So in this video we're going to start discussing Route Selection in BGP and more specifically how BGP selects it's routes and how we can influence that Route Selection decision using methods of our own making. Now between the last video and this one, I have gone into the Customer 1, the ISP 3 and the ISP 2 Router and I've finished configuring BGP using the commands that we've already gone over. Just the Router BGP and the Autonomous System, set up the Neighbors and I am advertising into BGP all of the networks at the customer site in this AS 55 and AS 50 as well as this WAN link that's down here between Customer 1 and ISP 3. And in doing this, I've introduced a few little issues, a few little quirks into our routing domain, our routing topology and as we go through correcting those little quirks and optimizing our network, we'll introduce you to the concepts that you'll need to succeed on the ROUTE exam. So you'll remember way back when we talked about the overview of BGP that BGP, if you don't tune it, acts exactly like RIP and what does RIP use for it's Metric or how does it determine what the best path through the network is? Well, it uses hop count. In this case, it uses hop counts for individual Routers, BGP, since it's a larger protocol, designed to scale more, it uses hop counts between Autonomous Systems. Now obviously under normal circumstances, we don't want to BGP to act like a glorified RIP. I mean if you can get it up and get it running and can get it configured and it'll work, but it obviously won't be optimized. If you're going to run BGP, if you're going to be responsible for the BGP Infrastructure for your environment, even if it's just connecting BGP to your Internet provider, then you really have to get down and dirty with BGP and tune it so that it runs in the most efficient manner possible to meet your business requirements. And I've designed this little simple network here to show you some of the basic pitfalls and to help you work through those pitfalls and hopefully learn a little bit in the process. So let's get started, let's take a little tour around our network and let's fix some of the little issues that's come up. So we'll start here at the Core 1 Router. We'll look at his Routing Table and Core 1 right now, is not participating in BGP at all. It only participates in OSPF. If we do Show IP Protocols you'll see that it's only using OSPF 1 and all of it's networks are directly connected. It's not learning anything through OSPF because no other Routers in it's routing domain are talking OSPF to him. We do have other Routers but they're advertising all of their networks via BGP. And in fact both of these Routers are Redistributing OSPF into BGP but not the other way around. Also this Core 1 Router as you'll remember has a Static Route to directly to Access 1 for any networks that's not in it's Local Routing Table. So basically, anything other than the 192.168.12 or these 10.20 networks that are the WAN links between the Core 1, the Access 1 and Access 2 Routers. So for the time being we can pretty much just ignore Core 1. We will come back to him because there's a little bit of an issue here and has to do with that Static Route and the more astute among you may have already figured out what the issue is, but don't, don't ruin for the rest of the class. Let's go over and look at Access 1. So if we look at Access 1, we do Show IP Route, we see that he's learning all kinds of routes through OSPF, BGP. There's connected, we don't have any Static Routes thank goodness, but we're learning a lot of routes through BGP for these networks that are elsewhere in the routing domain. The 151 the 150 and we've got some routes to the 50 networks up here as well. So we've got a few different numbers of networks and most of them are going through 10.20.2.2. 10.20.2.2 is the Access 2 Router. And for the most part these networks make sense to go through Access 2 from Access 1. If we look at 50.10 we'll see that the 50.10 network for example, it actually goes through 184.108.40.206 so it goes out through ISP 1. Look at 10.5, 10.5 also goes out through 220.127.116.11 so it goes out this way. Let's look at this 18.104.22.168 network down here. Now if we look at 22.214.171.124 it is going out through Access 2, well if we look at how our routing domain is set up, you can tell that even though you can get to those networks going through Access 2, it's obviously quicker for us to go from Access 1 to ISP 1 down to Customer 1 and then you're on the Router that has this network. Rather than going up through Core 1, down through Access 2, ISP 2, ISP 3. You've got more Routers in the path, so why did BGP pick Access 2? Well you'll recall that BGP uses Autonomous Systems, so if we go into Access 1, we do Show IP BGP, this actually shows us the BGP Routing Table and it tells us why BGP made the decisions that it did. If we look at it and follow the rules. So you may remember this slide from where we discussed BGP routing and this is the list that BGP goes through when it decides what networks get installed in the Routing Table. Now the networks that get installed in the Routing Table from the BGP Table are the networks with this little angle bracket here. You'll see that it says that's the best route. In this case there's really only one route to the 10.5.1 network, even though there's two Routers that advertise it. We'll, we'll get into that later. For the time being, we're going to concentrate on this 126.96.36.199 network and I'll hit Enter a couple of times just so that they're all on the screen together, they're not split up by this More. We'll examine how BGP sees this network and how to correct the Routing Deficiency 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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