WEBVTT 00:00:01.000 --> 00:00:06.000 So now folks, we're going to dive into a discussion on manipulating BGP best path selection process. 00:00:06.000 --> 00:00:09.000 This is not an official exam objective. 00:00:09.000 --> 00:00:23.000 However, you know, sometimes when I take exams, I potentially experience things that were never introduced to us in the actual exam objective outline. 00:00:23.000 --> 00:00:25.000 It happens quite often. 00:00:26.000 --> 00:00:36.000 So being instructor is my duty to ensure that you are all prepared for the possibility of things creeping up on your certification exam, 00:00:36.000 --> 00:00:44.000 whether it's something that's going to be officially tested on or not based on the official exam objectives. 00:00:44.000 --> 00:00:48.000 So with that said, we need to talk about manipulating BGP best path selection process, 00:00:48.000 --> 00:00:54.000 something that I never did for version 1.0, but I do for version 1.1 now that's not actually in the exam objectives. 00:00:54.000 --> 00:00:58.000 But here we go. Let's talk about four of those attributes. 00:00:58.000 --> 00:01:04.000 And so what I've had to do here is I've had to reconfigure my environment during break really, really, really, really, really fast. 00:01:04.000 --> 00:01:07.000 So what do we have right now? 00:01:07.000 --> 00:01:11.000 We have an E-BGP session here. 00:01:11.000 --> 00:01:15.000 We have an I-BGP session here now. 00:01:15.000 --> 00:01:21.000 We have two, two E-BGP sessions here. 00:01:21.000 --> 00:01:24.000 We have an E-BGP session here. 00:01:24.000 --> 00:01:29.000 And we have an E-BGP session here. 00:01:29.000 --> 00:01:38.000 In addition to that down here, I have the network 192.192.192.192 for fun. 00:01:38.000 --> 00:01:48.000 And we are going to go through a lot of our, we're going to go through four of our attributes. 00:01:48.000 --> 00:01:59.000 Specifically, we'll talk about here weight, local preference, AS path, and MED to help us understand the importance of these four 00:01:59.000 --> 00:02:06.000 when it comes to influencing routes in our particular environment. 00:02:06.000 --> 00:02:09.000 So let's begin here with a discussion on weight. 00:02:10.000 --> 00:02:14.000 So weight, as I mentioned, is Cisco proprietary. 00:02:14.000 --> 00:02:19.000 Meaning it's also, and it's also locally significant to the router. 00:02:19.000 --> 00:02:31.000 Meaning that when you manipulate weight, you change weight, you adjust weight, it only affects that router that you're doing it on. 00:02:31.000 --> 00:02:37.000 It's an attribute that is not shared with any other router and any updates, no matter what. 00:02:37.000 --> 00:02:40.000 It's locally significant to the router. 00:02:40.000 --> 00:02:46.000 And so you can manipulate weight to influence the path leaving your autonomous system as an example. 00:02:46.000 --> 00:02:49.000 Or just changing your router's decision, right? 00:02:49.000 --> 00:02:51.000 It doesn't have to be leaving your autonomous system. 00:02:51.000 --> 00:02:53.000 It could be like, I want to go this way instead. 00:02:53.000 --> 00:02:57.000 And that might be to another router inside of your autonomous system that's running BGP. 00:02:57.000 --> 00:03:06.000 Whatever the reason is, or not whatever the reason, whatever you're trying to accomplish, it's based on the fact that you are trying to tell your router, 00:03:06.000 --> 00:03:10.000 I don't like the decision you've made based on whatever attribute you've made this decision on. 00:03:10.000 --> 00:03:11.000 And I want you to go the other way. 00:03:11.000 --> 00:03:13.000 I want you to go a different way. 00:03:13.000 --> 00:03:15.000 I want you to choose a different path. 00:03:15.000 --> 00:03:21.000 Specifically, I want you to use this path I'm telling you to use right now. 00:03:21.000 --> 00:03:24.000 Remember that higher is better for weight. 00:03:24.000 --> 00:03:28.000 If you learn it, you automatically get a value of zero for weight. 00:03:28.000 --> 00:03:32.000 If you locally generate a route, you get a weight of 32,768. 00:03:32.000 --> 00:03:38.000 So, if we look at our routers right here, you'll see that this router locally generated that network. 