anytime a neighborship forms. 00:12:34.000 --> 00:12:37.000 We do this whenever a change occurs. 00:12:37.000 --> 00:12:41.000 And we do this every 30 minutes, even if no change has occurred. 00:12:41.000 --> 00:12:47.000 And the reason why is because we are trying to make sure that everybody has accurate information. 00:12:48.000 --> 00:12:53.000 We don't want to be without accurate information for more than 30 minutes in an OSPF routing domain. 00:12:53.000 --> 00:12:56.000 Typically, you shouldn't have inaccurate information. 00:12:56.000 --> 00:13:00.000 But if it does happen, everybody should be synchronized again within 30 minutes. 00:13:00.000 --> 00:13:05.000 If not, then the end result is that you have other problems on your hands that you're going to have to figure out and solve. 00:13:05.000 --> 00:13:12.000 Also, the reason why we have to update every 30 minutes is because every LSA has a maximum age of 60 minutes. 00:13:12.000 --> 00:13:15.000 LSAs have a maximum lifetime of 60 minutes. 00:13:15.000 --> 00:13:18.000 LSAs have a maximum lifetime of 60 minutes. 00:13:18.000 --> 00:13:20.000 One hour. 00:13:20.000 --> 00:13:23.000 So, that means I have to constantly at least once every hour. 00:13:23.000 --> 00:13:27.000 So, every 30 minutes essentially is what the paranoid update timer is called. 00:13:27.000 --> 00:13:34.000 But once every hour, at least, we're going to have to exchange those LSAs to make sure that we don't expire them. 00:13:34.000 --> 00:13:39.000 With OSPF, we maintain a complete view of our network. 00:13:39.000 --> 00:13:43.000 Well, that is true and not true at the exact same time. 00:13:43.000 --> 00:13:44.000 All right. 00:13:44.000 --> 00:13:46.000 That's not what I want. 00:13:53.000 --> 00:13:56.000 We go back to this image here. 00:13:56.000 --> 00:13:58.000 OSPF has a complete view. 00:13:58.000 --> 00:14:01.000 EIGRP would only know, oh, I can go that way or I can go that way. 00:14:01.000 --> 00:14:03.000 That's pretty much it. 00:14:03.000 --> 00:14:05.000 Whereas OSPF, it really knows about everything. 00:14:05.000 --> 00:14:13.000 But that is only true to a certain extent because you only have a map, an entire map of the area you're in. 00:14:13.000 --> 00:14:16.000 So, we're going to look at design here as well today. 00:14:16.000 --> 00:14:20.000 And we're going to see that with OSPF, we create multiple areas. 00:14:20.000 --> 00:14:25.000 And so, by creating multiple areas, right, we have maps for each and every single area. 00:14:25.000 --> 00:14:28.000 And the map only exists for that particular area. 00:14:28.000 --> 00:14:29.000 So, Area 0 would have a map. 00:14:29.000 --> 00:14:30.000 Area 51 would have a map. 00:14:30.000 --> 00:14:32.000 Area 1 would have a map. 00:14:32.000 --> 00:14:33.000 Area 8 would have a map. 00:14:33.000 --> 00:14:37.000 So, all of your different areas would have maps associated with them. 00:14:37.000 --> 00:14:42.000 So, when we say it maintains a complete view of the network, it's not the entire network unless you have just one area. 00:14:42.000 --> 00:14:48.000 If you're just using one giant area for OSPF, then, yes, you have a complete view of the entire network as a router. 00:14:48.000 --> 00:14:55.000 But if you are breaking up your network into multiple areas, then you really only have a complete view of your area that you are in. 00:14:55.000 --> 00:15:02.000 We use Dijkstra's, D-I-J-K, D-I-J-K-S-T-R-A, Dijkstra's. 00:15:02.000 --> 00:15:07.000 Dijkstra's shortest path first algorithm in order to make decisions. 00:15:07.000 --> 00:15:10.000 So, once we have our topological map with all the information in it, 00:15:10.000 --> 00:15:17.000 Dijkstra's shortest path first algorithm can be utilized to figure out what is the best way for us to go to reach our particular destination. 00:15:17.000 --> 00:15:21.000 And then the best choice is the one that's going to be installed on the routing table. 00:15:21.000 --> 00:15:25.000 Also, don't forget administrative distance has to come into play, all of that stuff as well. 00:15:25.000 --> 00:15:29.000 So, before we even start determining, hey, are we going to use this path or not, 00:15:29.000 --> 00:15:33.000 our router has to figure out, hey, what's the administrative distance? 00:15:33.000 --> 00:15:41.000 If it's 190, sorry, if it's 110, and we're also running EIGRP and we've learned the same network from EIGRP, 00:15:41.000 --> 00:15:48.000 well, then none of this stuff matters anymore because we're going to use EIGRP anyways. 00:15:48.000 --> 00:15:52.000 And cost is the name of our metric, as somebody chatted in a little bit earlier. 00:15:52.000 --> 00:15:57.000 All right, so OSPF packets. 00:15:57.000 --> 00:16:09.000 OSPF packets are going to be used to exchange things between our routers. 00:16:09.000 --> 00:16:14.000 We have five different packet types. 00:16:14.000 --> 00:16:21.000 The hello packet is used to discover and maintain our neighborhoods. 00:16:21.000 --> 00:16:32.000 This is the packet that we are going to send out of our interfaces at regular intervals on an ongoing basis. 00:16:32.000 --> 00:16:39.000 So, that way there, we can, one, establish that neighborhood agency, and then, two, keep it going, keep it maintained. 00:16:39.000 --> 00:16:46.000 And this is the one that uses 224005 automatically by default right out of the box. 00:16:46.000 --> 00:16:48.000 Keep that in mind. 00:16:48.000 --> 00:16:51.000 A lot of our other packets are going to use 224005 as well. 00:16:51.000 --> 00:16:57.000 But typically, when you're tested on the exam, 224005, hello packet, they typically go together, 00:16:57.000 --> 00:17:01.000 and more than likely that's the answer they're looking for. 00:17:01.000 --> 00:17:09.000 Once we have successfully identified each other and became neighbors with each other, 00:17:09.000 --> 00:17:14.000 what we have to do is we are going to have to exchange what are called the DVD packets. 00:17:14.000 --> 00:17:15.000 What is a DVD packet? 00:17:15.000 --> 00:17:18.000 It's a database descriptor packet. 00:17:18.000 --> 00:17:22.000 What this is is basically a summary of information. 00:17:22.000 --> 00:17:26.000 It's like your CliffsNotes or your ColesNotes, depending on where you are. 00:17:26.000 --> 00:17:27.000 What is that? 00:17:27.000 --> 00:17:34.000 Well, it's just a scaled-down version with just the most important information. 00:17:34.000 --> 00:17:37.000 So, the details are missing. 00:17:37.000 --> 00:17:44.000 So, with the DVD, what we have is we have what are called LSA headers. 00:17:44.000 --> 00:17:51.000 And the LSA headers are going to be exchanged between the two different routers. 00:17:51.000 --> 00:17:54.000 So, basically, you can think of it this way. 00:17:54.000 --> 00:17:59.000 I send you my LSA headers in a DVD packet. 00:17:59.000 --> 00:18:00.000 You send me yours. 00:18:00.000 --> 00:18:06.000 And essentially, the LSA headers say, I know about this, 10.0.0.0.24. 00:18:06.000 --> 00:18:08.000 I know about 10.0.1.0.24. 00:18:08.000 --> 00:18:09.000 I know about 10.0.2.0. 00:18:09.000 --> 00:18:10.000 I know about 10.0.2.0. 00:18:10.000 --> 00:18:11.000 Okay? 00:18:11.000 --> 00:18:12.000 That's it. 00:18:12.000 --> 00:18:13.000 That's it. 00:18:13.000 --> 00:18:15.000 There's no other details there. 00:18:15.000 --> 00:18:16.000 Why am I doing this? 00:18:16.000 --> 00:18:17.000 And why are we doing this? 00:18:17.000 --> 00:18:21.000 So, that way there, I can look at what you know. 00:18:21.000 --> 00:18:24.000 And I can compare that to what I already know. 00:18:24.000 --> 00:18:30.000 And if you have stuff I already know, then I'm not going to ask you for it. 00:18:30.000 --> 00:18:32.000 Because I already have it. 00:18:32.000 --> 00:18:38.000 See, in the world of OSPF, if I already have it, there's no need for you to tell me again. 00:18:38.000 --> 00:18:39.000 Okay? 00:18:39.000 --> 00:18:43.000 If I already have it, there's no need for you to tell me again. 00:18:43.000 --> 00:18:44.000 Why? 00:18:44.000 --> 00:18:48.000 Because you have the LSA that would have originated from the source. 00:18:48.000 --> 00:18:49.000 Right? 00:18:49.000 --> 00:18:54.000 And if I have it, I also have the LSA that originated from the source. 00:18:54.000 --> 00:19:00.000 So, we have the original LSA from the source that had been flooded through the environment. 00:19:00.000 --> 00:19:05.000 So, remember, we have a complete view of the topology because we learned directly from 00:19:05.000 --> 00:19:07.000 the sources in our area. 00:19:07.000 --> 00:19:10.000 So, if you know about it, you would have learned it from the source. 00:19:10.000 --> 00:19:14.000 If I know about it, I would have learned it from the source, meaning that I don't have 00:19:14.000 --> 00:19:15.000 to share it with you. 00:19:15.000 --> 00:19:16.000 We already know. 00:19:16.000 --> 00:19:22.000 So, what this does is it simplifies the exchange process by ensuring that we only exchange 00:19:22.000 --> 00:19:25.000 with each other those things that we don't know about. 00:19:25.000 --> 00:19:29.000 So, if I go down through that list, the DVD, and I notice that you know about 192.168.4.0, 00:19:29.000 --> 00:19:34.000 but I don't know about it, okay, then I know I'm going to have to ask you about that. 00:19:34.000 --> 00:19:36.000 Because I'm going to need the details from you. 00:19:36.000 --> 00:19:42.000 I'm going to need you to send me the actual LSA because I never learned about it for some 00:19:42.000 --> 00:19:43.000 reason. 00:19:43.000 --> 00:19:44.000 So, I want to get it from you. 00:19:44.000 --> 00:19:45.000 All right. 00:19:45.000 --> 00:19:47.000 So, that's why we have this DVD. 00:19:47.000 --> 00:19:48.000 All right. 00:19:48.000 --> 00:19:51.000 Now, when I want the 192.168.4.0, what I'm going to do, I'm going to send you that LSR, 00:19:51.000 --> 00:19:52.000 the link state request. 00:19:52.000 --> 00:19:57.000 So, the link state request is me asking you for something that I've identified in the 00:19:57.000 --> 00:20:00.000 DVD that I don't have, that you have. 00:20:00.000 --> 00:20:05.000 And then the LSU is you sending me the LSA. 00:20:05.000 --> 00:20:07.000 So, the LSU contains the LSA. 00:20:07.000 --> 00:20:10.000 Think of all these packets as envelopes. 00:20:10.000 --> 00:20:12.000 Think of them as all as envelopes. 00:20:12.000 --> 00:20:17.000 So, we have a hello envelope with information inside of it so we can discover and maintain 00:20:17.000 --> 00:20:18.000 neighborships. 00:20:18.000 --> 00:20:19.000 The DVD is an envelope. 00:20:19.000 --> 00:20:20.000 When you open it up, what does it have? 00:20:20.000 --> 00:20:21.000 It has LSA headers inside of it. 00:20:21.000 --> 00:20:25.000 The LSR would be an envelope, and inside of it I'd be like going, hey, can you send me 00:20:25.000 --> 00:20:28.000 the details for 192.168.4.0, size 24? 00:20:28.000 --> 00:20:32.000 And then the LSU is an envelope that contains LSAs. 00:20:32.000 --> 00:20:36.000 So, the link state advertisements, the actual details that are necessary. 00:20:36.000 --> 00:20:39.000 And we'll talk about LSAs a little later on. 00:20:39.000 --> 00:20:43.000 And then you have your LSAC, which is basically an empty envelope. 00:20:43.000 --> 00:20:46.000 So, if you send me a DVD, I got to acknowledge the fact that I received it. 00:20:46.000 --> 00:20:49.000 So, you send me a DVD, I send you an empty envelope basically. 00:20:49.000 --> 00:20:50.000 Thank you. 00:20:50.000 --> 00:20:51.000 All right. 00:20:51.000 --> 00:20:52.000 So, there you go. 00:20:52.000 --> 00:20:55.000 There's a rundown on these different packets, and they're going to come up again as we continue 00:20:55.000 --> 00:20:56.000 our discussion. 00:20:56.000 --> 00:20:59.000 So, when you think about a packet, what are we dealing with here? 00:20:59.000 --> 00:21:04.000 Well, we're dealing with OSPF that has an IPv4 or IPv6 header on it, depending on whether 00:21:04.000 --> 00:21:06.000 we're using OSPF v2 or v3. 00:21:06.000 --> 00:21:10.000 And then we have to wrap it in Ethernet framing information so that we can share it with each 00:21:10.000 --> 00:21:11.000 other. 