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Implementing Cisco IP Routing (642-902 ROUTE) Tutorials
BGP / Lab - eBGP Configuration pt. 2
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Subtitles of the Movie (Implementing Cisco IP Routing (642-902 ROUTE) / BGP / Lab - eBGP Configuration pt. 2)
So we're continuing on with our basic configuration of BGP and we've looked at the Auto Summary Command and the next command that we're going to use, at least in the near term for setting up BGP is the Neighbor Command. Now if we just type Neighbor and hit Question Mark, we can specify the IP address or a Tag for the neighbor. Most of the time you're going to specify an IP address. In this case, our neighbor's IP address is 50.1.1.2. So we'll do Neighbor 50. 50.1.1.2 and if we hit Question Mark there, you see we have more commands for the neighbor than we do just for BGP itself. You can specify the Multihop, Next Hop Self, Next Hop Unchanged. We're going to look at a fair number of these as we go through this entire lab. For the time being though, the only one we're really worried about is the Remote AS and that's where you tell BGP this neighbor is in this Autonomous System. In this case, it's Autonomous System 12 so we'll do Remote AS 12. You can also specify the NL RI type. Since they're all Cisco Routers, don't really need to specify that on the Command Line. You hit Enter and there you go. Now you have a BGP Neighbor set up. Now since BGP requires configuration on both ends, if we do Show IP BGP Summary, we'll see that there's our Neighbor Statement, it's running version 4 on this. It shows we've received, sent nothing. It shows all zeros, it's never come up and it's state is Active. And if you'll recall from our discussion of EIGRP, if a Neighbor is in Active State, that means it is actively looking for the other neighbor. I'm sending packets to this guy, this 50.1.1.2, he's just not understanding me, he's not talking my language, he's not doing anything. And of course the obvious reason for that in our case, is that we haven't configured the other Router to look for packets, look for another neighbor. So let's go into our Access 1 Router and let's set up the BGP Neighbor to point to the ISP 1. So we'll open the Console here, Enable Mode, Configure T, Router BGP, in this case we are in Autonomous System 12, so we'll do Router BGP 12. We'll do Neighbor and let's verify the IP address. 50.1.1.1 is our neighbor in this case. So Neighbor 50.1.1.1, Remote AS will be 127. So now if we're on Access 1 and we Show IP BGP Summary, we see that the Neighbor State is Idle unlike the other Router where it's Active, Idle means I'm waiting to actually try to contact this guy and again, if you'll remember BGP is a very slow protocol to converge and there we go. Neighbor 50.1.1.1 is up. You didn't see it, but I actually had to pause the video there for a second, so it actually took about 30 or 40 seconds for the Neighbor adjacency to come up. Again that's very different from OSPF or EIGRP or any of our other IGPs. If we set up neighbors and the neighbor adjacency doesn't come up in about five or ten seconds, then we're going through Debugs and Pinging and everything else. In this case, BGP is one of those protocols that you just kind of have to wait on it. So now if we do Show IP BGP Summary, we see that the neighbor's been up for 33 seconds, we've sent and received messages. His AS is 127 and we've received no prefixes from this BGP Neighbor. And this Prefix Received is how many routes we're getting from the neighbor. And again, another difference between IGPs and BGP is you can have a Neighbor adjacency established but not actually trade any routes back and forth. Again, if you'll recall, if we set up an OSPF Neighbor and again you have to put the Network Command in there, just like you have to with BGP but if you have a Neighbor adjacency established, then that means you are actively trading that network back and forth. So you'd at least see the network between you and your neighbor in the Routing Table. Well if we do Show IP Route on the Access 1, we see a bunch of OSPF routes that are coming from our Core 1 Router but we don't see any BGP routes from the ISP Router. If you look on the Router on the other end, we'll do Show IP Route, we notice that we don't see those OSPF routes from the Access Router that the Access Router knows about on our ISP Router. And again if we do Show IP BGP Summary on this guy it's sees the neighbor, it's up, it's Autonomous System is 12. It's been up for two minutes and twenty seconds and we've received no prefixes from this guy either. So the Neighbor adjacency is up but we're not trading any routes back and forth. Now what we've just set up is called EBGP it's External BGP and what EBGP means is that the two neighbors that have formed an adjacency are in two different Autonomous Systems. Again you'll see that Autonomous System 12 and 127, the neighbors here are obviously not in the same system. Now what we're about to set up in the next video is what's called IBGP, it's Internal BGP and that's going to be BGP session between Access 1 and Access 2. And from a configuration standpoint it's set up pretty much the same way. However, there are some caveats when you're running IBGP that you have to look out for and it has to do with Next Hops and Route Redistribution and everything like that. So let's go to the next video, we'll pause this here and go onto the next video and we'll set up IBGP between Access 1 and Access 2 and then we'll Redistribute the networks from ISP 1 into the Access 1 and Access 2 Routers and see how that flows.
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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