00:03:38.000 --> 00:03:45.000 It's the one that I use the network command on R1 to dump this into that table. 00:03:45.000 --> 00:03:51.000 And then we look down here, all the rest are zero because these are ones that we have learned. 00:03:51.000 --> 00:03:54.000 So, zero is the default for learned routes. 00:03:54.000 --> 00:03:59.000 32,768 is the default for routes that you've injected yourself. 00:03:59.000 --> 00:04:01.000 And remember, this is locally significant. 00:04:01.000 --> 00:04:04.000 BGP will not pass this information to other routers. 00:04:04.000 --> 00:04:06.000 So, there's two different ways we can do this. 00:04:06.000 --> 00:04:10.000 We can do this with a route map, and we can do these without a route map. 00:04:10.000 --> 00:04:14.000 So, let me just show you quickly first how to do it without a route map. 00:04:14.000 --> 00:04:23.000 Now, when you do it without a route map, you have to do it for essentially every single route you learn from a specific neighbor. 00:04:23.000 --> 00:04:33.000 So, for example, if I learn from this neighbor that I'm a neighbor with, I want everything I learn from them to have a weight of 40, as an example. 00:04:33.000 --> 00:04:36.000 So, when you don't use a route map, you don't have granular control. 00:04:36.000 --> 00:04:39.000 When you use a route map, you will have granular control. 00:04:39.000 --> 00:04:42.000 So, let me just show you this one without granular control right now. 00:04:42.000 --> 00:04:45.000 So, this is R1 in our environment. 00:04:45.000 --> 00:04:47.000 R1. 00:04:48.000 --> 00:04:50.000 This router right here. 00:04:53.000 --> 00:05:01.000 And when we look at this network right here, that network is down here. 00:05:01.000 --> 00:05:05.000 So, 192.192.192.192. 00:05:08.000 --> 00:05:11.000 Notice I've learned about it two different ways. 00:05:11.000 --> 00:05:24.000 I've learned about it from this neighbor, which is EBGP, and I've learned about it from this neighbor, which is IBGP. 00:05:41.000 --> 00:05:42.000 Okay. 00:05:42.000 --> 00:05:47.000 So, I'm going to show you one more thing before we get deeper into this. 00:05:47.000 --> 00:05:49.000 But you see this? 00:05:49.000 --> 00:05:51.000 You see that IP address? 00:05:51.000 --> 00:05:52.000 Okay, we're on R1 right now. 00:05:52.000 --> 00:05:53.000 Remember, we're on R1. 00:05:53.000 --> 00:05:55.000 You see that IP address? 00:05:55.000 --> 00:05:59.000 That's this router's IP address over here. 00:06:00.000 --> 00:06:21.000 When you learn a route via EBGP and you share with an IBGP neighbor, the next hop IP address is the IP address of the router in the next hop autonomous system. 00:06:21.000 --> 00:06:24.000 The router doesn't automatically update it. 00:06:24.000 --> 00:06:26.000 What does that mean? 00:06:27.000 --> 00:06:36.000 It means that this router has to know how to get to this next hop or else it can't use the route. 00:06:36.000 --> 00:06:40.000 Because remember the first rule, if you can't get to the next hop, ignore it. 00:06:40.000 --> 00:06:43.000 Notice how I am using it. 00:06:43.000 --> 00:06:47.000 It's the greater than sign, which means I can get to that next hop. 00:06:47.000 --> 00:06:50.000 Does anybody know why I can get to that next hop right now? 00:06:50.000 --> 00:06:51.000 Just think about it for a second. 00:06:51.000 --> 00:06:53.000 Why can I get to that next hop? 00:06:54.000 --> 00:07:01.000 What did we configure last week in this entire network, which is running underneath right now all of this? 00:07:13.000 --> 00:07:14.000 OSPF, right? 00:07:16.000 --> 00:07:18.000 It would be OSPF. 00:07:18.000 --> 00:07:19.000 Yeah. 00:07:20.000 --> 00:07:23.000 That's why right now I can get to that next hop. 00:07:23.000 --> 00:07:31.000 Now, if I wasn't running OSPF and I didn't learn about the OSPF, we would have to make sure we can learn about it somehow, either through a static route. 00:07:31.000 --> 00:07:33.000 Default routing can work as well for that. 00:07:33.000 --> 00:07:36.000 For the next hop, default routing works in your routing table. 