00:21:11.000 --> 00:21:16.000 So, when you think about the IPv4, the source IP address would be the IP address of the 00:21:16.000 --> 00:21:17.000 interface. 00:21:17.000 --> 00:21:19.000 So, let's say it's going this way. 00:21:19.000 --> 00:21:24.000 So, this is the source IP of my interface. 00:21:24.000 --> 00:21:26.000 And what's the destination IP? 00:21:26.000 --> 00:21:30.000 The destination IP is going to be 224.0.0.5 as an example. 00:21:32.000 --> 00:21:33.000 And they would be in here. 00:21:38.000 --> 00:21:39.000 Right. 00:21:39.000 --> 00:21:42.000 Inside the OSPF packet, what's going to be there? 00:21:42.000 --> 00:21:44.000 Well, this is our header information here first. 00:21:45.000 --> 00:21:48.000 So, with our header information, we've got what? 00:21:48.000 --> 00:21:50.000 Version, type, packet length, router ID. 00:21:50.000 --> 00:21:54.000 So, we're going to talk about a lot of these more momentarily. 00:21:54.000 --> 00:21:58.000 But the router ID, area ID, checksums, authentication information, that's all in the header. 00:22:00.000 --> 00:22:01.000 And then you've got data. 00:22:02.000 --> 00:22:05.000 And so, if it's the hello packet, then we have hello specific data in there. 00:22:07.000 --> 00:22:10.000 If it's going to be the DVD packet, then it's what? 00:22:10.000 --> 00:22:13.000 It's the LSA header information that's going to be in the data part. 00:22:14.000 --> 00:22:15.000 If it's – what else do we have? 00:22:18.000 --> 00:22:19.000 The LSR. 00:22:19.000 --> 00:22:22.000 Then it's me requesting, hey, give me 192.168.4.0 LSA. 00:22:22.000 --> 00:22:27.000 If it's an LSU, then you're sending me the actual LSA for 192.168.4.0. 00:22:28.000 --> 00:22:33.000 And if it's an ACK, an LSACK, then that's just going to be empty, the data. 00:22:34.000 --> 00:22:35.000 So, that's how – that's what we're dealing with here. 00:22:36.000 --> 00:22:39.000 Version number would be like, is this version 4 versus version 6 as an example. 00:22:43.000 --> 00:22:45.000 Type, this is where it would reference. 00:22:45.000 --> 00:22:46.000 Is this type 1? 00:22:46.000 --> 00:22:47.000 Hello? 00:22:47.000 --> 00:22:48.000 Type 2? 00:22:48.000 --> 00:22:49.000 DVD? 00:22:49.000 --> 00:22:50.000 Type 3? 00:22:50.000 --> 00:22:51.000 LSR? 00:22:51.000 --> 00:22:52.000 Type 4? 00:22:52.000 --> 00:22:53.000 LSU? 00:22:53.000 --> 00:22:54.000 Type 5? 00:22:54.000 --> 00:22:55.000 LSACK? 00:22:55.000 --> 00:22:56.000 So, depending on the type up there determines what the data goes in there. 00:22:58.000 --> 00:22:59.000 Okay. 00:22:59.000 --> 00:23:04.000 So, these packets are going to be used at very specific states of the OSPF process. 00:23:05.000 --> 00:23:07.000 So, I have two routers here right now. 00:23:08.000 --> 00:23:10.000 I have this router and I have this router. 00:23:11.000 --> 00:23:12.000 And we have a link between them. 00:23:13.000 --> 00:23:16.000 So, first of all, you can only become neighbors with somebody if you're directly connected 00:23:16.000 --> 00:23:17.000 to them with OSPF. 00:23:18.000 --> 00:23:20.000 You cannot become neighbors with somebody if you're not directly connected to them. 00:23:21.000 --> 00:23:27.000 Now, directly connected is maybe not necessarily the best word because could I form an OSPF 00:23:27.000 --> 00:23:30.000 neighborhood with you over, let's say, a GRE tunnel? 00:23:30.000 --> 00:23:33.000 Yes, I could, but we are virtually directly connected to each other. 00:23:34.000 --> 00:23:37.000 Could I form an OSPF neighborhood with you over, let's say, DMVPN? 00:23:38.000 --> 00:23:40.000 Yes, I can, but again, we're virtually directly connected to each other. 00:23:42.000 --> 00:23:46.000 Could I form an OSPF neighborhood with you over an old-school, old-fashioned frame relay 00:23:46.000 --> 00:23:47.000 network? 00:23:47.000 --> 00:23:48.000 Anybody old enough to know what frame relay is? 00:23:49.000 --> 00:23:50.000 Okay. 00:23:50.000 --> 00:23:51.000 Yes, I can. 00:23:51.000 --> 00:23:52.000 Again, why? 00:23:52.000 --> 00:23:53.000 Because we're virtually directly connected to each other. 00:23:54.000 --> 00:23:58.000 Can we form an OSPF neighborhood over something like MPLS, Layer 2, VPN? 00:23:59.000 --> 00:24:00.000 Yes, we can. 00:24:00.000 --> 00:24:01.000 Why? 00:24:01.000 --> 00:24:03.000 Again, because we're virtually directly connected to each other in some way, shape, or form. 00:24:04.000 --> 00:24:06.000 So, again, it doesn't have to be physically directly connected. 00:24:07.000 --> 00:24:09.000 If we're virtually directly connected through a tunnel, we can form a neighborhood. 00:24:10.000 --> 00:24:14.000 But again, we are either physically or virtually directly connected to each other. 00:24:14.000 --> 00:24:17.000 That's the only way we can form OSPF neighborhood adjacencies. 00:24:18.000 --> 00:24:19.000 Why? 00:24:20.000 --> 00:24:27.000 It's because that multicast address we have, 224005, that is a non-routable multicast address. 00:24:28.000 --> 00:24:30.000 The other multicast address we'll talk about today is 224006. 00:24:31.000 --> 00:24:33.000 Again, that is a non-routable multicast address. 00:24:34.000 --> 00:24:40.000 So, if I send out this interface, the receiving device has to be in the same subnet slash 00:24:41.000 --> 00:24:42.000 VLAN slash broadcast domain as me. 00:24:42.000 --> 00:24:51.000 If not, then we can't form a neighborhood with each other because these are non-routable multicast addresses. 00:24:52.000 --> 00:24:55.000 So, we send out our hello packets. 00:24:56.000 --> 00:24:57.000 Send out my hello. 00:24:58.000 --> 00:25:01.000 You send out your hello. 00:25:02.000 --> 00:25:03.000 What does that mean? 00:25:04.000 --> 00:25:05.000 It means we're both in the downstate. 00:25:06.000 --> 00:25:11.000 So, my interface will be known as downstate for OSPF. 00:25:12.000 --> 00:25:15.000 That means I've sent hellos, but I haven't received any hellos yet. 00:25:16.000 --> 00:25:22.000 So, as soon as we receive the hello, that means we can then go to the init state, I-N-I-T. 00:25:23.000 --> 00:25:31.000 So, once I receive a hello and I've sent a hello, if you've sent a hello and received a hello, you can now go to the init state. 00:25:32.000 --> 00:25:33.000 So, in the init state, that's all it simply means. 00:25:34.000 --> 00:25:40.000 It means that you have successfully received a hello from a neighboring device and you have successfully been sending hellos. 00:25:41.000 --> 00:25:54.000 But, you have not confirmed yet if you are actually neighbors with each other that have bi-directional communication. 00:25:55.000 --> 00:25:57.000 Our goal is to get to the two-way state. 00:25:58.000 --> 00:25:59.000 This means we're neighbors. 00:26:00.000 --> 00:26:01.000 This means we have bi-directional communication. 00:26:02.000 --> 00:26:09.000 How do I know that you're my neighbor and how do you know that I'm your neighbor? 00:26:10.000 --> 00:26:13.000 Well, let's just take a quick peek at the hello packet right now. 00:26:14.000 --> 00:26:16.000 So, here's a quick peek at our hello packet. 00:26:17.000 --> 00:26:20.000 Notice in the hello packet, in the data field, we have neighbors. 00:26:21.000 --> 00:26:27.000 So, hello packet, data field, we have a neighbors field in that hello packet. 00:26:28.000 --> 00:26:30.000 What shows up in that neighbors field? 00:26:31.000 --> 00:26:35.000 The router IDs of your neighbors. 00:26:36.000 --> 00:26:39.000 The router IDs of your neighbors. 00:26:40.000 --> 00:26:46.000 So, if we go back to this page here, let's say this is the router ID for this router and this is the router ID for this router. 00:26:47.000 --> 00:26:50.000 So, I received a hello packet from you. 00:26:51.000 --> 00:26:54.000 So, I know that you are 0002. 00:26:55.000 --> 00:26:56.000 I know that. 00:26:57.000 --> 00:27:05.000 What I can do now is when I send the next hello packet, in that neighbor field, I'm going to put 0002. 00:27:06.000 --> 00:27:10.000 So, that way there, when you get it, you now confirm. 00:27:11.000 --> 00:27:19.000 I just received a hello packet from 0001 and in the neighbor field, I see my own router ID in the neighbor field. 00:27:20.000 --> 00:27:21.000 What does that mean? 00:27:21.000 --> 00:27:25.000 It means I know that you see me. 00:27:26.000 --> 00:27:27.000 Now, I'm two-way. 00:27:28.000 --> 00:27:29.000 So, likewise, this router would do the same. 00:27:30.000 --> 00:27:34.000 When it sends a hello packet in the neighbor field, it would put 0001. 00:27:35.000 --> 00:27:36.000 The router ID over here. 00:27:37.000 --> 00:27:46.000 So, now when it arrives, I know that I just received a hello packet from 0002 and they see me because in the neighbor field, it says 0001. 00:27:47.000 --> 00:27:49.000 So, now I know that you see me, I see you. 00:27:49.000 --> 00:27:50.000 We see each other. 00:27:51.000 --> 00:27:55.000 I see you, you see me, we're now neighbors happily, whatever. 00:27:56.000 --> 00:27:57.000 So, two-way state. 00:27:58.000 --> 00:27:59.000 Did I wake you up? 00:28:00.000 --> 00:28:06.000 We've got bi-directional communication now. 00:28:08.000 --> 00:28:09.000 That's what that means. 00:28:10.000 --> 00:28:17.000 So, the whole goal of this hello packet is just to simply get us from down ENIT to two-way, bi-directional communication. 00:28:17.000 --> 00:28:25.000 So, let's pause for a moment and look at that hello packet in a little bit more detail. 00:28:26.000 --> 00:28:31.000 And let's identify things that we really need to be aware of for the certification exam in case it shows up. 00:28:32.000 --> 00:28:38.000 So, first of all, things that are not even on this list that I want to bring up. 00:28:39.000 --> 00:28:43.000 Let's focus on this router forming a neighborhood with this router. 00:28:44.000 --> 00:28:52.000 First and foremost, must be in same subnet. 00:28:53.000 --> 00:28:54.000 That's a must. 00:28:55.000 --> 00:29:01.000 If you are not in the same subnet, you are not allowed to form neighbor adjacencies with each other. 00:29:02.000 --> 00:29:03.000 So, what does that mean? 00:29:03.000 --> 00:29:04.000 So, what does that mean? 00:29:04.000 --> 00:29:15.000 It means on the exam, if you are troubleshooting an OSPF configuration, take a look to make sure that those interfaces are in the exact same subnet. 00:29:16.000 --> 00:29:21.000 Meaning, look at their IP addresses, look at their subnet masks, and determine, are they actually truly in the same subnet? 00:29:22.000 --> 00:29:24.000 Those two interfaces that are trying to form a neighbor adjacency. 00:29:25.000 --> 00:29:26.000 If not, there's your problem. 00:29:26.000 --> 00:29:28.000 So, change the subnet mask to what it needs to be. 00:29:29.000 --> 00:29:30.000 Or change the IP to what it needs to be. 00:29:31.000 --> 00:29:32.000 And problem solved. 00:29:39.000 --> 00:29:41.000 MTUs of interfaces must match. 00:29:47.000 --> 00:29:48.000 By default. 00:29:48.000 --> 00:29:52.000 So, the MTU of this interface must match the MTU of this interface. 00:29:52.000 --> 00:29:54.000 Must match the MTU of this interface. 00:29:55.000 --> 00:29:56.000 Or we can't form a neighbor adjacency. 00:29:57.000 --> 00:29:58.000 What's the default MTU? 00:29:58.000 --> 00:29:59.000 It's 1500. 00:30:04.000 --> 00:30:07.000 However, you can override this behavior. 00:30:08.000 --> 00:30:09.000 That's right. 00:30:09.000 --> 00:30:10.000 You can override this behavior. 00:30:11.000 --> 00:30:12.000 Just so you know. 00:30:12.000 --> 00:30:13.000 If you didn't know. 00:30:14.000 --> 00:30:19.000 You can go to the interface that you are configuring for OSPF. 00:30:21.000 --> 00:30:23.000 So, for example, if we go to router number two. 00:30:25.000 --> 00:30:26.000 And we type in configure terminal. 00:30:28.000 --> 00:30:29.000 Interface. 00:30:30.000 --> 00:30:31.000 Fast Ethernet 0 slash 1 slash 0. 00:30:32.000 --> 00:30:33.000 And we type in. 00:30:34.000 --> 00:30:35.000 IP OSPF. 00:30:36.000 --> 00:30:37.000 MTU. 00:30:37.000 --> 00:30:38.000 Ignore. 00:30:38.000 --> 00:30:40.000 You actually should be able to see that. 00:30:40.000 --> 00:30:41.000 IP OSPF. 00:30:41.000 --> 00:30:42.000 MTU. 00:30:42.000 --> 00:30:43.000 Ignore. 