So we've talked about OSPF Areas and Area Types and LSAs and Virtual Links and now here's the lab. Lab three, where we get to put it all together and see it in action. This is the best way that I learned. I really can't learn all that well from just reading a book although that does help, you got to do that, but I'm the kind of person that I have to put it all together and, and put in a lab and break it and fix it and try to make it do weird things and well, that's where I come up with some of these labs. So here's the labs that I've set up. This is available as part of the Work Files with the course. Everything in this network is already set up, all the Point-to-Point links are set up, OSPF is set up with these areas with the exception of the East Poddunk Router and this Area 3 down here. East Poddunk is not participating at all, in fact if we were to go to East Poddunk and look at it's Routing Table, you see it only knows about it's connected networks and, and that's it. It's not participating even, even as a Area Router in Area 2. Just for the ease of configuration. Now we will eventually configure it when we talk about Virtual Links but for the time being let's just concentrate on getting these two areas set up like we want them set up. So right now we have OSPF standard area set up for Area 1 and Area 2 and, and of course Area 0, the backbone area. And that means that if we were go to for example, Boston and we were to look at his Routing Table. Boston's Routing Table is huge. We've got all of our Inter Area and Intra Area routes here. We also have four External Routes that are being Redistributed into OSPF through the Chicago Router. I've got some Loopbacks set up on Chicago and I got some basic Redistribution going on. I know we haven't talked about Redistribution yet but it's, it's fairly simple, at least once you know all the ins and outs of it, but I've basically got four Loopbacks advertised into RIP and then I've got that RIP Redistributed into OSPF, just so we can see these External Networks here. Now we want to systematically reduce the size of the Routing Tables on these routers. For example Boston and San Diego really, there's only one way for them to ever get out, you know, they can't go through East Poddunk. Really the only way to get out of the network is to go through the West or the East Routers up to Chicago and then of course Chicago virtually has a, a connection out to you know, another area, another WAN link or however it's got to be done. And what you're seeing in the Routing Table is the result of a standard OSPF Area Configuration. None of the routes are summarized, none of the routes are filtered, all of the routers knows about all of the routes everywhere on the network. The only thing that's filtered out in the areas are the Type one and Type two LSAs so that you don't get those Router and DR and BDR Advertisements going into other areas. So how do we go about paring this down? First we're going to set up a Stub Area and we're going to set up Boston as the Stub Area. I'm just picking on Boston just because that's the router I happen to have up right now. And we're going to configure it in the hopes of getting rid of these E2 Type Routes and once we've configured it as a Stub Area, we'll still get all of these inside network routes but these four E2 Routes should go away and be replaced with a single default route that's being injected by the East Area Border Router. So let's get started. We'll start up here at the East since that's the top of our topology. We'll go into Config T, if I can type that is, I'm going to Router OSPF 1 and the command to set it up is Area 2 Stub and once you do that, since the Stub Flag has to match in the Hello packet and it will look for the adjacency to form, it tears down the adjacency. It says it's from Full to Down, Neighbor Down, Adjacency forced to Reset. If we wait long enough, if I talk long enough, Boston will eventually go down as well once the Dead Timer times out. And you notice the adjacency is not coming back up because the Stub Flag does not match. East says hey Area 2 is a Stub, Boston says well I don't have Area 2 as a Stub, I'm, I'm not going to form an adjacency with you. And eventually this adjacency will go down and all these routes will disappear from our Routing Table. And there it goes, the Dead Timers expired. We do Show IP Route now, you'll see we only know about the connected networks and that's it. We've just lost all routing here in Boston. So go into Config Mode, do the same command here, Router OSPF 1, Area 2 Stub and once you do that, Boston and East should reform their neighbor adjacency after just a few seconds and now it's formed the adjacency. If we look over here on East we see that it's gone from Loading to Full. So let's look at the Routing Table over here on East. Again we should not see any difference on the East Routing Table because it is an ABR so it has to know about all of these routes, so you'll see Gateway of Last Resort is not set. We've still got these four External Routes pointing back towards Chicago's Router, but if we look in Boston, we do Show IP Route, you'll notice that we do have a Gateway of Last Resort, 192.168.20.1 which is East's IP address in this network and you'll notice if we look through the Routing Table, we no longer have those External Routes, it's been replaced by this single default route down here. So basically what this is telling your router is, here's the routes to get to all of the networks that are in OSPF. Anything else you don't know about needs to come through me. It's injecting a Default Route back into Area 2. Let's go up here and look at Chicago. Chicago's Routing Table should not be changed whatsoever. It knows it about it's connected networks and it's not getting a Default Route from anywhere, nor is it receiving a Default or a Summary Route from any of the other ABRs yet. We will configure Summarization as we go through some of the Area Types. So now we've talked about the Standard and Stub Areas. In the next few videos, we're going to move on to some of the other type of OSPF areas, we'll configure them and show you what it does to the Routing Table.
|Course:||Implementing Cisco IP Routing (642-902 ROUTE)|
|Duration:||10 hrs / 105 lessons|
|Captions:||Available on CD and Online University|
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