00:07:36.000 --> 00:07:38.000 I need a route to get to that next hop. 00:07:39.000 --> 00:07:45.000 But there is a built-in BGP feature that is called next hop self. 00:07:45.000 --> 00:07:50.000 So, for example, right now we type in – we're using address families here, right? 00:07:50.000 --> 00:07:53.000 Address family IPv4 unicast on this router. 00:07:53.000 --> 00:08:10.000 If I type in neighbor 192.168.255.1 and I type in next hop self, then everything I share with R1 is going to have my IP address as the next hop. 00:08:10.000 --> 00:08:14.000 So, if we go back to R1 now, we should see that that has changed. 00:08:15.000 --> 00:08:21.000 And not yet. 00:08:21.000 --> 00:08:22.000 Why? 00:08:22.000 --> 00:08:23.000 Because BGP is slow. 00:08:23.000 --> 00:08:27.000 So, let's do do clear IP BGP star out. 00:08:27.000 --> 00:08:33.000 That's what we call a soft refresh, meaning I do not tear down my TCP session. 00:08:33.000 --> 00:08:37.000 All I do is send updates without resetting the neighbor adjacency. 00:08:37.000 --> 00:08:44.000 So, whenever you type an out or in, so outbound refresh or inbound refresh, then that is a soft reset. 00:08:44.000 --> 00:08:50.000 But if you leave out, out or in, then it resets the whole TCP session, which would have a ripple effect on the Internet, by the way. 00:08:50.000 --> 00:08:52.000 So, you typically want to avoid that. 00:08:52.000 --> 00:08:53.000 All right. 00:08:53.000 --> 00:08:56.000 Now you'll see that the next hop is R2. 00:08:56.000 --> 00:09:01.000 So, many different ways to get to the next hop. 00:09:01.000 --> 00:09:03.000 You can either do static routing. 00:09:03.000 --> 00:09:05.000 You could do default routing. 00:09:05.000 --> 00:09:11.000 You could advertise the route into OSPF like we had done in a previous session. 00:09:11.000 --> 00:09:17.000 Or you could just change the next hop so that way there the router in your environment makes itself the next hop. 00:09:17.000 --> 00:09:21.000 So, that way R1 knows how to get there and that one knows how to get there. 00:09:21.000 --> 00:09:23.000 That's just another option you have. 00:09:23.000 --> 00:09:24.000 All right. 00:09:24.000 --> 00:09:29.000 So, with that in mind, let's get back to our metric discussion. 00:09:29.000 --> 00:09:40.000 So, now we can see that we can either get to this network going through EBGP or we can get to this network going through IBGP. 00:09:40.000 --> 00:09:41.000 Now, remember what I said earlier. 00:09:41.000 --> 00:09:45.000 One of our attributes is prefer EBGP over IBGP. 00:09:45.000 --> 00:09:50.000 So, my question to you folks right now is why did we prefer IBGP over EBGP? 00:09:50.000 --> 00:10:05.000 Why did we prefer IBGP over EBGP in this scenario? 00:10:06.000 --> 00:10:12.000 Well, first of all, we didn't even get that far in our list. 00:10:12.000 --> 00:10:14.000 Why did we not get that far in our list? 00:10:14.000 --> 00:10:18.000 Well, if we look at our list again, I'll bring that up right here. 00:10:18.000 --> 00:10:21.000 Let's put that over my head. 00:10:21.000 --> 00:10:24.000 So, if we start off with metric, right? 00:10:24.000 --> 00:10:26.000 So, metric or sorry, weight. 00:10:26.000 --> 00:10:27.000 Start off with weight. 00:10:27.000 --> 00:10:28.000 Weight is tied. 00:10:28.000 --> 00:10:30.000 Then local preference is tied. 00:10:30.000 --> 00:10:33.000 Then it was not locally originated. 00:10:33.000 --> 00:10:34.000 So, that's tied. 00:10:34.000 --> 00:10:36.000 Then we have AS path. 00:10:36.000 --> 00:10:37.000 Shorter. 00:10:37.000 --> 00:10:38.000 Shorter AS path. 00:10:38.000 --> 00:10:39.000 There you go. 00:10:39.000 --> 00:10:40.000 Done. 00:10:40.000 --> 00:10:42.000 Shorter AS path is the reason why that one is being used. 00:10:42.000 --> 00:10:43.000 All right. 00:10:43.000 --> 00:10:49.000 So, now that we know that, we could manipulate weight or we can manipulate local preference 00:10:49.000 --> 00:10:52.000 and that would change this router's decision making process. 00:10:53.000 --> 00:10:58.000 So, what we're going to do is we are going to take. 00:10:58.000 --> 00:10:59.000 Yeah. 00:10:59.000 --> 00:11:00.000 Okay. 00:11:00.000 --> 00:11:01.000 We're back on the slide. 