00:30:43.000 --> 00:30:44.000 You actually shut off that check. 00:30:45.000 --> 00:30:46.000 You actually shut it off. 00:30:47.000 --> 00:30:48.000 You can shut it off if you want to. 00:30:49.000 --> 00:30:50.000 It's not recommended you do so. 00:30:50.000 --> 00:30:51.000 But you can. 00:30:52.000 --> 00:30:55.000 Which means that then the MTU does not have to match at all. 00:30:57.000 --> 00:30:58.000 So, just something to be aware of for the real world. 00:31:11.000 --> 00:31:12.000 Router IDs. 00:31:13.000 --> 00:31:14.000 Must. 00:31:15.000 --> 00:31:16.000 Be. 00:31:16.000 --> 00:31:17.000 Unique. 00:31:20.000 --> 00:31:21.000 Look, two routers have the same router ID. 00:31:22.000 --> 00:31:24.000 They will not form an OSPF neighbor adjacency with each other. 00:31:29.000 --> 00:31:30.000 Why? 00:31:30.000 --> 00:31:31.000 Because the OSPF router ID and OSPF neighbor adjacency are not the same. 00:31:33.000 --> 00:31:34.000 Okay? 00:31:35.000 --> 00:31:36.000 So, that's something to be aware of. 00:31:37.000 --> 00:31:38.000 Why? 00:31:38.000 --> 00:31:39.000 Because the router ID and OSPF is a unique identifier identifying that router amongst all the other routers participating in OSPF. 00:31:50.000 --> 00:31:51.000 And everything that you send out in that OSPF environment, like when you send out an LSA, you are going to label it with your router ID. 00:31:58.000 --> 00:31:59.000 You send out a VBD, you're labeling it with your router ID. 00:32:02.000 --> 00:32:03.000 As you can see, the router ID is going to show up in the packet. 00:32:04.000 --> 00:32:05.000 It's going to show up in the packet. 00:32:05.000 --> 00:32:06.000 So, it doesn't matter if it's a Hello, a DBD, an LSR, an LSU, an LSAC, the router ID shows up. 00:32:13.000 --> 00:32:14.000 So, if I send a packet out with my router ID and you send out with your router ID and they're the exact same router IDs, then that's a conflict. 00:32:21.000 --> 00:32:22.000 We can't have that. 00:32:22.000 --> 00:32:23.000 Because then we are not unique. 00:32:25.000 --> 00:32:26.000 Now, you might be saying, well, what if this router, Raymond, has the router ID 0001 and I have the router ID 0001. 00:32:34.000 --> 00:32:35.000 Well, that has nothing to do with neighbor adjacencies. 00:32:39.000 --> 00:32:40.000 Will that cause a problem? 00:32:40.000 --> 00:32:41.000 Yes, that will absolutely cause a problem. 00:32:45.000 --> 00:32:46.000 Two routers with the same router ID in your environment will cause an LSA flood war. 00:32:55.000 --> 00:32:56.000 That's what's going to be caused if you have two routers with the same router ID. 00:32:59.000 --> 00:33:00.000 Now, what is an LSA flood war? 00:33:00.000 --> 00:33:01.000 An LSA flood war happens when this router ID is the same as the other. 00:33:04.000 --> 00:33:05.000 So, this router sends out its LSA saying, hey, I'm 0001 and these are all the networks that are directly connected to me that are participating OSPF on me. 00:33:13.000 --> 00:33:14.000 And it goes out, this router gets it, does what it needs to do with it, copies it, sends it on its particular way. 00:33:20.000 --> 00:33:21.000 Eventually, this router gets it. 00:33:21.000 --> 00:33:22.000 And don't forget, every other router is going to get it as well. 00:33:24.000 --> 00:33:25.000 And so, this router gets it and goes, oh, I just received something from 001. 00:33:31.000 --> 00:33:32.000 That's me. 00:33:32.000 --> 00:33:33.000 And then it looks through it and goes, that's not my information. 00:33:36.000 --> 00:33:37.000 What happened to this thing? 00:33:38.000 --> 00:33:39.000 All right, I might as well create a new one. 00:33:40.000 --> 00:33:41.000 So, it creates a new LSA, labels it 0001, and then puts all the details in it about itself and everything else that goes along with it and sends it out on the network. 00:33:49.000 --> 00:33:50.000 Everybody's updating themselves. 00:33:51.000 --> 00:33:52.000 Eventually, this router gets it. 00:33:52.000 --> 00:33:53.000 This router looks at it and goes, 0001. 00:34:02.000 --> 00:34:03.000 That doesn't make any sense. 00:34:04.000 --> 00:34:05.000 That's not me. 00:34:06.000 --> 00:34:07.000 Right? 00:34:15.000 --> 00:34:16.000 And that has nothing to do with R2 or anything like that. 00:34:18.000 --> 00:34:19.000 Don't worry about the area numbers in this particular case. 00:34:20.000 --> 00:34:21.000 It has everything to do with the fact that we have two routers with the same router ID. 00:34:24.000 --> 00:34:25.000 So, if they're in the same area, we'd have the problem. 00:34:26.000 --> 00:34:27.000 If they're in different areas, the area border router would actually have a problem. 00:34:29.000 --> 00:34:30.000 So, yeah, the problem is that we have two routers with the same router ID. 00:34:32.000 --> 00:34:33.000 The problem is variable depending on where the two routers are. 00:34:35.000 --> 00:34:36.000 But in the end, we ultimately end up with routers that are tossing out information over and over and over and over again to try and solve this problem that exists. 00:34:45.000 --> 00:34:46.000 So, that's what your flood war is. 00:34:48.000 --> 00:34:49.000 All right, so router IDs, just remember, must be unique. 00:34:52.000 --> 00:34:53.000 Area ID. 00:34:53.000 --> 00:34:54.000 Okay, what is the area ID? 00:34:55.000 --> 00:34:56.000 It's the area you belong to. 00:34:57.000 --> 00:34:58.000 So, you'll see here that R1 belongs to area 0 in this diagram. 00:35:00.000 --> 00:35:01.000 Okay, well, no. 00:35:01.000 --> 00:35:02.000 R1 does not belong to area 0. 00:35:03.000 --> 00:35:04.000 Let's be clear about that. 00:35:05.000 --> 00:35:06.000 Yeah, you have to be careful with OSPF. 00:35:08.000 --> 00:35:09.000 Your entire router is not part of an area. 00:35:11.000 --> 00:35:12.000 Your interfaces are part of areas. 00:35:14.000 --> 00:35:15.000 Notice that this is an area 0. 00:35:16.000 --> 00:35:17.000 This is an area 0. 00:35:18.000 --> 00:35:19.000 This is not. 00:35:20.000 --> 00:35:21.000 It's a big difference there. 00:35:21.000 --> 00:35:22.000 Look at R2. 00:35:22.000 --> 00:35:23.000 This is an area 0. 00:35:24.000 --> 00:35:25.000 This is an area 0. 00:35:26.000 --> 00:35:27.000 This is an area 1. 00:35:29.000 --> 00:35:30.000 So, it's not your router that belongs to area 0. 00:35:31.000 --> 00:35:32.000 It's not your router that's in an area. 00:35:33.000 --> 00:35:34.000 It's your interfaces that are in areas. 00:35:36.000 --> 00:35:37.000 So, when we say area ID must match, 00:35:41.000 --> 00:35:42.000 we are talking about the fact that 00:35:43.000 --> 00:35:44.000 when you're trying to form a neighborhood with somebody, 00:35:46.000 --> 00:35:47.000 that neighbor must be in the same area as you. 00:35:51.000 --> 00:35:52.000 The neighbor must be in the same area as that interface. 00:36:02.000 --> 00:36:03.000 So, if I did this, that's a problem. 00:36:07.000 --> 00:36:08.000 That's a problem. 00:36:10.000 --> 00:36:11.000 So, it's very important for you to recognize that 00:36:12.000 --> 00:36:13.000 on an exam, when they draw lines through the router, 00:36:16.000 --> 00:36:17.000 like this, that's on purpose. 00:36:18.000 --> 00:36:19.000 You need to recognize that, oh, those are in area 0. 00:36:21.000 --> 00:36:22.000 That's not even part of OSPF. 00:36:23.000 --> 00:36:24.000 That's not even running OSPF, that interface. 00:36:25.000 --> 00:36:26.000 Those two are area 0. 00:36:27.000 --> 00:36:28.000 That one's area 1. 00:36:29.000 --> 00:36:30.000 Those two are not part of OSPF. 00:36:31.000 --> 00:36:32.000 They're going to be very deliberate about that. 00:36:35.000 --> 00:36:36.000 And if they're not, shame on them for doing that. 00:36:38.000 --> 00:36:39.000 It means a person who created the diagram 00:36:40.000 --> 00:36:41.000 doesn't know what they're doing. 00:36:44.000 --> 00:36:45.000 As you can see, pretty passionate 00:36:46.000 --> 00:36:47.000 about proper diagrams for an exam. 00:36:56.000 --> 00:36:57.000 And so, when we go to our configuration layer, 00:36:58.000 --> 00:36:59.000 you're going to see this. 00:36:59.000 --> 00:37:00.000 You're going to see this in action. 00:37:01.000 --> 00:37:02.000 I have taken over 130 certification exams to date. 00:37:08.000 --> 00:37:09.000 And when I see poorly drawn diagrams on an exam, 00:37:12.000 --> 00:37:13.000 as an instructor, it frustrates me 00:37:14.000 --> 00:37:15.000 because then I know when my fellow students 00:37:17.000 --> 00:37:18.000 go and take the exam, 00:37:19.000 --> 00:37:20.000 they're going to experience that bad diagram 00:37:21.000 --> 00:37:22.000 and that's not fair. 00:37:23.000 --> 00:37:24.000 That's not fair for anybody to have to go through that. 00:37:32.000 --> 00:37:33.000 Right. 00:37:34.000 --> 00:37:35.000 So, what else? 00:37:36.000 --> 00:37:37.000 We got must be in the same subnet. 00:37:38.000 --> 00:37:39.000 MTUs must match. 00:37:40.000 --> 00:37:41.000 You know, folks, we're taking our time here 00:37:42.000 --> 00:37:43.000 because this is critical for your exam success. 00:37:44.000 --> 00:37:45.000 You'll never know when you'll get a question or two 00:37:46.000 --> 00:37:47.000 that just throws stuff like this at you 00:37:48.000 --> 00:37:49.000 and you're like, ah, you got to know. 00:37:50.000 --> 00:37:51.000 You got to know. 00:37:51.000 --> 00:37:52.000 Okay, authentication must match. 00:37:53.000 --> 00:37:54.000 So, authentication information's in your header. 00:37:55.000 --> 00:37:56.000 What does that mean? 00:37:57.000 --> 00:37:58.000 Well, authentication, again, 00:37:59.000 --> 00:38:00.000 not on a router-by-router basis. 00:38:01.000 --> 00:38:02.000 It has to be identically. 00:38:03.000 --> 00:38:04.000 So, if I have this interface participating in OSPF 00:38:05.000 --> 00:38:06.000 and I have authentication for OSPF, 00:38:07.000 --> 00:38:08.000 then I have to have 00:38:09.000 --> 00:38:10.000 the same authentication parameters over here. 00:38:11.000 --> 00:38:12.000 It's pretty obvious, right? 00:38:13.000 --> 00:38:14.000 That is pretty obvious that it has to be the same. 00:38:15.000 --> 00:38:16.000 Okay, but that means I could have 00:38:17.000 --> 00:38:18.000 different authentication parameters somewhere else. 00:38:19.000 --> 00:38:20.000 So, for example, this interface 00:38:21.000 --> 00:38:22.000 could use different authentication parameters 00:38:23.000 --> 00:38:24.000 as long as the router on the other side 00:38:25.000 --> 00:38:26.000 is using the same authentication parameters over there. 00:38:27.000 --> 00:38:28.000 So, as you can see, 00:38:29.000 --> 00:38:30.000 a lot of the stuff we're going to be doing 00:38:31.000 --> 00:38:32.000 is on an interface-by-interface basis 00:38:33.000 --> 00:38:34.000 with OSPF, 00:38:35.000 --> 00:38:36.000 not a router-by-router basis. 00:38:37.000 --> 00:38:38.000 It's always interface-by-interface basis 00:38:39.000 --> 00:38:42.000 with OSPF. 00:38:43.000 --> 00:38:44.000 There are a few features, though, 00:38:45.000 --> 00:38:46.000 that you can enable for the entire router, 00:38:47.000 --> 00:38:48.000 but even though you may think 00:38:49.000 --> 00:38:50.000 it's for the entire router, 00:38:51.000 --> 00:38:52.000 by the time you're finished configuring it, 00:38:53.000 --> 00:38:54.000 it's really only affecting certain interfaces 00:38:55.000 --> 00:38:59.000 that are part of OSPF. 00:38:59.000 --> 00:39:00.000 Hello and dead interval. 00:39:01.000 --> 00:39:02.000 Why in the world 00:39:03.000 --> 00:39:04.000 would OSPF 00:39:05.000 --> 00:39:06.000 carry 00:39:07.000 --> 00:39:09.000 the hello and dead interval numbers 00:39:10.000 --> 00:39:11.000 in the data field? 00:39:12.000 --> 00:39:13.000 Think about that for a second. 00:39:14.000 --> 00:39:15.000 Why in the world 00:39:16.000 --> 00:39:17.000 would OSPF carry 00:39:18.000 --> 00:39:19.000 the numbers that it's using? 00:39:20.000 --> 00:39:21.000 For example, 00:39:22.000 --> 00:39:23.000 this router 00:39:24.000 --> 00:39:25.000 sends a hello, 00:39:26.000 --> 00:39:27.000 and it says, 00:39:27.000 --> 00:39:28.000 hello is 10, 00:39:29.000 --> 00:39:30.000 and my dead is 4 times the hello, 00:39:31.000 --> 00:39:32.000 which would equal 40. 