So we're carrying on with our EIGRP Summarization Lab and I have gone and configured the IP Summarization or the Summary Networks on both the South and the West Routers as well. And now you'll notice that on the Central Routers, we're only getting five routes through EIGRP. The 10.10, 10.11, 10.2, 10.3 and then own Summary Route, this 10.1.0.0 and it's pointing at null zero. We're going to take a couple of minutes and explore this. Now why do we have a Summary Network route pointing at null zero here? Quite simply, it's so that if one of these smaller networks, the 10.1.7 network for example, if it goes down, we lose our route to it from the central network. However, since we're advertising this summary to this null interface we don't lose our Summary Route. For example, if the Summary Route was tied to the 10.1.7 this loopback 16 interface, and it goes down, then that route update will go out to all of the other routers on the network and then you'll start the hello process and it'll look for neighbors, the route will go active, all kinds of neat stuff starts happening because obviously no other routers have routes to this network. So here's the routing table on central, something else that you'll notice, let's look at the routing table on South for example. You'll notice that we are learning the Summary Routes to 10.2 and 10.3 even though these Summary Routes aren't configured on the interface that's pointing to South. You'll recall that the South and West networks are on a different Frame Relay interface than the North and East and that just shows you that the routes are being summarized here at these routers and being advertised over to central and central says, well I don't really know how East can get to these three networks or the route is actually for these four networks. I don't really care how East can get to these four networks, I just can and so I'm going to advertise that I know how to get all of these networks back to the West and the South. You notice that we are getting all of the individual routes for the 10.1 network because the Central Router knows about all of those and we're not summarizing those routes out to this side of the network, this 22.8 network. And so the South and the West Routers both are not getting this summary. Let's fix that. Obviously, we can summarize central, North and East into one big network summary on this .9 interface. We can summarize it as 10.0.0.0 with a 10.252.0.0 subnet mask. And this is getting overly broad, I mean, obviously we don't have all of those networks on this side of the network but you know this is a lab, this is obviously not something you put in production. You'd just summarize this 10.1 network here on central but let's see what happens if we have networks that are being summarized from East to North that are rolling up under a larger Summarization here at central. Let's just see what happens when we do that. So we'll go up to here central an we will do Show IP Interface Brief just to make sure we're on the right interface and the .9 address is on serial 0 slash 2.9. So we will go and do Config T and interface serial 0 slash 2.9. We'll do IP Summary Address 10.0.0.0 255.252.0.0. Did I forget something there? I think I got to put EIGRP in there somewhere. Yes I do, EIGRP 90, then 10.0.0.0 255.252.0.0 and hit Enter. Our neighbors go down and our neighbors will come back up in just a moment. So now both of our adjacencies are up from central, so let's look out here at South, do a Show IP Route here and you'll notice that our routing table has shrunk dramatically. We now know about this entire slash 14 network going through this .9 address. So as you can see the router's intelligent enough to handle this Summarization, let's just make sure that it actually works. So if we go on this router and we do ping 10.2.1.1 which is the loopback address on the North Router, we have success, so we're going from the South to the North through this Summary Route on the central and it just works even though some people might have trouble wrapping their minds around it and in fact I did. Well, you know, hey wait a minute, you're summarizing Summary Routes that, that doesn't work you know? For some reason, a lot of people think that they don't work and, and they absolutely do as you can see here in the, the lab that we've just done. So as you see Summarization can be a very powerful tool to allow you to reduce the size of your routing table, reduce the overhead, reduce the load of your routers but like with many tools with great power comes great responsibility and if you summarize too much, then you'll have packets flying all around your network in a big circle you know, life just 00:05:18 ] won't be happy at all for you as a network administrator or a network engineer. And that concludes this section of our lab. In the next section of our lab, we'll talk about configuring the Central Router to use more bandwidth for it's EIGRP updates and how a question that's worded like this, is actually somewhat a trick question. So we'll study that in the next video.
|Course:||Implementing Cisco IP Routing (642-902 ROUTE)|
|Duration:||10 hrs / 105 lessons|
|Captions:||Available on CD and Online University|
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