00:11:01.000 --> 00:11:08.000 What we're going to do is we are going to say that anything we learn from this EBGP neighbor, 00:11:08.000 --> 00:11:10.000 anything we learn from that neighbor. 00:11:10.000 --> 00:11:14.000 So, neighbor, 203011389. 00:11:14.000 --> 00:11:16.000 Anything we learn from that neighbor. 00:11:16.000 --> 00:11:21.000 So, neighbor, 203011389. 00:11:23.000 --> 00:11:24.000 I want. 00:11:30.000 --> 00:11:31.000 We are using address families here. 00:11:31.000 --> 00:11:33.000 So, I got to do address families. 00:11:37.000 --> 00:11:38.000 Yeah. 00:11:38.000 --> 00:11:39.000 I don't see it there. 00:11:39.000 --> 00:11:42.000 So, address family IPv4 unicast. 00:11:43.000 --> 00:11:44.000 It's going to be neighbor. 00:11:44.000 --> 00:11:46.000 Let's put that neighbor address back in. 00:11:46.000 --> 00:11:48.000 And then we can type in. 00:11:48.000 --> 00:11:50.000 We should see an option for weight in this output. 00:11:53.000 --> 00:11:54.000 There it is. 00:11:54.000 --> 00:11:55.000 Weight. 00:11:55.000 --> 00:11:57.000 And then let's set our weight. 00:11:57.000 --> 00:12:01.000 So, what is the current weight right now of these two paths we have? 00:12:01.000 --> 00:12:04.000 The two paths we have, the weight is zero and zero. 00:12:05.000 --> 00:12:06.000 So, if we. 00:12:07.000 --> 00:12:09.000 What higher weight is better? 00:12:09.000 --> 00:12:15.000 So, let's make anything we learn from that neighbor higher than zero. 00:12:15.000 --> 00:12:18.000 So, let's specify five as an example. 00:12:19.000 --> 00:12:24.000 And do clear IPBGP star in. 00:12:24.000 --> 00:12:27.000 So, let's refresh everything we've learned inbound from our neighbors. 00:12:27.000 --> 00:12:36.000 And what we should see now when we look at our table is that anything we learned from this router has now a weight of five. 00:12:37.000 --> 00:12:39.000 So, let's just focus now on this network here. 00:12:40.000 --> 00:12:45.000 And you'll see that we are now preferring this path right here. 00:12:46.000 --> 00:12:48.000 Why are we preferring this path? 00:12:49.000 --> 00:12:54.000 We're preferring this path because higher weight. 00:12:54.000 --> 00:12:55.000 That's it. 00:12:55.000 --> 00:12:56.000 Higher weight. 00:12:56.000 --> 00:13:03.000 So, now we're going to go this way to get to that network instead of this way to get to that network. 00:13:03.000 --> 00:13:08.000 So, we influence the individual router's decision-making process. 00:13:09.000 --> 00:13:17.000 Now, the problem with this, as I said, is that it affects every single network that we've learned from that device. 00:13:17.000 --> 00:13:19.000 Now, is that what we want? 00:13:19.000 --> 00:13:20.000 If it is, great. 00:13:20.000 --> 00:13:32.000 So, as you can see, if we wanted to make sure that this router, no matter what, for all internet destinations, chose this way instead of coming through this router, then that makes sense. 00:13:32.000 --> 00:13:33.000 That works. 00:13:33.000 --> 00:13:38.000 Everything we learned from that neighboring ISP router, I want to make sure we always go that way unless there's a failure. 00:13:38.000 --> 00:13:40.000 If it fails, then we can use the other path. 00:13:40.000 --> 00:13:41.000 Perfect. 00:13:41.000 --> 00:13:43.000 That's what this would accomplish for me. 00:13:44.000 --> 00:13:48.000 But what if there's only specific routes that you wanted to match? 00:13:48.000 --> 00:13:51.000 Well, that's where you're going to have to use something called a route map. 00:13:51.000 --> 00:13:53.000 So, let me erase this right now. 00:13:54.000 --> 00:13:56.000 We'll clear our BGP. 00:13:56.000 --> 00:14:01.000 Now, with a route map, we're going to have to specify which routes we want to match. 00:14:01.000 --> 00:14:02.000 So, what are we going to need? 00:14:02.000 --> 00:14:04.000 We're going to need, first of all, a prefix list. 00:14:04.000 --> 00:14:06.000 So, a prefix list to match that. 00:14:06.000 --> 00:14:10.000 So, IP prefix list BGP wait example. 00:14:11.000 --> 00:14:17.000 I'm going to call it prefix list underscore BGP WEIGHD. 00:14:18.000 --> 00:14:20.000 And then we are going to say that. 00:14:20.000 --> 00:14:21.000 What is my commands here? 00:14:21.000 --> 00:14:22.000 We're going to permit. 