00:39:33.000 --> 00:39:34.000 Yes, 00:39:34.000 --> 00:39:35.000 if you're ever asked on an exam, 00:39:36.000 --> 00:39:37.000 what is the dead interval? 00:39:38.000 --> 00:39:39.000 The answer is 4 times the hello. 00:39:40.000 --> 00:39:41.000 If you see 4 times the hello 00:39:42.000 --> 00:39:43.000 in the answer options, 00:39:44.000 --> 00:39:45.000 that's the one you pick. 00:39:46.000 --> 00:39:47.000 4 times the hello. 00:39:48.000 --> 00:39:49.000 Why? 00:39:50.000 --> 00:39:51.000 Because if I change this to 11, 00:39:52.000 --> 00:39:53.000 this automatically becomes 44. 00:39:54.000 --> 00:39:55.000 If I change this to 12, 00:39:55.000 --> 00:39:56.000 this automatically becomes 12. 00:39:57.000 --> 00:39:58.000 Why do they carry it? 00:39:59.000 --> 00:40:00.000 Because the hello and dead intervals 00:40:01.000 --> 00:40:02.000 between neighbors 00:40:03.000 --> 00:40:04.000 must match. 00:40:05.000 --> 00:40:06.000 The hello and dead intervals 00:40:07.000 --> 00:40:09.000 are an interface configuration. 00:40:10.000 --> 00:40:11.000 If we go to our router right now, 00:40:12.000 --> 00:40:13.000 R2 in our live environment, 00:40:14.000 --> 00:40:15.000 and we type in something like, 00:40:16.000 --> 00:40:17.000 let's just type in do, show, run, 00:40:18.000 --> 00:40:19.000 interface, 00:40:20.000 --> 00:40:21.000 whatever, 00:40:22.000 --> 00:40:23.000 fastethernet0 slash 1 slash 0. 00:40:23.000 --> 00:40:24.000 You'll see I'm participating 00:40:25.000 --> 00:40:26.000 in OSPF area 0 00:40:27.000 --> 00:40:28.000 in this case, 00:40:29.000 --> 00:40:30.000 but we will change that later. 00:40:31.000 --> 00:40:32.000 We will change that later. 00:40:33.000 --> 00:40:34.000 This doesn't match my diagram right now. 00:40:35.000 --> 00:40:36.000 We're going to build this tomorrow. 00:40:37.000 --> 00:40:38.000 What I want to show you is 00:40:39.000 --> 00:40:40.000 if we type in IP OSPF hello interval, 00:40:41.000 --> 00:40:42.000 notice that I got 1 to 65,535 seconds. 00:40:43.000 --> 00:40:44.000 We said the default is 10, 00:40:45.000 --> 00:40:46.000 and we said it must match. 00:40:47.000 --> 00:40:48.000 What I'm going to do is 00:40:49.000 --> 00:40:50.000 I'm going to change it to 12 right now. 00:40:51.000 --> 00:40:52.000 I've changed it to 12, 00:40:54.000 --> 00:40:55.000 but what I want to point out to you 00:40:56.000 --> 00:40:57.000 is the router on this side 00:40:58.000 --> 00:40:59.000 is still using 10, 00:41:00.000 --> 00:41:01.000 still using 10. 00:41:02.000 --> 00:41:03.000 When our dead timer expires here, 00:41:04.000 --> 00:41:05.000 and we start trying 00:41:06.000 --> 00:41:07.000 to reestablish our neighborhood, 00:41:08.000 --> 00:41:09.000 it's not going to work 00:41:10.000 --> 00:41:11.000 because our timers do not match. 00:41:12.000 --> 00:41:14.000 Our timers do not match. 00:41:15.000 --> 00:41:16.000 We have a timer mismatch. 00:41:17.000 --> 00:41:18.000 Timers must match. 00:41:19.000 --> 00:41:20.000 That is the rule. 00:41:21.000 --> 00:41:22.000 Now, again, since it's an interface command, 00:41:23.000 --> 00:41:24.000 could I have different timers 00:41:25.000 --> 00:41:26.000 on all three of these interfaces? 00:41:27.000 --> 00:41:29.000 Yes, of course you can. 00:41:30.000 --> 00:41:31.000 You can have different timers 00:41:32.000 --> 00:41:33.000 on all three of these interfaces. 00:41:34.000 --> 00:41:35.000 What matters is that the timers 00:41:36.000 --> 00:41:37.000 for the neighbor interfaces match. 00:41:38.000 --> 00:41:39.000 As you can see now, 00:41:40.000 --> 00:41:41.000 our dead timer has expired, 00:41:42.000 --> 00:41:43.000 and we have not formed 00:41:44.000 --> 00:41:45.000 another neighbor adjacency. 00:41:46.000 --> 00:41:47.000 If I type in do show IP OSPF neighbors, 00:41:48.000 --> 00:41:50.000 I don't have a neighborship right now 00:41:51.000 --> 00:41:52.000 out that interface 00:41:53.000 --> 00:41:54.000 0-1-0. 00:41:55.000 --> 00:41:56.000 Why the timers do not match. 00:42:05.000 --> 00:42:06.000 Set it back to 10, 00:42:07.000 --> 00:42:08.000 and you'll see now that the timers match, 00:42:09.000 --> 00:42:10.000 we form a neighbor adjacency. 00:42:13.000 --> 00:42:15.000 Little things to keep in mind for the exam. 00:42:16.000 --> 00:42:17.000 You might be showing output like that, 00:42:18.000 --> 00:42:19.000 and it says troubleshoot this, 00:42:20.000 --> 00:42:21.000 troubleshoot that. 00:42:21.000 --> 00:42:22.000 Why is the OSPF not working? 00:42:23.000 --> 00:42:24.000 Why this? Why that? 00:42:25.000 --> 00:42:26.000 These are all things that you must be able to check. 00:42:27.000 --> 00:42:28.000 Later on, when we do configuration 00:42:29.000 --> 00:42:30.000 and verification tomorrow, 00:42:31.000 --> 00:42:32.000 we're going to be going through various output 00:42:33.000 --> 00:42:34.000 and trying to say here's your timer, 00:42:35.000 --> 00:42:36.000 here's this, here's that, here's this, here's that. 00:42:37.000 --> 00:42:38.000 That'll be places where you can go 00:42:39.000 --> 00:42:40.000 and verify this stuff. 00:42:45.000 --> 00:42:46.000 This we've already covered, 00:42:47.000 --> 00:42:48.000 but as we said, 00:42:49.000 --> 00:42:50.000 as we're exchanging our hello packets, 00:42:51.000 --> 00:42:52.000 I know who you are 00:42:53.000 --> 00:42:54.000 because your router ID is in your hello packet. 00:42:55.000 --> 00:42:56.000 You send me a hello packet, 00:42:57.000 --> 00:42:59.000 I now know you are, let's say, 0-0-0-2. 00:43:00.000 --> 00:43:01.000 When I send you a hello packet, 00:43:02.000 --> 00:43:03.000 the router ID, 00:43:04.000 --> 00:43:05.000 let's say this is 0-0-0-5, 00:43:06.000 --> 00:43:07.000 then I would put 0-0-0-5 in here 00:43:08.000 --> 00:43:09.000 because it's my packet, 00:43:10.000 --> 00:43:11.000 but in the data, in the neighbor field, 00:43:12.000 --> 00:43:13.000 I put 0-0-0-2. 00:43:14.000 --> 00:43:15.000 That way there, when you receive it, 00:43:16.000 --> 00:43:17.000 you know it's for me, 00:43:18.000 --> 00:43:19.000 and you know I see you. 00:43:20.000 --> 00:43:21.000 You now know I see you, 00:43:22.000 --> 00:43:23.000 and that's how we're going to get down 00:43:24.000 --> 00:43:25.000 to the two-way state that I talked about earlier. 00:43:30.000 --> 00:43:33.000 This here is all about the DR-BDR election process, 00:43:34.000 --> 00:43:36.000 so we're going to save that for discussion later. 00:43:37.000 --> 00:43:38.000 I don't want to talk about it right now, 00:43:39.000 --> 00:43:42.000 but this here is very critical, 00:43:43.000 --> 00:43:45.000 the DR-BDR process for your certification exam. 00:43:46.000 --> 00:43:47.000 Always, you're guaranteed 00:43:47.000 --> 00:43:48.000 to at least get one question on it. 00:43:49.000 --> 00:43:50.000 Whether it is technically accurate or not, 00:43:51.000 --> 00:43:52.000 it doesn't matter. 00:43:52.000 --> 00:43:53.000 You're guaranteed to get one question on it on the exam. 00:43:54.000 --> 00:43:55.000 Another one of my pet peeves of Cisco exams 00:43:56.000 --> 00:43:57.000 when it comes to that. 00:43:58.000 --> 00:43:59.000 Anyways, we'll talk about that when we get to that tomorrow. 00:44:00.000 --> 00:44:01.000 This is not something we're going to do 00:44:02.000 --> 00:44:03.000 or configure here in Encore. 00:44:04.000 --> 00:44:05.000 This is something you're going to configure in an RC 00:44:06.000 --> 00:44:07.000 if you get that far in advanced routing, 00:44:08.000 --> 00:44:11.000 the 300-410 certification exam. 00:44:12.000 --> 00:44:14.000 The stub area flag is utilized 00:44:15.000 --> 00:44:18.000 when you have a stub area, 00:44:19.000 --> 00:44:23.000 a totally stubby area, 00:44:25.000 --> 00:44:27.000 a not-so-stubby area, 00:44:28.000 --> 00:44:30.000 and a totally not-so-stubby area. 00:44:33.000 --> 00:44:34.000 I didn't make up those terms. 00:44:35.000 --> 00:44:37.000 But what does it allow you to do? 00:44:38.000 --> 00:44:41.000 It allows you to change the behavior of the area. 00:44:42.000 --> 00:44:47.000 If I turn this area into a not-so-stubby area, 00:44:50.000 --> 00:44:52.000 then I would have to make sure I tell this router that, 00:44:53.000 --> 00:44:54.000 but I also tell this router that, 00:44:55.000 --> 00:44:56.000 and any other router in the area 00:44:57.000 --> 00:44:58.000 that I've turned it into a not-so-stubby area. 00:44:59.000 --> 00:45:00.000 By doing so, 00:45:01.000 --> 00:45:02.000 then it turns on the stub area flag. 00:45:03.000 --> 00:45:04.000 If this has the stub area flag set, 00:45:05.000 --> 00:45:06.000 but I failed to do it over here, 00:45:07.000 --> 00:45:09.000 then we can't form a neighbor adjacency with this. 00:45:09.000 --> 00:45:11.000 We can't form a neighbor adjacency with each other. 00:45:12.000 --> 00:45:13.000 So they have to match. 00:45:14.000 --> 00:45:15.000 The stub area flag must match. 00:45:16.000 --> 00:45:21.000 And you'll learn about these in NRC, not here. 00:45:33.000 --> 00:45:34.000 Okay. 00:45:35.000 --> 00:45:37.000 I think we've got you covered for this page. 00:45:38.000 --> 00:45:40.000 Must be unique, must match, must match, 00:45:41.000 --> 00:45:43.000 subnet, must match, MTU. 00:45:44.000 --> 00:45:45.000 Okay, we're good. 00:45:46.000 --> 00:45:47.000 All right. 00:45:48.000 --> 00:45:49.000 So it's really important, 00:45:50.000 --> 00:45:51.000 because as we get to our discussion tomorrow as well, 00:45:52.000 --> 00:45:53.000 you're going to see when we do our configs, 00:45:54.000 --> 00:45:55.000 interface-based, things are going to have to match, 00:45:56.000 --> 00:45:57.000 things unique, all these different types of stuff. 00:45:58.000 --> 00:45:59.000 And I'll remind you about all of that tomorrow. 00:46:00.000 --> 00:46:01.000 But now that we've got this covered, 00:46:02.000 --> 00:46:03.000 wait, we've got to come back to here. 00:46:04.000 --> 00:46:05.000 So now where are we? 00:46:06.000 --> 00:46:07.000 We're at the two-way state, that's it. 00:46:08.000 --> 00:46:09.000 We're at the two-way state. 00:46:10.000 --> 00:46:11.000 We still haven't even exchanged anything with each other, 00:46:12.000 --> 00:46:13.000 have we? 00:46:14.000 --> 00:46:15.000 No, nothing. 00:46:16.000 --> 00:46:17.000 We've only done the hello packet. 00:46:18.000 --> 00:46:20.000 So now what has to happen next? 00:46:21.000 --> 00:46:24.000 So for every neighborhood that is being formed, 00:46:25.000 --> 00:46:27.000 so what does that mean? 00:46:28.000 --> 00:46:29.000 It means, don't forget, 00:46:30.000 --> 00:46:31.000 if we had another router here, 00:46:32.000 --> 00:46:33.000 another router here, 00:46:34.000 --> 00:46:36.000 another router here, 00:46:37.000 --> 00:46:38.000 so there's a neighborhood that's going to be formed here, 00:46:39.000 --> 00:46:40.000 a neighborhood that's formed here, 00:46:41.000 --> 00:46:42.000 a neighborhood that's formed here, 00:46:43.000 --> 00:46:44.000 a neighborhood that's formed here, 00:46:45.000 --> 00:46:46.000 a neighborhood that's formed here. 00:46:47.000 --> 00:46:49.000 So for all of those neighborhoods 00:46:50.000 --> 00:46:51.000 that are being formed, 00:46:52.000 --> 00:46:54.000 we have to go through this. 00:46:55.000 --> 00:46:56.000 So hello for each of these, 00:46:57.000 --> 00:46:58.000 and then we have to go through here. 00:46:59.000 --> 00:47:00.000 So for example, 00:47:01.000 --> 00:47:03.000 these two routers now… 00:47:04.000 --> 00:47:06.000 are going to move into the Xstart state 00:47:07.000 --> 00:47:08.000 because they have established bidirectional communication. 00:47:09.000 --> 00:47:10.000 At the same time, 00:47:11.000 --> 00:47:12.000 these two routers 00:47:13.000 --> 00:47:15.000 could be going into the Xstart state as well. 00:47:16.000 --> 00:47:18.000 But each of these are going to be handled 00:47:19.000 --> 00:47:21.000 independently of each other, 00:47:22.000 --> 00:47:23.000 meaning that what happens here 00:47:24.000 --> 00:47:25.000 does not interfere with what's happening here, 00:47:26.000 --> 00:47:27.000 or here, or here, or here. 00:47:28.000 --> 00:47:30.000 What is the Xstart phase? 