Implementing Cisco IP Routing (642-902 ROUTE) Tutorials
Basic OSPF / Lab 1 - Loopback Interfaces
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Subtitles of the Movie (Implementing Cisco IP Routing (642-902 ROUTE) / Basic OSPF / Lab 1 - Loopback Interfaces)
So we're continuing with our OSPF Lab. We've set up OSPF, we've got it running on all of our routers, now we're going to add our Loopback Interfaces into our routing process. So this is a very straightforward process, just as was to add the actual WAN interfaces and the LAN interfaces in. In this case we'll use the very general network commands, just so we can add all of these in, all at once and we'll do it on all five routers pretty quick. So here on corp it's 10.10.0, so Config T, Router OSPF One Network 10.10.0. 0.0.0.255.255 Area 0. You'll see we're still debugging here on the Corporate Router so we'll see all of these networks come in as we do these on the other routers. In this case, the Tennessee router is the 10.2.1 so Config T, Router OSPF One Network 10.2.0.0 0.0.255.255 Area 0. Again the same thing over here on Georgia. Config T Router OSPF One Network 10.1.0.0, there if I type the command right, I'm sure it works better. So we'll write this config out, do the same over here on sales. Router OSPF One, so there's our Configuration Commands on the Sales router and last but not least is engineering. That's 10.12 like so. And we'll go out and write this config as well. And so now let's go back over to corporate and look at our routing table over here. We'll write the config here just because I'm a little paranoid and don't want to lose all of my, all of my changes I've made. So now we do Show IP Route, let's look at all the networks we've learned. And look, we're learning all of these routes through OSPF but wait a minute, you'll notice that these routes are being advertised as slash 32 networks because they're loopback addresses and this is where I've eluded to the fact that loopback addresses are handled differently with OSPF. Just to verify, we'll go to one of these other routers, Tennessee for example, we'll do Show IP Interface Brief, think that'll tell me the subnet mask, no it won't. Do Show Interface Loopback 10 and you'll see that our Loopback Interfaces have a / 24 subnet mask but because they are Loopback it says hardware is loop back, OSPF sees those loopback addresses, well these are just loopbacks, they're not really going to have a network mask. So I'm going to advertise them as host routes. Now under most circumstances, that works pretty well, for the purposes of this lab, obviously we want to be able to route to the slash 24 network, just, you know in case, there happened to be something else on that loopback network. Not that there is, but this is also something important to remember if you have say MPLS networks and your loopback address is inside one of those MPLS networks. You know you'd have a, a slash 24 network and so you put your loopback as like the .250 address in that slash 24 network. Because OSPF sees that Loopback Interface as a Loopback Interface then you'll be advertising two networks back into the MPLS Cloud and back into OSPF. That can cause problems when you're advertising the same network using two subnet masks. You may have reachability problems. Luckily there is a way around this, you basically have to go into each of the Loopback Interfaces, for example, go here into the Tennessee, Config T, Interface Loopback 10 and you enter the command, IP OSPF Network Point-to-Point. That tells OSPF to advertise this network just as if it were a regular network instead of a loopback network. So we'll go here on loopback 11 and put the same command in there and now if we go back to our Corporate Router we should see slash 24 subnet mask for the 10.2 networks that we've learned through OSPF. So we'll do Show IP Route and like magic, 10.2.1.0 is now a slash 24, 10.2.2.0 slash 24 are now advertising with the correct subnet masks. The old networks have disappeared from our routing table and there replaced with the correct routes. Now I'm not going to bore you by going to the other four routers and changing all of the loopback addresses so we'll use the magic of nonlinear video editing and jump right to the point where all that is finished. And like magic we're done. You'll notice that here on our Corporate Router we now know about all of these subnets, the 10.1, 10.2, 10.11, 10.12 and they're all slash 24 networks. You notice that 10.0.0.0 slash 24 is subnetted with 14 subnets so that means that the slash 24 subnet mask applies to all of these routes. So now our OSPF routed network is up and fully running and in the last video for this lab, we will delve into Router IDs, Router priorities and Basic Router Troubleshooting. But for now, that concludes this section of the lab.
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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