00:14:22.000 --> 00:14:25.000 So, I want to permit. 00:14:25.000 --> 00:14:26.000 What is it? 00:14:28.000 --> 00:14:30.000 It's going to be this one right here. 00:14:31.000 --> 00:14:33.000 So, I just want to match that one right there. 00:14:34.000 --> 00:14:35.000 That's it. 00:14:36.000 --> 00:14:38.000 Now, I don't have to worry about all the other traffic, 00:14:38.000 --> 00:14:40.000 because all the other traffic, all the other stuff, 00:14:40.000 --> 00:14:43.000 is going to be falling under my default route map after. 00:14:43.000 --> 00:14:46.000 So, I'm just going to specify what I want to match. 00:14:46.000 --> 00:14:48.000 I want to match this specific network ID. 00:14:49.000 --> 00:14:50.000 Now, we're going to create my route map. 00:14:51.000 --> 00:14:54.000 And so, my route map allows me to do a construct here 00:14:54.000 --> 00:14:59.000 that allows me to differentiate different types of traffic from other types of traffic. 00:14:59.000 --> 00:15:00.000 Or routes, I should say. 00:15:01.000 --> 00:15:02.000 Network IDs, different things like that. 00:15:03.000 --> 00:15:04.000 So, with route map, for example, 00:15:04.000 --> 00:15:10.000 I'm going to go ahead and call this one my route map underscore BGP WEIGHD. 00:15:10.000 --> 00:15:11.000 E-I-G-H-T. 00:15:12.000 --> 00:15:14.000 E-I-G-H-T. 00:15:14.000 --> 00:15:19.000 And then I'm going to say that this entry is going to be a permit. 00:15:20.000 --> 00:15:21.000 And I'm going to give it a sequence number of 10. 00:15:23.000 --> 00:15:28.000 So, now I want to match the IP prefix list we created earlier. 00:15:29.000 --> 00:15:32.000 Nope, it's got to be IP address prefix list. 00:15:33.000 --> 00:15:35.000 And what do we call our prefix list? 00:15:35.000 --> 00:15:36.000 I want to match this one right here. 00:15:37.000 --> 00:15:39.000 Now, I'm going to set. 00:15:39.000 --> 00:15:40.000 Set what? 00:15:40.000 --> 00:15:41.000 Set the weight. 00:15:41.000 --> 00:15:43.000 Set the weight to, let's say, 7. 00:15:44.000 --> 00:15:49.000 So, if you match this, if you're a network ID and you match this, 00:15:50.000 --> 00:15:52.000 your weight is now 7. 00:15:53.000 --> 00:15:57.000 Now, what we're going to do is we're going to create another sequence in this route map. 00:15:57.000 --> 00:15:59.000 So, think of it like an access control list. 00:16:00.000 --> 00:16:01.000 Sequence 10 is one entry. 00:16:02.000 --> 00:16:04.000 Sequence 20 is now a totally different entry. 00:16:06.000 --> 00:16:08.000 And I'm going to match everything else. 00:16:08.000 --> 00:16:09.000 Match everything else. 00:16:10.000 --> 00:16:11.000 So, what is everything else? 00:16:12.000 --> 00:16:13.000 Well, I just leave it blank. 00:16:13.000 --> 00:16:14.000 I don't put a match. 00:16:14.000 --> 00:16:19.000 And if I want to use the default weight, I just leave it blank as well. 00:16:19.000 --> 00:16:21.000 So, basically, leave the whole thing blank. 00:16:22.000 --> 00:16:27.000 This means permit everything else and use default values. 00:16:27.000 --> 00:16:28.000 That's what it means in this case. 00:16:29.000 --> 00:16:37.000 So, now, we go back into router BGP configuration mode for 65,001 on R1. 00:16:37.000 --> 00:16:41.000 And what we're going to do is we're now going to say under. 00:16:42.000 --> 00:16:43.000 Is it going to be address family configuration mode? 00:16:44.000 --> 00:16:45.000 Neighbor. 00:16:45.000 --> 00:16:47.000 So, neighbor what? 00:16:47.000 --> 00:16:49.000 So, when I am learning from this neighbor. 00:16:49.000 --> 00:16:50.000 Who is it? 00:16:50.000 --> 00:16:51.000 203011389. 00:16:53.000 --> 00:16:55.000 I want to apply. 00:16:58.000 --> 00:16:59.000 No, it is under address family. 00:17:00.000 --> 00:17:03.000 So, address family IPV4 Unicast. 00:17:03.000 --> 00:17:04.000 All right. 00:17:04.000 --> 00:17:05.000 So, when I'm learning from that neighbor. 00:17:09.000 --> 00:17:15.000 Then, we want to apply this route map that we created. 00:17:16.000 --> 00:17:20.000 And the route map we just created is called route map BGP weight. 00:17:21.000 --> 00:17:23.000 And we want to apply inbound. 