00:47:33.000 --> 00:47:34.000 A good way to think about it 00:47:35.000 --> 00:47:36.000 is rock, paper, scissors. 00:47:39.000 --> 00:47:41.000 These two devices are trying to figure out 00:47:42.000 --> 00:47:44.000 who is going to be in charge 00:47:45.000 --> 00:47:46.000 of the conversation. 00:47:47.000 --> 00:47:49.000 Because if we are both in charge 00:47:50.000 --> 00:47:51.000 of the conversation, 00:47:52.000 --> 00:47:53.000 it could lead to conflicts, 00:47:54.000 --> 00:47:56.000 and it could lead to conflict. 00:47:57.000 --> 00:47:59.000 Non-accurate results. 00:48:00.000 --> 00:48:01.000 So these two routers are going to figure out 00:48:02.000 --> 00:48:03.000 who is in charge of the conversation, 00:48:04.000 --> 00:48:05.000 and these two routers would determine 00:48:06.000 --> 00:48:07.000 who is in charge of this conversation. 00:48:08.000 --> 00:48:10.000 And who determines, 00:48:11.000 --> 00:48:12.000 or who wins? 00:48:13.000 --> 00:48:14.000 Well, they don't really play rock, paper, scissors, 00:48:15.000 --> 00:48:16.000 but whoever has the higher router ID. 00:48:17.000 --> 00:48:19.000 Whoever has the higher router ID 00:48:20.000 --> 00:48:21.000 is the one that is going to be in charge 00:48:22.000 --> 00:48:23.000 of the conversation. 00:48:24.000 --> 00:48:25.000 So between this relationship, 00:48:25.000 --> 00:48:26.000 it would more than likely be this router 00:48:27.000 --> 00:48:28.000 if its router ID was 0002. 00:48:29.000 --> 00:48:30.000 Let's say this one was 0003, 00:48:31.000 --> 00:48:32.000 then this one would be in charge 00:48:33.000 --> 00:48:34.000 of the conversation between these two, 00:48:35.000 --> 00:48:36.000 because its router ID is 0003. 00:48:41.000 --> 00:48:43.000 Let's say this one is 0009, 00:48:44.000 --> 00:48:46.000 this one is 0005, 00:48:47.000 --> 00:48:48.000 and this one is 0004, 00:48:49.000 --> 00:48:51.000 then this one right here 00:48:52.000 --> 00:48:53.000 would be in charge of this conversation, 00:48:53.000 --> 00:48:54.000 and this conversation. 00:48:55.000 --> 00:48:56.000 Now, if you're wondering why I'm doing those 00:48:57.000 --> 00:48:58.000 for router IDs, we'll cover that tomorrow. 00:48:59.000 --> 00:49:00.000 If you're wondering, hey, where is he getting 00:49:01.000 --> 00:49:02.000 these router ID numbers from, 00:49:03.000 --> 00:49:04.000 we'll cover that tomorrow. 00:49:05.000 --> 00:49:06.000 So the X start state, rock, paper, scissors, 00:49:07.000 --> 00:49:08.000 essentially, whoever has the higher router ID 00:49:09.000 --> 00:49:10.000 between the two routers 00:49:11.000 --> 00:49:12.000 is the one that's going to be in charge 00:49:13.000 --> 00:49:14.000 of the conversation. 00:49:15.000 --> 00:49:16.000 So now that we've established 00:49:17.000 --> 00:49:18.000 who's in charge of the conversation, 00:49:19.000 --> 00:49:20.000 then we go to the exchange phase. 00:49:21.000 --> 00:49:22.000 The exchange phase is when the router 00:49:23.000 --> 00:49:24.000 with the higher router ID 00:49:25.000 --> 00:49:27.000 sends its database descriptor packet first, 00:49:28.000 --> 00:49:30.000 and then we send an LSAC back 00:49:31.000 --> 00:49:32.000 to acknowledge that we got it. 00:49:33.000 --> 00:49:34.000 And then we can send 00:49:35.000 --> 00:49:36.000 a database descriptor packet to you, 00:49:37.000 --> 00:49:38.000 and you can acknowledge that you got it. 00:49:41.000 --> 00:49:45.000 If you ever see your routers stuck, 00:49:46.000 --> 00:49:47.000 if you ever get stuck here, 00:49:48.000 --> 00:49:49.000 if you ever get stuck here, 00:49:50.000 --> 00:49:51.000 and when you're looking 00:49:52.000 --> 00:49:54.000 at your interface outputs, 00:49:55.000 --> 00:49:58.000 for example, if you were looking at 00:49:59.000 --> 00:50:02.000 do show IP OSPF neighbor, 00:50:03.000 --> 00:50:06.000 if you were looking here, 00:50:07.000 --> 00:50:08.000 and you saw, for example, 00:50:09.000 --> 00:50:12.000 exchange or X start state, 00:50:12.000 --> 00:50:15.000 then that means you have an MTU mismatch. 00:50:16.000 --> 00:50:17.000 That's what that means. 00:50:18.000 --> 00:50:19.000 And that's what I would want you 00:50:20.000 --> 00:50:21.000 to remember for the exam. 00:50:24.000 --> 00:50:26.000 Is it possible that you could get stuck here 00:50:27.000 --> 00:50:28.000 for other reasons, 00:50:29.000 --> 00:50:30.000 like maybe a mismatched network type 00:50:31.000 --> 00:50:32.000 or mismatched area? 00:50:33.000 --> 00:50:35.000 No, because in those scenarios, 00:50:36.000 --> 00:50:37.000 you would actually not even get past 00:50:38.000 --> 00:50:39.000 the two-way state. 00:50:39.000 --> 00:50:40.000 You would not even get past 00:50:41.000 --> 00:50:42.000 the two-way state. 00:50:43.000 --> 00:50:44.000 You might not even get past 00:50:45.000 --> 00:50:46.000 the init state. 00:50:47.000 --> 00:50:48.000 You would get stuck in down, 00:50:49.000 --> 00:50:51.000 init, two-way, init, two-way, init, two-way, 00:50:52.000 --> 00:50:53.000 if you had mismatched network type 00:50:54.000 --> 00:50:55.000 or mismatched areas, 00:50:56.000 --> 00:50:57.000 or you might not even see anything at all, 00:50:58.000 --> 00:50:59.000 any state at all. 00:51:05.000 --> 00:51:06.000 So for the exam, 00:51:06.000 --> 00:51:07.000 X start exchange 00:51:08.000 --> 00:51:09.000 typically means MTU mismatch. 00:51:10.000 --> 00:51:11.000 Look for that. 00:51:12.000 --> 00:51:13.000 More than likely, that's the answer 00:51:14.000 --> 00:51:15.000 that you're going to want to pick. 00:51:16.000 --> 00:51:17.000 Let me show you what that would look like right here. 00:51:18.000 --> 00:51:19.000 So let's go to interface, 00:51:20.000 --> 00:51:21.000 fastethernet0 slash, 00:51:22.000 --> 00:51:23.000 what is it, 1 slash 0, we said. 00:51:24.000 --> 00:51:27.000 And let's say IPMTU 1400. 00:51:29.000 --> 00:51:30.000 Let's shut down the interface. 00:51:31.000 --> 00:51:32.000 And if we no shut the interface, 00:51:34.000 --> 00:51:35.000 bring it back up, 00:51:36.000 --> 00:51:37.000 see if this worked. 00:51:42.000 --> 00:51:43.000 So I'm in init right now. 00:51:47.000 --> 00:51:48.000 X start. 00:51:50.000 --> 00:51:51.000 And we're not going to get beyond that. 00:51:52.000 --> 00:51:53.000 So if you ever see output like this 00:51:54.000 --> 00:51:56.000 on any Cisco router certification exam 00:51:57.000 --> 00:51:59.000 where it says X start or exchange, 00:52:00.000 --> 00:52:01.000 let's see if it says exchange here. 00:52:07.000 --> 00:52:08.000 No, X start on this one right now. 00:52:09.000 --> 00:52:10.000 All right, but there are times 00:52:11.000 --> 00:52:12.000 where you'll see exchange. 00:52:13.000 --> 00:52:15.000 But it happens so fast that you've got to, 00:52:16.000 --> 00:52:17.000 you've got to be hitting enter 00:52:18.000 --> 00:52:19.000 at the exact right time to see exchange. 00:52:20.000 --> 00:52:21.000 I'm probably not going to get it today. 00:52:22.000 --> 00:52:24.000 All right, but anyways, you see X start or exchange. 00:52:25.000 --> 00:52:26.000 I immediately want you to gravitate 00:52:27.000 --> 00:52:29.000 towards MTU mismatch on the exam. 00:52:37.000 --> 00:52:41.000 All right, so we've successfully exchanged our DVDs. 00:52:45.000 --> 00:52:46.000 Now we analyze them 00:52:48.000 --> 00:52:50.000 and we identify what we don't know. 00:52:51.000 --> 00:52:52.000 So if you have something here, 00:52:53.000 --> 00:52:55.000 a DVD that I don't already have in my database, 00:52:56.000 --> 00:52:58.000 then I'll send you an LSR, meaning, 00:52:59.000 --> 00:53:00.000 hey, give me the details for this. 00:53:01.000 --> 00:53:03.000 So give me the LSA for this network. 00:53:03.000 --> 00:53:04.000 And so we do that with each other. 00:53:05.000 --> 00:53:06.000 And then we exchange the LSUs 00:53:07.000 --> 00:53:09.000 that have the LSAs in the loading phase. 00:53:10.000 --> 00:53:11.000 And then once that is done, what does it mean? 00:53:12.000 --> 00:53:13.000 It means I know everything that you know 00:53:14.000 --> 00:53:15.000 and you know everything that I know. 00:53:16.000 --> 00:53:19.000 Therefore, we are fully synchronized with each other, 00:53:20.000 --> 00:53:22.000 fully synchronized with each other. 00:53:34.000 --> 00:53:37.000 So know about those states. 00:53:38.000 --> 00:53:39.000 Oh, we missed one, didn't we? 00:53:40.000 --> 00:53:41.000 Yeah, know about those states for the certification exam. 00:53:42.000 --> 00:53:43.000 I just thought about it. 00:53:44.000 --> 00:53:45.000 Can I skip attempt? 00:53:46.000 --> 00:53:48.000 I attempted to avoid attempt. 00:53:49.000 --> 00:53:51.000 All right, so when does attempt come into play? 00:53:52.000 --> 00:53:55.000 So the process for the certification exam 00:53:56.000 --> 00:53:58.000 is the same as the certification exam. 00:53:58.000 --> 00:54:00.000 All right, so when does attempt come into play? 00:54:01.000 --> 00:54:05.000 So the process I just explained to you 00:54:06.000 --> 00:54:10.000 is for dynamic neighborhoods. 00:54:13.000 --> 00:54:15.000 Now, why is it a dynamic neighborhood? 00:54:16.000 --> 00:54:19.000 Because I enable OSPF on that interface. 00:54:20.000 --> 00:54:24.000 My hello packet gets sent out to 224005. 00:54:24.000 --> 00:54:28.000 Any device in that subnet VLAN broadcast domain 00:54:29.000 --> 00:54:32.000 that's also participating in OSPF will receive that 00:54:33.000 --> 00:54:35.000 and dynamically form a neighborship with me. 00:54:36.000 --> 00:54:37.000 That's how it works. 00:54:38.000 --> 00:54:39.000 So it's dynamic. 00:54:40.000 --> 00:54:42.000 At any point in time have I explicitly stated 00:54:43.000 --> 00:54:44.000 who my neighbors are? 00:54:45.000 --> 00:54:46.000 The answer is no. 00:54:47.000 --> 00:54:50.000 So down init 2a is dynamic neighborhoods. 00:54:51.000 --> 00:54:53.000 However, you may have, for example, a router 00:54:54.000 --> 00:54:56.000 that is connected over a wide area network, 00:54:57.000 --> 00:54:59.000 connected to another router over here, 00:55:01.000 --> 00:55:07.000 and multicast not supported, 00:55:08.000 --> 00:55:11.000 meaning your service provider is like no multicast, 00:55:12.000 --> 00:55:13.000 new multicast. 00:55:14.000 --> 00:55:15.000 So can you do dynamic neighborhoods 00:55:16.000 --> 00:55:17.000 if multicast is not supported? 00:55:18.000 --> 00:55:19.000 No, you can't. 00:55:20.000 --> 00:55:21.000 So what you have to do in this case 00:55:22.000 --> 00:55:23.000 is on this router in OSPF 00:55:24.000 --> 00:55:26.000 you're going to have to use the neighbor command 00:55:27.000 --> 00:55:30.000 and you are going to have to explicitly define your neighbors 00:55:31.000 --> 00:55:33.000 based on their IP address. 00:55:34.000 --> 00:55:38.000 So let's say the IP address was 203.0.113.9 00:55:39.000 --> 00:55:42.000 and this one over here is 192.0.2.5. 00:55:43.000 --> 00:55:52.000 Then I would say neighbor 203.0.113.9, etc., 00:55:52.000 --> 00:55:53.000 whatever other options are. 00:55:54.000 --> 00:55:55.000 There are a few other options you can add for that. 00:55:56.000 --> 00:55:57.000 But in the end I'm pointing to you 00:55:58.000 --> 00:55:59.000 and then you would do the same thing. 00:56:00.000 --> 00:56:01.000 Oops, I put in my own address, silly me. 00:56:02.000 --> 00:56:04.000 Neighbor 192.0.2.5 00:56:05.000 --> 00:56:06.000 and over here we type in neighbor 00:56:07.000 --> 00:56:09.000 and then 203.0.113.9. 00:56:10.000 --> 00:56:11.000 So now I send a what? 00:56:12.000 --> 00:56:13.000 A unicast. 00:56:14.000 --> 00:56:15.000 Unicast to you. 00:56:16.000 --> 00:56:17.000 You send a unicast to me. 00:56:18.000 --> 00:56:19.000 So it's not multicast anymore, it's unicasted. 00:56:19.000 --> 00:56:20.000 So with the attempt phase, 00:56:21.000 --> 00:56:22.000 you would go down, 00:56:23.000 --> 00:56:24.000 then you'd go to attempt. 00:56:25.000 --> 00:56:27.000 Attempt means that you sent your unicast hello 00:56:28.000 --> 00:56:30.000 but you have not received one from the neighbor yet. 00:56:31.000 --> 00:56:33.000 So you've sent your unicast hello 00:56:34.000 --> 00:56:35.000 but you haven't received one from the neighbor yet. 00:56:36.000 --> 00:56:37.000 So if you've sent one, you go to attempt 00:56:38.000 --> 00:56:40.000 and then once you receive one, then you go two-way. 00:56:41.000 --> 00:56:42.000 That's how you do that. 00:56:43.000 --> 00:56:44.000 So I send it, I go attempt. 