[NOTE: Click the “DOWNLOAD” button to the right to download the free config files for this interactive lab]
Welcome to the CCDA Lab. We’ll be looking at some of the concentrations for a scalable OSPF design, including summarization and OSPF stop areas.
So, in this lab setup, we have three routers, R1, R2, R3. Now R2 is in boot area one and area zero, that means it’s in area [inaudible 00:00:19] router. R1 is completely in area one, and R3 would be redistributing some connected routes so it’s going to save as an ASPR
So let’s start with R1, actually let’s start with R3. So let’s take a look at the interfaces on this guy, so we have a lot of loopback interfaces, and then if we look at the OSPF configurations, so section router, network 192.168.0.0, which a wildcard mask of this would match zero to three, while the remainings are redistributed connected would match four and five, right? So if we were to check R1, show IP route, we’re going to see a couple of interesting routes there.
So the first one that we see is this intra-area route, so 2.2.2 is actually from R2, so let’s check this, so show, run section: router. Alright so we see that 2.2.2 is in Area 1, and of course also this one is in Area 1, but then this is in area 0.
Alright so if we come back to R1, we can also see that we have external routes, so that is the one that we redistributed into OSPF, so four and five, and the area of that theme is an inter area route. Cool, so that is what we have there.
Alright so let’s come to R3 and we’re going to talk about summarization. So remember with OSPF you can summarize either the ABS or the ASBFs. For the ASBFs you can summarize any of the routs that they are redistributing into OSPF. So come here and I’ll use the summary address command. So I want to summarize the four and five, so 192.168.4.0, and then I can specify the mask, so 255, I can use 254.0, you would cute out four and five. Alright so let’s see the change that that has done on R1. If I show IP routes, it’s not complete yet, let’s do it again, show IP route, alright so now it’s good.
So we have this summary route here, it’s just one external route now, its now 192.168.4.0, cool. So now if I come to R2, one thing I can do is to summarize all the other routes, so all these other routes here, I can summarize them to something. So let’s see, config+T, we go to router, OSPF 1, and I can use the area range command. Now since those routing area 0, we can use area 0 range and specify the IP address, so 192.168.0.0, since I want to do from 0 to 3, and then wildcard of the mask will 255.252.0. So if I were to check here now, R1, let’s just give it some time, show IP route, and then you can see that everything has been summarized. So while already looking at some of the benefits of summarization, you have smaller routes and tables, and basically just have more efficient routing.
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Now the final thing we can do is to make this particular area stub right, lets assume R1 is only going to anywhere through R2, so we can make this guy a stub router or a stub area. So I can come to router OSPF 1, and just say area 1 stub. Now all the routers in a particular area must agree on their stub setting, so I must also change it and R2, area 1 stub. Alright so what that is going to do is it’s going to remove this external route and replace it with a default route. So if I were to do a show IP route, I can see that I don’t have any external routes anymore, everything has been replaced with a default route to the area. I still have the inter area routes, and we can actually remove the inter area routes using the area 1 stub null summary. So we can make it a totally stubby area. So no summary, and then we’ll see what happens here. So basically these 2 routes would also be gone although we’ll still have our intra area routes. So we still have our intra area routes, but now every other route has been replaced with a default route. Nice!
So in this lab we’ve looked at how to do summarization built on the ASB routs, on the ASB routes, and how to use OSPF stub to reduce the routes in a particular area.