00:17:24.000 --> 00:17:26.000 Inbound meaning when I'm learning from that neighbor. 00:17:26.000 --> 00:17:28.000 When I'm learning from that neighbor. 00:17:28.000 --> 00:17:29.000 All right. 00:17:29.000 --> 00:17:31.000 So, now, let's clear the BGP process. 00:17:35.000 --> 00:17:36.000 So, we can refresh everything. 00:17:36.000 --> 00:17:41.000 And what's going to happen now is that when I learn from that router. 00:17:43.000 --> 00:17:44.000 We are now going to apply this route map. 00:17:44.000 --> 00:17:47.000 And if we type in do show route-map. 00:17:47.000 --> 00:17:51.000 It states that when you match. 00:17:51.000 --> 00:17:52.000 So, this is a permit. 00:17:52.000 --> 00:17:53.000 Permit. 00:17:53.000 --> 00:17:55.000 When you match this prefix list. 00:17:55.000 --> 00:17:58.000 Which is 192.192.192.192. 00:17:58.000 --> 00:18:00.000 Then, go ahead and set the weight to 7. 00:18:01.000 --> 00:18:02.000 For everything else. 00:18:02.000 --> 00:18:04.000 Just leave it at its default values. 00:18:06.000 --> 00:18:09.000 Because there is an explicit deny or an implicit deny all. 00:18:09.000 --> 00:18:11.000 Just like an access control list or route map. 00:18:11.000 --> 00:18:12.000 So, if I did not include this. 00:18:12.000 --> 00:18:15.000 Then, everything else would not be learned. 00:18:15.000 --> 00:18:16.000 Right. 00:18:16.000 --> 00:18:17.000 You see what's happening there. 00:18:17.000 --> 00:18:18.000 So, I got to say permit. 00:18:18.000 --> 00:18:19.000 So, I learn it. 00:18:19.000 --> 00:18:20.000 Learn everything else. 00:18:20.000 --> 00:18:23.000 And set their default values to whatever they are. 00:18:23.000 --> 00:18:25.000 If I had a deny here. 00:18:25.000 --> 00:18:27.000 Then, it would mean do not learn everything else. 00:18:27.000 --> 00:18:29.000 So, that's why I have this catch all. 00:18:29.000 --> 00:18:30.000 It's like permit IP any, any. 00:18:30.000 --> 00:18:32.000 In an access control list. 00:18:33.000 --> 00:18:34.000 All right. 00:18:34.000 --> 00:18:35.000 So, now, that's cooked. 00:18:35.000 --> 00:18:36.000 Let's see. 00:18:36.000 --> 00:18:37.000 If we type in do show IP BGP. 00:18:37.000 --> 00:18:40.000 We should see that only one of them has been affected. 00:18:40.000 --> 00:18:42.000 Everything else has not been affected. 00:18:42.000 --> 00:18:43.000 So, you'll see here. 00:18:43.000 --> 00:18:45.000 This one's still 0 for weight. 00:18:45.000 --> 00:18:47.000 This one's still 0 for weight. 00:18:48.000 --> 00:18:49.000 But if you look down here. 00:18:49.000 --> 00:18:51.000 Oh, this one's still 0 for weight. 00:18:51.000 --> 00:18:53.000 But this one here is 7 for weight. 00:18:54.000 --> 00:18:56.000 Whereas, this one here is a 0 for weight. 00:18:57.000 --> 00:18:58.000 How cool is that? 00:18:58.000 --> 00:19:00.000 I was able to manipulate just that one. 00:19:00.000 --> 00:19:05.000 And make sure all traffic for that network goes through who? 00:19:05.000 --> 00:19:08.000 Goes directly to that ISP. 00:19:08.000 --> 00:19:12.000 Where the traffic for all the other ones is still going through R2. 00:19:12.000 --> 00:19:13.000 Except for that one there. 00:19:13.000 --> 00:19:15.000 Because that one is learning directly that way. 00:19:16.000 --> 00:19:17.000 So, anyways. 00:19:17.000 --> 00:19:18.000 Pretty cool. 00:19:18.000 --> 00:19:19.000 When you think about it in the end. 00:19:19.000 --> 00:19:24.000 Having the ability to manipulate that decision making process on your router. 00:19:25.000 --> 00:19:26.000 All right. 00:19:26.000 --> 00:19:28.000 Now, let's talk about local preference. 00:19:29.000 --> 00:19:32.000 So, local preference is another attribute that we have. 00:19:32.000 --> 00:19:33.000 It comes right after weight. 00:19:33.000 --> 00:19:34.000 Remember in our list. 00:19:35.000 --> 00:19:40.000 And local preference is an attribute that is going to be passed to other routers in the autonomous system. 00:19:40.000 --> 00:19:43.000 So, if I manipulate local preference on one router. 00:19:43.000 --> 00:19:46.000 It tells all the other BGP routers in my autonomous system. 