00:56:45.000 --> 00:56:46.000 When I receive one from you, then I'm two-way. 00:56:47.000 --> 00:56:48.000 So that's probably not going to come up 00:56:49.000 --> 00:56:50.000 on the certification exam. 00:56:52.000 --> 00:56:54.000 In Encore, it more than likely will in an RC, 00:56:55.000 --> 00:56:56.000 the 300-410 exam, 00:56:57.000 --> 00:56:58.000 but not for Encore. 00:56:59.000 --> 00:57:01.000 Encore pretty much focuses on dynamic neighborships. 00:57:05.000 --> 00:57:06.000 All right. 00:57:07.000 --> 00:57:08.000 So know a lot, as you can see, 00:57:10.000 --> 00:57:11.000 to get ready for the exam. 00:57:12.000 --> 00:57:14.000 All right, so now we'll talk about OSPF design. 00:57:15.000 --> 00:57:16.000 To wrap up today 00:57:18.000 --> 00:57:20.000 and the beginning of our OSPF discussion. 00:57:22.000 --> 00:57:25.000 So when we have OSPF running in our environment, 00:57:28.000 --> 00:57:29.000 we have the opportunity 00:57:30.000 --> 00:57:31.000 of either doing a single-area deployment 00:57:32.000 --> 00:57:33.000 or a multi-area deployment. 00:57:35.000 --> 00:57:36.000 Anybody here using OSPF 00:57:38.000 --> 00:57:40.000 in only a single deployment? 00:57:41.000 --> 00:57:42.000 If you are, 00:57:42.000 --> 00:57:43.000 type in single. 00:57:44.000 --> 00:57:45.000 If not, type in multi. 00:57:46.000 --> 00:57:47.000 I just like to get an idea 00:57:48.000 --> 00:57:49.000 of what's going on here. 00:57:54.000 --> 00:57:55.000 So, 00:57:56.000 --> 00:57:57.000 what is the primary difference 00:57:58.000 --> 00:57:59.000 between the two? 00:58:00.000 --> 00:58:01.000 It's scalability. 00:58:02.000 --> 00:58:03.000 That's really what it is. 00:58:05.000 --> 00:58:06.000 It's scalability. 00:58:07.000 --> 00:58:08.000 The more networks you have 00:58:10.000 --> 00:58:11.000 in OSPF, 00:58:13.000 --> 00:58:14.000 the less scalable it becomes 00:58:16.000 --> 00:58:17.000 when you are single-area only. 00:58:21.000 --> 00:58:22.000 Let me repeat that. 00:58:23.000 --> 00:58:24.000 The more networks you have, 00:58:27.000 --> 00:58:28.000 the less scalable OSPF is. 00:58:30.000 --> 00:58:31.000 The more networks you have, 00:58:32.000 --> 00:58:33.000 the less scalable OSPF is. 00:58:33.000 --> 00:58:34.000 The less scalable OSPF becomes 00:58:36.000 --> 00:58:37.000 when you are single-area. 00:58:41.000 --> 00:58:42.000 Let me just show you 00:58:43.000 --> 00:58:44.000 a visual representation 00:58:45.000 --> 00:58:46.000 of the difference between single-area 00:58:47.000 --> 00:58:48.000 and multi-area. 00:58:49.000 --> 00:58:50.000 So these are all of our routers 00:58:51.000 --> 00:58:52.000 in our OSPF routing domain. 00:58:54.000 --> 00:58:55.000 These are all the routers 00:58:56.000 --> 00:58:57.000 in our OSPF routing domain. 00:58:58.000 --> 00:58:59.000 Every one of our routers 00:59:00.000 --> 00:59:01.000 are in the exact same area 00:59:01.000 --> 00:59:02.000 in this diagram. 00:59:09.000 --> 00:59:10.000 Multi-area with the same routers 00:59:11.000 --> 00:59:12.000 would look maybe something like this. 00:59:16.000 --> 00:59:17.000 More scalable, 00:59:18.000 --> 00:59:20.000 virtually unlimited scalability 00:59:22.000 --> 00:59:24.000 versus limited scalability. 00:59:26.000 --> 00:59:27.000 Why is that? 00:59:28.000 --> 00:59:29.000 It's simply because of how OSPF 00:59:30.000 --> 00:59:31.000 behaves, 00:59:32.000 --> 00:59:33.000 simply because of how OSPF behaves. 00:59:38.000 --> 00:59:39.000 Let's say we have a network here, 00:59:40.000 --> 00:59:41.000 10.0.0.0 slash 24. 00:59:49.000 --> 00:59:50.000 Let's say 00:59:51.000 --> 00:59:52.000 that for some reason 00:59:53.000 --> 00:59:54.000 the transceiver of this interface 00:59:56.000 --> 00:59:57.000 starts to go a little haywire. 00:59:59.000 --> 01:00:00.000 Doesn't matter why. 01:00:01.000 --> 01:00:02.000 What would happen 01:00:03.000 --> 01:00:04.000 potentially to this interface? 01:00:05.000 --> 01:00:06.000 Well, the interface might go up, 01:00:07.000 --> 01:00:08.000 then down, 01:00:08.000 --> 01:00:09.000 then up, then down, 01:00:09.000 --> 01:00:10.000 then up, then down, 01:00:10.000 --> 01:00:11.000 then up, then down, 01:00:11.000 --> 01:00:12.000 then up, then down, 01:00:12.000 --> 01:00:13.000 then up, then down, then up. 01:00:13.000 --> 01:00:14.000 Okay. 01:00:14.000 --> 01:00:16.000 How does that affect potentially OSPF? 01:00:18.000 --> 01:00:19.000 Well, 01:00:21.000 --> 01:00:22.000 this router, 01:00:26.000 --> 01:00:27.000 every time there's a change 01:00:30.000 --> 01:00:31.000 to an OSPF-enabled interface, 01:00:34.000 --> 01:00:35.000 it has to send out 01:00:37.000 --> 01:00:38.000 a Type I LSA. 01:00:44.000 --> 01:00:45.000 And we'll talk more about LSAs later on, 01:00:46.000 --> 01:00:47.000 tomorrow. 01:00:48.000 --> 01:00:49.000 But a Type I LSA 01:00:50.000 --> 01:00:51.000 is the most fundamental LSA type. 01:00:53.000 --> 01:00:54.000 Now, I'm not talking about packet types here. 01:00:55.000 --> 01:00:56.000 I'm talking about LSA types now. 01:00:57.000 --> 01:00:58.000 This is what we call the router LSA. 01:01:00.000 --> 01:01:01.000 And a router LSA 01:01:02.000 --> 01:01:03.000 is used by every router 01:01:04.000 --> 01:01:05.000 to notify all the other routers 01:01:06.000 --> 01:01:07.000 in the same area about itself. 01:01:09.000 --> 01:01:10.000 So this area has all these routers in it. 01:01:11.000 --> 01:01:12.000 So all of these routers 01:01:13.000 --> 01:01:14.000 would have received 01:01:14.000 --> 01:01:15.000 this router's Type I LSA 01:01:16.000 --> 01:01:17.000 at some point in time. 01:01:19.000 --> 01:01:20.000 So every router generates a Type I LSA, 01:01:22.000 --> 01:01:23.000 and it gets flooded to everyone else 01:01:24.000 --> 01:01:25.000 in the area. 01:01:29.000 --> 01:01:30.000 That's how every router 01:01:31.000 --> 01:01:32.000 learns about every other router. 01:01:34.000 --> 01:01:35.000 And that's how they build 01:01:35.000 --> 01:01:36.000 their topological map. 01:01:37.000 --> 01:01:38.000 So now every router knows 01:01:38.000 --> 01:01:39.000 where everybody else is. 01:01:39.000 --> 01:01:40.000 They know who's connected to who 01:01:40.000 --> 01:01:41.000 just by looking at that Type I LSA. 01:01:42.000 --> 01:01:43.000 Oh, well, if that's you 01:01:43.000 --> 01:01:44.000 and you are connected to this network 01:01:44.000 --> 01:01:45.000 and that's that one, 01:01:45.000 --> 01:01:46.000 and that one's connected to that network, 01:01:46.000 --> 01:01:47.000 that means you're connected together. 01:01:49.000 --> 01:01:50.000 Or else that wouldn't exist. 01:01:51.000 --> 01:01:52.000 So it could put all the pieces 01:01:52.000 --> 01:01:53.000 of the puzzle together. 01:01:53.000 --> 01:01:54.000 So think of all the Type I LSAs 01:01:54.000 --> 01:01:55.000 as puzzle pieces, 01:01:56.000 --> 01:01:57.000 and every router has to put 01:01:57.000 --> 01:01:58.000 all the puzzle pieces together. 01:01:59.000 --> 01:02:00.000 So if this network's flapping, 01:02:01.000 --> 01:02:02.000 I have to now let everybody 01:02:02.000 --> 01:02:03.000 know about that. 01:02:04.000 --> 01:02:05.000 The problem with the Type I LSA 01:02:06.000 --> 01:02:07.000 is that any time you build 01:02:09.000 --> 01:02:10.000 a Type I LSA 01:02:11.000 --> 01:02:12.000 and send it to everyone, 01:02:15.000 --> 01:02:16.000 you know what they have to do? 01:02:17.000 --> 01:02:18.000 They have to rebuild the puzzle. 01:02:21.000 --> 01:02:22.000 The whole puzzle. 01:02:24.000 --> 01:02:25.000 The whole puzzle. 01:02:25.000 --> 01:02:26.000 The whole puzzle. 01:02:29.000 --> 01:02:30.000 So that means 01:02:31.000 --> 01:02:32.000 every one of these routers 01:02:32.000 --> 01:02:33.000 have to take every other puzzle piece 01:02:34.000 --> 01:02:35.000 and the one you just sent them 01:02:36.000 --> 01:02:37.000 and redo all the calculations 01:02:38.000 --> 01:02:39.000 and put the puzzle back together 01:02:40.000 --> 01:02:41.000 and run Dijkstra's 01:02:41.000 --> 01:02:42.000 shortest path first algorithm 01:02:43.000 --> 01:02:44.000 as you stated. 01:02:44.000 --> 01:02:45.000 That's right. 01:02:46.000 --> 01:02:47.000 SPF needs to be recalculated 01:02:48.000 --> 01:02:49.000 by every router. 01:02:50.000 --> 01:02:51.000 Every router. 01:02:52.000 --> 01:02:53.000 So now imagine 01:02:53.000 --> 01:02:54.000 if you had something 01:02:54.000 --> 01:02:55.000 going on there 01:02:57.000 --> 01:02:58.000 and you had one area 01:02:58.000 --> 01:02:59.000 that means every router. 01:02:59.000 --> 01:03:00.000 What if you had 01:03:00.000 --> 01:03:01.000 a thousand routers? 01:03:02.000 --> 01:03:03.000 Every router has to do 01:03:03.000 --> 01:03:04.000 a calculation based on that. 01:03:04.000 --> 01:03:05.000 Now if it's flapping, 01:03:05.000 --> 01:03:06.000 oh my gosh, 01:03:06.000 --> 01:03:07.000 up, down, up, down, up, down, 01:03:07.000 --> 01:03:08.000 calculate, calculate, calculate, 01:03:08.000 --> 01:03:09.000 calculate, calculate, 01:03:09.000 --> 01:03:10.000 because every time 01:03:10.000 --> 01:03:11.000 it goes up, down, 01:03:11.000 --> 01:03:12.000 new Type I LSA, 01:03:12.000 --> 01:03:13.000 new Type I LSA, 01:03:13.000 --> 01:03:14.000 new Type I LSA, 01:03:14.000 --> 01:03:15.000 new Type I LSA. 01:03:15.000 --> 01:03:16.000 You see how this could be 01:03:16.000 --> 01:03:17.000 very detrimental 01:03:17.000 --> 01:03:18.000 because the larger the network, 01:03:19.000 --> 01:03:20.000 the possibility of having 01:03:20.000 --> 01:03:21.000 some issues in different places 01:03:21.000 --> 01:03:22.000 at the same time 01:03:22.000 --> 01:03:23.000 are significantly high. 01:03:24.000 --> 01:03:25.000 So in single area, 01:03:26.000 --> 01:03:27.000 yeah, this could be 01:03:27.000 --> 01:03:28.000 very, very, very, very 01:03:29.000 --> 01:03:30.000 performance 01:03:31.000 --> 01:03:32.000 reducing 01:03:32.000 --> 01:03:33.000 having a single area. 01:03:34.000 --> 01:03:35.000 So scalability 01:03:36.000 --> 01:03:37.000 kind of 01:03:38.000 --> 01:03:39.000 wears out over time. 01:03:40.000 --> 01:03:41.000 Now back in the day 01:03:41.000 --> 01:03:42.000 we used to say, 01:03:42.000 --> 01:03:43.000 oh, no more than 01:03:43.000 --> 01:03:44.000 50 routers in an area. 01:03:45.000 --> 01:03:46.000 I mean, that's a lot 01:03:46.000 --> 01:03:47.000 of routers, folks, 01:03:47.000 --> 01:03:48.000 even for a ginormous 01:03:49.000 --> 01:03:50.000 enterprise to have 01:03:50.000 --> 01:03:51.000 50 routers in a single area. 01:03:53.000 --> 01:03:54.000 Right? 01:03:54.000 --> 01:03:55.000 That's a lot, okay? 01:03:56.000 --> 01:03:57.000 And in reality today 01:03:57.000 --> 01:03:58.000 with our routers, 01:03:59.000 --> 01:04:00.000 think about how amazing 01:04:00.000 --> 01:04:01.000 our high-end routers are. 01:04:02.000 --> 01:04:03.000 They are ridiculously 01:04:03.000 --> 01:04:04.000 fast and efficient, 01:04:05.000 --> 01:04:06.000 meaning we could probably have 01:04:07.000 --> 01:04:08.000 200 routers in an area today 01:04:09.000 --> 01:04:10.000 and not really have 01:04:10.000 --> 01:04:11.000 to worry about it. 01:04:23.000 --> 01:04:24.000 But the best 01:04:27.000 --> 01:04:28.000 practice 01:04:29.000 --> 01:04:30.000 is to keep your areas 01:04:31.000 --> 01:04:32.000 small. 01:04:32.000 --> 01:04:33.000 Keep your areas 01:04:33.000 --> 01:04:34.000 tight. 01:04:37.000 --> 01:04:38.000 Why? 01:04:38.000 --> 01:04:39.000 You get virtually 01:04:39.000 --> 01:04:40.000 unlimited scalability. 01:04:42.000 --> 01:04:43.000 So in that case, 01:04:43.000 --> 01:04:44.000 it means now 01:04:44.000 --> 01:04:45.000 if I have an issue 01:04:46.000 --> 01:04:47.000 here, 01:04:53.000 --> 01:04:54.000 how far does the 01:04:54.000 --> 01:04:55.000 Type 1 LSA go? 01:05:02.000 --> 01:05:03.000 As we will talk about 01:05:03.000 --> 01:05:04.000 tomorrow, the Type 1 LSA 01:05:05.000 --> 01:05:06.000 only gets flooded 01:05:09.000 --> 01:05:10.000 in the area 01:05:11.000 --> 01:05:12.000 it was created. 