Implementing Cisco IP Routing (642-902 ROUTE) Tutorials
Advanced OSPF / Lab 3 - Totally Stubby Areas
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Subtitles of the Movie (Implementing Cisco IP Routing (642-902 ROUTE) / Advanced OSPF / Lab 3 - Totally Stubby Areas)
So welcome back into our discussion of OSPF Areas. We're in the lab and we have configured Area 2 over here, Boston and the East Router, we've configured Area 2 as a Stub Area. So now we're going to configure a Totally Stubby Area and the Totally Stubby Area we're going to pick is Area 1. It's only got the one router in it and makes it a little easier for configuration if I don't have to configure it on East Poddunk as well even though that guy's not configured yet. But so let's go over here to West and the command to configure it as a Totally Stubby Area is pretty much the same as the, the Stub Area. You just have to add a Command Line argument to the Stub Command. So Config T, Router OSPF 1, we'll do Area 1, Stub and No Summary. It says do not send Summary LSAs into the Stub Area. So we'll No Summary and we'll exit this. Of course that tears down the adjacency because the Stub Flag no longer matches between West and San Diego so we'll go over to San Diego, Config T, Router whoops, Router OSPF 1, Area 1, Stub No Summary. Now we don't have to specify the No Summary argument here on the Area Routers, you only have to specify the No Summary on the Area Border Routers. I did it here just to show you that it doesn't cause an error but I could have just done Area 1 Stub and that makes the Stub Flag match. The only router that cares whether or not it has a Summary Route is the West Router, because the West Router is the Area Border Router. So now that the adjacency's come back up, we've exchanged routes, we'll look at the Routing Table here on West. Of course, we don't expect it to be changed at all, because it is an Area Border Router, it has to know all about all the routes. However let's go over here and look at San Diego. If we exit out of this guy and we do Show IP Route you'll notice that it's Routing Table is tiny compared to all the rest of them. It knows about it's directly connected networks, it knows about the networks that's in it's area which are two Loopback Interfaces that are off, of the West Router. Everything else it says, hey if you don't know where to send the data, send it to me and I'll get it where it needs to go. So the Area Border Router, this 192.168.10.1 is saying I have the routes to the rest of the network and if you look at the diagram, it does. San Diego can't get anywhere without going through West. If it wants to get to Boston, it has to go through West anyway so why bother advertising all of these routes back down into San Diego? Again it filters out the Type three, four and five LSAs from San Diego. So San Diego says, you know, I have a Default Route and this honestly, is the most common configuration when you're setting Stub Areas. If you're setting up a Totally Stubby Area, the understanding is, that all the routers in that area know how to get one another but that's all they need to know. Again this could be an OSPF area that is at a corporate headquarters building that is separate from your main corporate headquarters. You know, if you have a, a regional headquarters in Texas, obviously the networks in that building, the routers in that building need to know how to get to all of networks in that building, everything else is across a DS3 or an OC 12 or whatever type of WAN link you have back to your corporate office. So now we as network engineers have said, well this is what I really wanted. I wanted it to be a Totally Stubby Area. Stub Area really doesn't do anything for me because I'm still passing all these routes back and forth. So let's go make Area 2 a Totally Stubby Area as well, since again Boston can't get anywhere going through East Poddunk and it's got to go up through East and up to Chicago. So just to prove that you don't have to change that No Summary Flag on the member routers, we'll go over to the East and we'll just do, Config T, we'll do Router OSPF 1, we'll do Area 2, Stub, No Summary. We'll give it just a second and if we now go to Boston, we do a Show IP Route on Boston, we know about the connected areas, the networks in the area and we now just have a Default Route to get out everywhere else and this is exactly what we wanted Boston to do in the first place. And yeah, I, I know I took through the Stub Area just to show you the difference in the two. Of course, up here at Chicago, his Route Table is still huge because we're not doing any Summarization at the Area Border Routers which I've built the network so we can do Summarization and we will do Summarization here in one of the future videos. But for now San Diego and Boston are both in Totally Stubby Areas and we're going to move onto to talk about Virtual Links in the next video.
Tutorial Information
| Course: | Implementing Cisco IP Routing (642-902 ROUTE) |
| Author: | Greg Dickinson |
| SKU: | 34291 |
| ISBN: | 978-1-61866-028-2 |
| Release Date: | 2011-12-28 |
| Duration: | 10 hrs / 105 lessons |
| Work Files: |
Yes |
| Captions: | No |
| Compatibility: |
Vista/XP/2000, OS X, Linux QuickTime 7, Flash 8 |
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