00:19:46.000 --> 00:19:48.000 What this new local preference is. 00:19:49.000 --> 00:19:50.000 So, what does that mean? 00:19:50.000 --> 00:19:53.000 It means that you can use local preference. 00:19:54.000 --> 00:19:58.000 To manipulate other routers in your autonomous system. 00:19:59.000 --> 00:20:01.000 To prefer a certain path. 00:20:01.000 --> 00:20:04.000 Remember, local preference default value is 100. 00:20:04.000 --> 00:20:05.000 Higher is better. 00:20:06.000 --> 00:20:11.000 And we can set it for all routes that we share with all the other routers in our autonomous system. 00:20:11.000 --> 00:20:13.000 Or just very specific routes. 00:20:14.000 --> 00:20:15.000 Very specific routes. 00:20:15.000 --> 00:20:16.000 Using a route map. 00:20:18.000 --> 00:20:21.000 So, let's remind ourselves what our environment looks like. 00:20:21.000 --> 00:20:22.000 So, in this case. 00:20:22.000 --> 00:20:23.000 We've got. 00:20:24.000 --> 00:20:25.000 EBGP right here. 00:20:28.000 --> 00:20:29.000 We've got IBGP here. 00:20:29.000 --> 00:20:31.000 We've got IBGP here. 00:20:32.000 --> 00:20:34.000 We've got EBGP here. 00:20:35.000 --> 00:20:36.000 And what's happening down here? 00:20:36.000 --> 00:20:37.000 19. 00:20:37.000 --> 00:20:38.000 Was it 192? 00:20:40.000 --> 00:20:41.000 Is that what we're using? 00:20:45.000 --> 00:20:47.000 Yeah, 192 is the one we're working with. 00:20:47.000 --> 00:20:48.000 192. 00:20:48.000 --> 00:20:49.000 192. 00:20:49.000 --> 00:20:50.000 192. 00:20:50.000 --> 00:20:51.000 192. 00:20:53.000 --> 00:20:55.000 It's tough to remember the numbers you're using when you do it on the fly. 00:20:55.000 --> 00:20:57.000 And you have no notes for any of this stuff. 00:20:59.000 --> 00:21:01.000 And I'm just manipulating it based on what I see. 00:21:02.000 --> 00:21:03.000 So far, so good. 00:21:04.000 --> 00:21:05.000 So. 00:21:05.000 --> 00:21:07.000 Now, let's think about this scenario here. 00:21:07.000 --> 00:21:09.000 If we look at R1. 00:21:10.000 --> 00:21:12.000 We have successfully manipulated weight, right? 00:21:12.000 --> 00:21:14.000 So, that way there it's going this way. 00:21:14.000 --> 00:21:15.000 So, R1 is going this way. 00:21:16.000 --> 00:21:17.000 To get to this network over here. 00:21:19.000 --> 00:21:20.000 That's the way we're going. 00:21:20.000 --> 00:21:21.000 Okay, which way is R2 going? 00:21:21.000 --> 00:21:24.000 Because R2 is in the same autonomous system as R1. 00:21:24.000 --> 00:21:25.000 So, do show IP. 00:21:25.000 --> 00:21:26.000 BGP. 00:21:27.000 --> 00:21:34.000 And we'll see here that to get to that particular network, R2 is choosing the direct path. 00:21:34.000 --> 00:21:37.000 The direct path, 1045.33.2. 00:21:37.000 --> 00:21:39.000 So, 1045.33.2. 00:21:40.000 --> 00:21:41.000 That's the way it's choosing right now. 00:21:44.000 --> 00:21:51.000 So, we could manipulate local preference over here. 00:21:51.000 --> 00:22:02.000 If we change local pref here, we could then influence R2 to potentially actually go this way. 00:22:13.000 --> 00:22:14.000 Interesting, isn't it? 00:22:15.000 --> 00:22:16.000 Absolutely. 00:22:16.000 --> 00:22:24.000 So, for example, over here on R1, if I type in the command that we saw on this last page. 00:22:26.000 --> 00:22:30.000 It says here BGP default local preference and then give it a value. 00:22:30.000 --> 00:22:31.000 So, let's do that. 00:22:32.000 --> 00:22:36.000 BGP default local preference. 00:22:37.000 --> 00:22:38.000 Let's say 150 as an example. 00:22:39.000 --> 00:22:40.000 So, I do this on R1. 00:22:41.000 --> 00:22:44.000 So, this doesn't actually really affect R1. 00:22:45.000 --> 00:22:50.000 Because as you can see in this particular case, it's not changing anything on R1. 00:22:51.000 --> 00:22:55.000 Nothing has changed here on R1 in regards to that. 00:22:59.000 --> 00:23:02.000 But notice, my table has changed, hasn't it? 00:23:03.000 --> 00:23:04.000 It used to be this big. 00:23:06.000 --> 00:23:07.000 Do you see that? 00:23:07.000 --> 00:23:11.000 It used to be this big and now it's only this big. 00:23:14.000 --> 00:23:15.000 Why? 00:23:15.000 --> 00:23:20.000 Because certain things have changed now in this environment. 00:23:21.000 --> 00:23:22.000 That's right. 