01:05:13.000 --> 01:05:14.000 So only these two 01:05:14.000 --> 01:05:15.000 routers have to 01:05:16.000 --> 01:05:17.000 rebuild the puzzle. 01:05:17.000 --> 01:05:18.000 No one else does. 01:05:20.000 --> 01:05:21.000 Now you might be saying, 01:05:21.000 --> 01:05:22.000 well then how do all 01:05:22.000 --> 01:05:23.000 the other routers know 01:05:23.000 --> 01:05:24.000 about the change? 01:05:24.000 --> 01:05:25.000 That's where the awesome 01:05:25.000 --> 01:05:26.000 stuff comes into play. 01:05:26.000 --> 01:05:27.000 You see this router here 01:05:27.000 --> 01:05:28.000 is called an area border 01:05:28.000 --> 01:05:29.000 router, 01:05:29.000 --> 01:05:30.000 and it's going to 01:05:30.000 --> 01:05:31.000 generate what are called 01:05:31.000 --> 01:05:32.000 Type 3 LSAs 01:05:33.000 --> 01:05:34.000 instead. 01:05:34.000 --> 01:05:35.000 So this network 01:05:36.000 --> 01:05:37.000 in here is a Type 1, 01:05:38.000 --> 01:05:39.000 but this network 01:05:39.000 --> 01:05:40.000 everywhere else 01:05:41.000 --> 01:05:42.000 is a Type 3. 01:05:43.000 --> 01:05:44.000 And Type 3s are 01:05:44.000 --> 01:05:45.000 basically this. 01:05:46.000 --> 01:05:47.000 They're basically this 01:05:47.000 --> 01:05:48.000 router saying, 01:05:48.000 --> 01:05:49.000 hey everybody, 01:05:49.000 --> 01:05:50.000 woohoo, 01:05:50.000 --> 01:05:51.000 I know about 01:05:51.000 --> 01:05:52.000 10.0.0.24, 01:05:52.000 --> 01:05:53.000 so if you want to 01:05:53.000 --> 01:05:54.000 go to it, 01:05:54.000 --> 01:05:55.000 send your traffic to me. 01:05:55.000 --> 01:05:56.000 Just send it to me. 01:05:56.000 --> 01:05:57.000 I'll get you there 01:05:57.000 --> 01:05:58.000 through me over there 01:05:58.000 --> 01:05:59.000 somewhere. 01:06:00.000 --> 01:06:01.000 Who owns it? 01:06:01.000 --> 01:06:02.000 Doesn't matter who owns it. 01:06:02.000 --> 01:06:03.000 I'll get you to it. 01:06:04.000 --> 01:06:05.000 See the difference in 01:06:05.000 --> 01:06:06.000 behavior here? 01:06:06.000 --> 01:06:07.000 So now 01:06:07.000 --> 01:06:08.000 if this goes down, 01:06:08.000 --> 01:06:09.000 the Type 3 LSA 01:06:09.000 --> 01:06:10.000 gets generated 01:06:11.000 --> 01:06:12.000 and the rest of the 01:06:12.000 --> 01:06:13.000 routers just get 01:06:13.000 --> 01:06:14.000 updated. 01:06:14.000 --> 01:06:15.000 Hey, you know what guys? 01:06:15.000 --> 01:06:16.000 That 10.0.0 thing 01:06:16.000 --> 01:06:17.000 I sent you a while ago, 01:06:17.000 --> 01:06:18.000 it doesn't exist anymore. 01:06:18.000 --> 01:06:19.000 Delete it. 01:06:19.000 --> 01:06:20.000 Don't worry about it. 01:06:22.000 --> 01:06:23.000 That's it. 01:06:23.000 --> 01:06:24.000 You don't have to do a 01:06:25.000 --> 01:06:26.000 puzzle piece 01:06:26.000 --> 01:06:27.000 mathematical calculation 01:06:27.000 --> 01:06:28.000 anymore. 01:06:28.000 --> 01:06:29.000 Right? 01:06:29.000 --> 01:06:30.000 And then when it comes 01:06:30.000 --> 01:06:31.000 back up, 01:06:31.000 --> 01:06:32.000 you're like, 01:06:32.000 --> 01:06:33.000 oh sorry, 01:06:33.000 --> 01:06:34.000 my bad, 01:06:34.000 --> 01:06:35.000 my bad. 01:06:35.000 --> 01:06:36.000 Yeah, no, 01:06:36.000 --> 01:06:37.000 actually it's back now, 01:06:37.000 --> 01:06:38.000 so add it in 01:06:38.000 --> 01:06:39.000 and the metric for it 01:06:39.000 --> 01:06:40.000 is this. 01:06:40.000 --> 01:06:41.000 And based on the other 01:06:41.000 --> 01:06:42.000 stuff you know, 01:06:42.000 --> 01:06:43.000 just add two numbers, 01:06:43.000 --> 01:06:44.000 three numbers together 01:06:44.000 --> 01:06:45.000 and you're good to go. 01:06:45.000 --> 01:06:46.000 All right, 01:06:46.000 --> 01:06:47.000 cool. 01:06:47.000 --> 01:06:48.000 So that's the 01:06:48.000 --> 01:06:49.000 difference in mentality 01:06:49.000 --> 01:06:50.000 and behavior here. 01:06:50.000 --> 01:06:51.000 Yeah. 01:06:51.000 --> 01:06:52.000 Right, 01:06:52.000 --> 01:06:53.000 so that's why now 01:06:53.000 --> 01:06:54.000 when you even have 01:06:54.000 --> 01:06:55.000 more areas like we 01:06:55.000 --> 01:06:56.000 have here, 01:06:56.000 --> 01:06:57.000 you can see what 01:06:57.000 --> 01:06:58.000 happens in Area 51 01:06:58.000 --> 01:06:59.000 stays in Area 51 01:06:59.000 --> 01:07:00.000 and that's kind of 01:07:00.000 --> 01:07:01.000 true, 01:07:01.000 --> 01:07:02.000 right, 01:07:02.000 --> 01:07:03.000 in the United States. 01:07:03.000 --> 01:07:04.000 What happens in Area 51 01:07:04.000 --> 01:07:05.000 stays in Area 51. 01:07:05.000 --> 01:07:06.000 What happens in Area 113 01:07:06.000 --> 01:07:07.000 stays in Area 113. 01:07:07.000 --> 01:07:08.000 What happens in Area 7 01:07:08.000 --> 01:07:09.000 stays in Area 7. 01:07:09.000 --> 01:07:10.000 What happens in Area 0 01:07:10.000 --> 01:07:11.000 stays in Area 0. 01:07:11.000 --> 01:07:12.000 Right, 01:07:12.000 --> 01:07:13.000 so now if you have 01:07:13.000 --> 01:07:14.000 an issue in the area 01:07:14.000 --> 01:07:15.000 at all, 01:07:15.000 --> 01:07:16.000 if you have an issue 01:07:16.000 --> 01:07:17.000 in the area 01:07:17.000 --> 01:07:18.000 it only significantly 01:07:18.000 --> 01:07:19.000 affects the small area 01:07:19.000 --> 01:07:20.000 instead of every router. 01:07:20.000 --> 01:07:21.000 That's why you get that. 01:07:21.000 --> 01:07:22.000 Just something to keep 01:07:22.000 --> 01:07:23.000 in mind for the exam, 01:07:23.000 --> 01:07:24.000 right, 01:07:24.000 --> 01:07:25.000 we get to easily segment 01:07:25.000 --> 01:07:26.000 our network for greater 01:07:26.000 --> 01:07:27.000 scalability when it's all 01:07:27.000 --> 01:07:28.000 said and done. 01:07:28.000 --> 01:07:29.000 Now because of that 01:07:29.000 --> 01:07:30.000 we have to realize 01:07:30.000 --> 01:07:31.000 that OSPF really 01:07:31.000 --> 01:07:32.000 handcuffs us when it 01:07:32.000 --> 01:07:33.000 comes to design. 01:07:33.000 --> 01:07:34.000 What you're seeing here 01:07:34.000 --> 01:07:35.000 is that OSPF 01:07:35.000 --> 01:07:36.000 is not just 01:07:36.000 --> 01:07:37.000 a tool that 01:07:37.000 --> 01:07:38.000 you can use 01:07:38.000 --> 01:07:39.000 to help you 01:07:39.000 --> 01:07:40.000 understand 01:07:40.000 --> 01:07:41.000 what's going on 01:07:41.000 --> 01:07:42.000 in your network 01:07:42.000 --> 01:07:43.000 but it's also 01:07:43.000 --> 01:07:44.000 a tool that 01:07:44.000 --> 01:07:45.000 you can use 01:07:45.000 --> 01:07:46.000 to help you 01:07:46.000 --> 01:07:47.000 understand 01:07:47.000 --> 01:07:48.000 what's going on 01:07:48.000 --> 01:07:49.000 in your network. 01:07:49.000 --> 01:07:50.000 So what you're 01:07:50.000 --> 01:07:51.000 seeing here 01:07:51.000 --> 01:07:52.000 is the rule 01:07:52.000 --> 01:07:53.000 not the exception. 01:07:53.000 --> 01:07:54.000 When you have 01:07:54.000 --> 01:07:55.000 more than one area 01:07:55.000 --> 01:07:56.000 Area 0 01:07:56.000 --> 01:07:57.000 is the backbone. 01:07:57.000 --> 01:07:58.000 It is 01:07:58.000 --> 01:07:59.000 the center. 01:07:59.000 --> 01:08:00.000 It is 01:08:00.000 --> 01:08:01.000 what every other 01:08:01.000 --> 01:08:02.000 area connects to. 01:08:02.000 --> 01:08:03.000 Notice Area 1 01:08:03.000 --> 01:08:04.000 connects to 01:08:04.000 --> 01:08:05.000 Area 0. 01:08:05.000 --> 01:08:06.000 Area 51 01:08:06.000 --> 01:08:07.000 connects to 01:08:07.000 --> 01:08:08.000 Area 5. 01:08:08.000 --> 01:08:09.000 Area 6 01:08:09.000 --> 01:08:10.000 connects to 01:08:10.000 --> 01:08:11.000 Area 7. 01:08:11.000 --> 01:08:12.000 Area 7 01:08:12.000 --> 01:08:13.000 connects to 01:08:13.000 --> 01:08:14.000 Area 5. 01:08:14.000 --> 01:08:15.000 Area 51 01:08:15.000 --> 01:08:16.000 connects to 01:08:16.000 --> 01:08:17.000 Area 0. 01:08:17.000 --> 01:08:18.000 Area 113 01:08:18.000 --> 01:08:19.000 connects to 01:08:19.000 --> 01:08:20.000 Area 0. 01:08:20.000 --> 01:08:21.000 Area 7 01:08:21.000 --> 01:08:22.000 connects to 01:08:22.000 --> 01:08:23.000 Area 0. 01:08:23.000 --> 01:08:24.000 Notice we don't 01:08:24.000 --> 01:08:25.000 have this. 01:08:37.000 --> 01:08:38.000 You see that? 01:08:38.000 --> 01:08:39.000 We don't have that. 01:08:39.000 --> 01:08:42.000 Now can you do that? 01:08:42.000 --> 01:08:43.000 Sure. 01:08:43.000 --> 01:08:45.000 Will it work? 01:08:45.000 --> 01:08:47.000 Not by default. 01:08:47.000 --> 01:08:49.000 Is this a best practice? 01:08:49.000 --> 01:08:51.000 Absolutely not. 01:08:51.000 --> 01:08:52.000 Is it a band-aid 01:08:52.000 --> 01:08:53.000 to a problem you have 01:08:53.000 --> 01:08:54.000 that you can't solve 01:08:54.000 --> 01:08:55.000 any other way 01:08:55.000 --> 01:08:56.000 at this moment in time? 01:08:56.000 --> 01:08:57.000 Sure. 01:09:00.000 --> 01:09:01.000 The problem with this 01:09:01.000 --> 01:09:02.000 is that we have to create 01:09:02.000 --> 01:09:03.000 what is called 01:09:03.000 --> 01:09:05.000 a virtual link. 01:09:05.000 --> 01:09:06.000 I have to virtually 01:09:06.000 --> 01:09:08.000 connect this 01:09:09.000 --> 01:09:12.000 back up to Area 0. 01:09:12.000 --> 01:09:15.000 And this virtual connection 01:09:15.000 --> 01:09:18.000 would then be part of Area 0. 01:09:18.000 --> 01:09:21.000 I'm extending Area 0 out. 01:09:21.000 --> 01:09:23.000 Not redistribution. 01:09:23.000 --> 01:09:24.000 Absolutely not here. 01:09:24.000 --> 01:09:25.000 Not redistribution. 01:09:25.000 --> 01:09:27.000 I'm creating a virtual link 01:09:27.000 --> 01:09:29.000 to get this to work. 01:09:29.000 --> 01:09:30.000 The problem with a virtual link 01:09:30.000 --> 01:09:31.000 is that it goes through 01:09:31.000 --> 01:09:33.000 Area 113. 01:09:33.000 --> 01:09:34.000 And because it goes through 01:09:34.000 --> 01:09:35.000 Area 113, 01:09:35.000 --> 01:09:37.000 and we're extending Area 0 01:09:37.000 --> 01:09:38.000 through Area 113 01:09:38.000 --> 01:09:39.000 to connect this up to Area 0, 01:09:39.000 --> 01:09:40.000 my gosh. 01:09:40.000 --> 01:09:42.000 That puts extra pressure 01:09:42.000 --> 01:09:45.000 on Area 113. 01:09:45.000 --> 01:09:46.000 So Area 113 becomes 01:09:46.000 --> 01:09:49.000 like this transit area 01:09:49.000 --> 01:09:50.000 for Area 15. 01:09:50.000 --> 01:09:51.000 Although it can be done, 01:09:51.000 --> 01:09:52.000 again, 01:09:52.000 --> 01:09:54.000 not a proper design. 01:09:54.000 --> 01:09:55.000 It's a band-aid 01:09:55.000 --> 01:09:56.000 to a problem you have. 01:09:56.000 --> 01:09:57.000 Essentially, 01:09:57.000 --> 01:09:58.000 what you'd want to do 01:09:58.000 --> 01:09:59.000 is make sure that 01:09:59.000 --> 01:10:02.000 when you design Area 15, 01:10:02.000 --> 01:10:05.000 you hook it up right here. 01:10:05.000 --> 01:10:06.000 And have your router right here. 01:10:06.000 --> 01:10:08.000 Connect it up to your routers. 01:10:08.000 --> 01:10:11.000 However you can possibly do that. 01:10:11.000 --> 01:10:12.000 That would be better. 01:10:12.000 --> 01:10:13.000 So even if you had to do 01:10:13.000 --> 01:10:14.000 the virtual links, 01:10:14.000 --> 01:10:15.000 and I will, 01:10:15.000 --> 01:10:16.000 I believe I teach you 01:10:16.000 --> 01:10:27.000 about virtual links here. 01:10:27.000 --> 01:10:28.000 Nope. 01:10:28.000 --> 01:10:30.000 That is in NRC. 01:10:30.000 --> 01:10:34.000 I don't see it here. 01:10:34.000 --> 01:10:35.000 Nope. 01:10:35.000 --> 01:10:36.000 That's covered in NRC. 01:10:36.000 --> 01:10:37.000 Not even here. 01:10:37.000 --> 01:10:39.000 Yeah. 01:10:39.000 --> 01:10:42.000 So just be mindful of that 01:10:42.000 --> 01:10:43.000 from a design standpoint. 01:10:43.000 --> 01:10:44.000 That on the exam, 01:10:44.000 --> 01:10:45.000 if they're asking you, 01:10:45.000 --> 01:10:49.000 what is the architecture for OSPF? 01:10:49.000 --> 01:10:51.000 What does that look like to you, folks? 01:10:51.000 --> 01:10:53.000 What does this look like to you? 01:11:06.000 --> 01:11:07.000 Hub and spoke. 01:11:07.000 --> 01:11:09.000 That's what it looks like. 01:11:09.000 --> 01:11:10.000 Or star. 01:11:10.000 --> 01:11:11.000 Yeah. 01:11:11.000 --> 01:11:12.000 Hub and spoke or star. 01:11:12.000 --> 01:11:13.000 Exactly. 01:11:13.000 --> 01:11:15.000 So if you ever asked that question on an exam, 01:11:15.000 --> 01:11:16.000 hub and spoke or star 01:11:16.000 --> 01:11:19.000 is the configuration you try to achieve 01:11:19.000 --> 01:11:23.000 with something like OSPF. 01:11:23.000 --> 01:11:24.000 Right now, 01:11:24.000 --> 01:11:25.000 I often have people asking me, 01:11:25.000 --> 01:11:26.000 okay, 01:11:26.000 --> 01:11:27.000 now how can you relate this 01:11:27.000 --> 01:11:28.000 to like my real world environment? 01:11:28.000 --> 01:11:29.000 Raymond, 01:11:29.000 --> 01:11:30.000 please give me something more concrete than this. 01:11:30.000 --> 01:11:31.000 Sure. 01:11:31.000 --> 01:11:32.000 You know what? 01:11:32.000 --> 01:11:33.000 Let's say this is the core of your network. 01:11:33.000 --> 01:11:34.000 And this could be like, 01:11:34.000 --> 01:11:35.000 you know, 01:11:35.000 --> 01:11:36.000 where end users live. 01:11:36.000 --> 01:11:37.000 This could be, 01:11:37.000 --> 01:11:38.000 for example, 01:11:38.000 --> 01:11:39.000 like your data center. 01:11:39.000 --> 01:11:42.000 This might be the edge going out to the internet 01:11:42.000 --> 01:11:44.000 or going out to VPN connections 01:11:44.000 --> 01:11:45.000 or stuff like that. 01:11:45.000 --> 01:11:46.000 Right. 01:11:46.000 --> 01:11:47.000 Basically, 01:11:47.000 --> 01:11:48.000 just compartmentalize up your router. 01:11:48.000 --> 01:11:49.000 Say, 01:11:49.000 --> 01:11:50.000 okay, 01:11:50.000 --> 01:11:51.000 you know, 01:11:51.000 --> 01:11:52.000 if something happens right here in the environment, 01:11:52.000 --> 01:11:53.000 I only want it to affect those routers. 01:11:53.000 --> 01:11:54.000 You can even have your branch offices, 01:11:54.000 --> 01:11:55.000 your branch offices, 01:11:55.000 --> 01:11:57.000 your remote offices over your WAN connections, 01:11:57.000 --> 01:11:59.000 each in their own area. 01:11:59.000 --> 01:12:02.000 So a lot of different ways you can do this, 01:12:02.000 --> 01:12:04.000 as long as you're connecting everything right back up 01:12:04.000 --> 01:12:05.000 to area zero at headquarters. 01:12:05.000 --> 01:12:07.000 So headquarters might be that. 01:12:07.000 --> 01:12:09.000 I've seen people with DMVPNs. 01:12:09.000 --> 01:12:11.000 How many of you have played around with DMVPNs? 01:12:11.000 --> 01:12:12.000 If you have, 01:12:12.000 --> 01:12:13.000 then with a DMVPN, 01:12:13.000 --> 01:12:16.000 actually having the DMVPN as area zero 01:12:16.000 --> 01:12:18.000 and then headquarters as an area 01:12:18.000 --> 01:12:21.000 and all your different branches as areas as well. 01:12:21.000 --> 01:12:22.000 I mean, 01:12:22.000 --> 01:12:24.000 like there's no right or wrong way to do it. 01:12:24.000 --> 01:12:27.000 As long as it's the right way for you to do it, 01:12:27.000 --> 01:12:29.000 to get the results you want 01:12:29.000 --> 01:12:31.000 using the best practice design guidelines 01:12:31.000 --> 01:12:32.000 that you possibly can. 01:12:32.000 --> 01:12:34.000 And you're not going to be tested on design, 01:12:34.000 --> 01:12:35.000 though, 01:12:35.000 --> 01:12:36.000 for the exam, 01:12:36.000 --> 01:12:37.000 thank goodness, 01:12:37.000 --> 01:12:38.000 except for the fact, 01:12:38.000 --> 01:12:39.000 knowing that multi-area is all about what? 01:12:39.000 --> 01:12:40.000 Scalability, 01:12:40.000 --> 01:12:41.000 compartmentalization, 01:12:41.000 --> 01:12:42.000 isolation. 01:12:42.000 --> 01:12:43.000 What happens in Vegas stays in Vegas, 01:12:43.000 --> 01:12:44.000 I believe, 01:12:44.000 --> 01:12:45.000 as one of you said a little earlier, 01:12:45.000 --> 01:12:47.000 or what went in Rome stays in Rome, 01:12:47.000 --> 01:12:48.000 okay? 01:12:48.000 --> 01:12:49.000 What happens in Vegas stays in Vegas, 01:12:49.000 --> 01:12:50.000 stuff like that. 01:12:50.000 --> 01:12:51.000 And the last thing we want to cover 01:12:51.000 --> 01:12:53.000 before we wrap all of this up today 01:12:53.000 --> 01:12:55.000 is our router types. 01:12:55.000 --> 01:12:58.000 Backbone router versus internal router 01:12:58.000 --> 01:13:00.000 versus area border router 01:13:00.000 --> 01:13:02.000 versus ASBR. 01:13:02.000 --> 01:13:03.000 Okay, 01:13:03.000 --> 01:13:04.000 so backbone router, 01:13:04.000 --> 01:13:05.000 first and foremost, 01:13:05.000 --> 01:13:07.000 that is any router that's in the backbone. 01:13:07.000 --> 01:13:08.000 So remember, 01:13:08.000 --> 01:13:10.000 area zero is the backbone. 01:13:12.000 --> 01:13:14.000 And so any router that's in area zero 01:13:14.000 --> 01:13:15.000 is a backbone router. 01:13:15.000 --> 01:13:16.000 So backbone, backbone, backbone, backbone. 01:13:16.000 --> 01:13:17.000 Now, 01:13:17.000 --> 01:13:18.000 some people say, 01:13:18.000 --> 01:13:19.000 well, 01:13:19.000 --> 01:13:21.000 your area border router is also in your backbone, 01:13:21.000 --> 01:13:22.000 so technically it's a backbone router. 01:13:22.000 --> 01:13:23.000 Yeah, 01:13:23.000 --> 01:13:24.000 you know what? 01:13:24.000 --> 01:13:25.000 It technically is 01:13:25.000 --> 01:13:27.000 because it has its interface in area zero. 01:13:27.000 --> 01:13:29.000 So this would be an area border router here. 01:13:30.000 --> 01:13:31.000 Right? 01:13:31.000 --> 01:13:32.000 Its interface is in area zero. 01:13:32.000 --> 01:13:33.000 Area border router, 01:13:33.000 --> 01:13:34.000 its interface is area zero. 01:13:34.000 --> 01:13:36.000 What does an area border router do? 01:13:36.000 --> 01:13:38.000 An area border router connects you to area zero. 01:13:38.000 --> 01:13:39.000 That's what it does. 01:13:39.000 --> 01:13:41.000 So a lot of people say it's backbone router, 01:13:41.000 --> 01:13:43.000 and that's why you see here a backbone router, 01:13:43.000 --> 01:13:45.000 a router with at least one interface in area zero, 01:13:45.000 --> 01:13:46.000 right? 01:13:46.000 --> 01:13:47.000 But in reality, 01:13:47.000 --> 01:13:49.000 your backbone router is any router in area zero, 01:13:49.000 --> 01:13:50.000 period, 01:13:50.000 --> 01:13:51.000 okay? 01:13:51.000 --> 01:13:52.000 Keep that in mind for the exam. 01:13:52.000 --> 01:13:53.000 Now, 01:13:53.000 --> 01:13:54.000 the area border router, 01:13:54.000 --> 01:13:55.000 let's skip down to that one. 01:13:55.000 --> 01:13:56.000 See, 01:13:56.000 --> 01:13:57.000 that has at least one interface in area zero, 01:13:57.000 --> 01:13:59.000 and any other interface in any other area, 01:13:59.000 --> 01:14:01.000 and that's what I have here. 01:14:01.000 --> 01:14:02.000 I have this in area zero. 01:14:02.000 --> 01:14:03.000 I have this in area one. 01:14:03.000 --> 01:14:04.000 I have this in area zero. 01:14:04.000 --> 01:14:05.000 I have this in area 51. 01:14:05.000 --> 01:14:06.000 I have this in area zero. 01:14:06.000 --> 01:14:07.000 I have this in area 51, 01:14:07.000 --> 01:14:08.000 right? 01:14:08.000 --> 01:14:10.000 Those would be your area border routers. 01:14:10.000 --> 01:14:13.000 They are connecting area zero to some other area, 01:14:13.000 --> 01:14:16.000 and so we'll show you how to configure those tomorrow. 01:14:16.000 --> 01:14:18.000 You have your internal router. 01:14:18.000 --> 01:14:22.000 This is going to be a router that has all of its interfaces in some other area. 01:14:22.000 --> 01:14:23.000 So, 01:14:23.000 --> 01:14:24.000 for example, 01:14:24.000 --> 01:14:26.000 all of this router's interfaces are in area seven, 01:14:26.000 --> 01:14:27.000 so, 01:14:27.000 --> 01:14:28.000 therefore, 01:14:28.000 --> 01:14:29.000 it's an internal router. 01:14:29.000 --> 01:14:31.000 All of this router's interfaces are in area 51, 01:14:31.000 --> 01:14:32.000 therefore, 01:14:32.000 --> 01:14:33.000 it's an internal router. 01:14:33.000 --> 01:14:34.000 Same thing with this one, 01:14:34.000 --> 01:14:35.000 internal router, 01:14:35.000 --> 01:14:36.000 internal router. 01:14:36.000 --> 01:14:37.000 This is internal. 01:14:37.000 --> 01:14:38.000 This is internal. 01:14:38.000 --> 01:14:39.000 Internal routers. 01:14:39.000 --> 01:14:41.000 And then you have your autonomous system boundary router. 01:14:41.000 --> 01:14:42.000 So, 01:14:42.000 --> 01:14:45.000 this has at least one interface in any area, 01:14:45.000 --> 01:14:48.000 and another interface connected to a different routing domain. 01:14:48.000 --> 01:14:49.000 So, 01:14:49.000 --> 01:14:52.000 this would be an example of my autonomous system boundary router. 01:14:52.000 --> 01:14:53.000 So, 01:14:53.000 --> 01:14:54.000 an ASBR could be part of area zero. 01:14:54.000 --> 01:14:55.000 It could be part of any other area. 01:14:55.000 --> 01:14:56.000 It doesn't matter. 01:14:56.000 --> 01:14:59.000 As long as it has one interface in any of your areas, 01:14:59.000 --> 01:15:03.000 and then another interface connecting to something totally different than OSPF, 01:15:03.000 --> 01:15:05.000 then you are an ASBR. 01:15:05.000 --> 01:15:06.000 So, 01:15:06.000 --> 01:15:08.000 how can I actually turn a router into an ASBR? 01:15:08.000 --> 01:15:09.000 It's actually pretty simple. 01:15:09.000 --> 01:15:10.000 One, 01:15:10.000 --> 01:15:11.000 we could use, 01:15:11.000 --> 01:15:12.000 on this router, 01:15:12.000 --> 01:15:13.000 let's say we were using default routing. 01:15:13.000 --> 01:15:15.000 Let's say this is the internet. 01:15:15.000 --> 01:15:16.000 If that's the internet, 01:15:16.000 --> 01:15:23.000 then I might inject the default route into OSPF. 01:15:23.000 --> 01:15:24.000 So, 01:15:24.000 --> 01:15:26.000 if I inject the default route into OSPF with, 01:15:26.000 --> 01:15:27.000 yeah, 01:15:27.000 --> 01:15:29.000 default information originate is the command to do that. 01:15:29.000 --> 01:15:31.000 If I inject the default route into OSPF, 01:15:31.000 --> 01:15:34.000 that automatically makes me an ASBR. 01:15:34.000 --> 01:15:36.000 Automatically. 01:15:36.000 --> 01:15:37.000 So, 01:15:37.000 --> 01:15:39.000 it's not like I have to type in some special thing that says, 01:15:39.000 --> 01:15:40.000 you are an ASBR. 01:15:40.000 --> 01:15:41.000 No, 01:15:41.000 --> 01:15:42.000 just inject the default route. 01:15:42.000 --> 01:15:43.000 Why? 01:15:43.000 --> 01:15:47.000 Because that connects me to other routing domains at that point in time. 01:15:47.000 --> 01:15:52.000 Let's say instead that this was all EIGRP. 01:15:52.000 --> 01:15:57.000 And I wanted to redistribute EIGRP in the OSPF 01:15:57.000 --> 01:16:00.000 and redistribute OSPF in the EIGRP. 01:16:00.000 --> 01:16:01.000 Well, 01:16:01.000 --> 01:16:02.000 how do I do that? 01:16:02.000 --> 01:16:08.000 I would do that with the redistribution commands. 01:16:08.000 --> 01:16:10.000 Perform redistribution. 01:16:10.000 --> 01:16:14.000 That automatically turns me into an ASBR. 01:16:14.000 --> 01:16:15.000 So, 01:16:15.000 --> 01:16:16.000 how do you turn yourself into an ASBR? 01:16:16.000 --> 01:16:17.000 Easy. 01:16:17.000 --> 01:16:19.000 Inject default routes into OSPF on that router, 01:16:19.000 --> 01:16:21.000 do redistribution on that router, 01:16:21.000 --> 01:16:24.000 and you become an ASBR automatically. 01:16:24.000 --> 01:16:25.000 So, 01:16:25.000 --> 01:16:26.000 we'll see that as well in this course. 01:16:26.000 --> 01:16:27.000 So, 01:16:27.000 --> 01:16:28.000 we'll see backbone routers, 01:16:28.000 --> 01:16:29.000 ABRs, 01:16:29.000 --> 01:16:30.000 ASBRs. 01:16:30.000 --> 01:16:38.000 We'll show you how all that works here when we get to configuration and verification. 01:16:38.000 --> 01:16:39.000 So, 01:16:39.000 --> 01:16:40.000 a lot of great information there, 01:16:40.000 --> 01:16:41.000 folks, 01:16:41.000 --> 01:16:42.000 to help you get ready for the certification exam. 01:16:42.000 --> 01:16:44.000 Don't overlook any of that information. 01:16:44.000 --> 01:16:45.000 Why? 01:16:45.000 --> 01:16:46.000 Because you never know. 01:16:46.000 --> 01:16:51.000 One or two or three questions that require you to know what we've covered up to this point in time. 01:16:51.000 --> 01:16:55.000 You'd hate to not know that information and then not be able to complete that question.