00:23:22.000 --> 00:23:25.000 So, you notice the ripple effect of change is just by doing that. 00:23:26.000 --> 00:23:28.000 So, let's go over to R2 and see if something happened on R2. 00:23:29.000 --> 00:23:32.000 If we go over to R2, this is the table before on R2. 00:23:33.000 --> 00:23:34.000 Right? 00:23:34.000 --> 00:23:35.000 This is the table now. 00:23:36.000 --> 00:23:39.000 And if we look here closely, please have worked. 00:23:44.000 --> 00:23:47.000 I've got to go do something on R1 to make this a little bit more easier to understand. 00:23:48.000 --> 00:23:54.000 I've got to go to address family IPV4 Unicast. 00:23:54.000 --> 00:23:56.000 I've got to do that command we did before on R2. 00:23:56.000 --> 00:24:03.000 So, neighbor 192.168.255.2 next hop self. 00:24:04.000 --> 00:24:08.000 Because right now, I'm not advertising myself as the next hop. 00:24:09.000 --> 00:24:10.000 I'm advertising. 00:24:12.000 --> 00:24:15.000 I'm preserving the next hop IP address. 00:24:16.000 --> 00:24:19.000 I'm preserving the next hop IP address of the EB2B peer, 00:24:19.000 --> 00:24:22.000 which is going to cause confusion when we look at this output. 00:24:22.000 --> 00:24:25.000 So, let me refresh this and we should see that things are different now. 00:24:27.000 --> 00:24:28.000 There we go. 00:24:28.000 --> 00:24:29.000 Okay. 00:24:29.000 --> 00:24:30.000 So, this is going to make a lot more sense now. 00:24:30.000 --> 00:24:31.000 Okay. 00:24:31.000 --> 00:24:32.000 So, when you look at this output now, 00:24:32.000 --> 00:24:37.000 you're going to see that I now have preferred the path through who? 00:24:38.000 --> 00:24:39.000 Through R1. 00:24:39.000 --> 00:24:40.000 Why? 00:24:40.000 --> 00:24:41.000 Because look at the local preference. 00:24:42.000 --> 00:24:43.000 Look at the local preference. 00:24:44.000 --> 00:24:47.000 So, even though this is a shorter path, and that's the path we were using before. 00:24:47.000 --> 00:24:52.000 If we go back up, before we made these changes, that's the path I was choosing. 00:24:53.000 --> 00:24:54.000 Why? 00:24:54.000 --> 00:24:55.000 It had the lower AS path. 00:24:56.000 --> 00:24:57.000 Lower AS path. 00:24:58.000 --> 00:25:01.000 But now, I'm choosing what? 00:25:01.000 --> 00:25:02.000 R1. 00:25:02.000 --> 00:25:03.000 Why? 00:25:03.000 --> 00:25:04.000 Because we don't even get that far. 00:25:05.000 --> 00:25:07.000 We look at weight. 00:25:07.000 --> 00:25:08.000 Weight is tied. 00:25:08.000 --> 00:25:11.000 And now, we look at local preference, and local preference is 150. 00:25:11.000 --> 00:25:12.000 So, that's what I'm going to use. 00:25:13.000 --> 00:25:14.000 And so, that's the one that ends up in the routing table. 00:25:18.000 --> 00:25:24.000 So, now, all the traffic that leaves R2 to go to this network down here is going to go this way. 00:25:26.000 --> 00:25:28.000 Obviously, that's not the best way to go in our scenario, 00:25:28.000 --> 00:25:31.000 but I'm just trying to show you how manipulating local preference here on R1, 00:25:32.000 --> 00:25:35.000 how that can change other routers' decision-making processes. 00:25:37.000 --> 00:25:40.000 Now, when we look at something like what we just did on R1, 00:25:41.000 --> 00:25:44.000 I said, hey, when you advertise to all your IBGP neighbors, 00:25:45.000 --> 00:25:49.000 tell them the local preference for all routes are going to be 150. 00:25:50.000 --> 00:25:52.000 So, that affected all the traffic, everything. 00:25:52.000 --> 00:25:58.000 But if we wanted to get very specific and just focus on that one network and not affect everything else, 00:25:59.000 --> 00:26:01.000 we could totally do that as well with a route map. 00:26:02.000 --> 00:26:06.000 So, let me erase what we just did on R1 and just show you quickly how we can do that with a route map. 00:26:08.000 --> 00:26:10.000 So, we'll go over to R1. 00:26:11.000 --> 00:26:12.000 Where's the command? 00:26:12.000 --> 00:26:13.000 There it is. 00:26:13.000 --> 00:26:14.000 Let's get rid of that command. 00:26:15.000 --> 00:26:18.000 Let's clear BGP out. 00:26:19.000 --> 00:26:21.000 Let's clear BGP in just to be on the safe side. 00:26:21.000 --> 00:26:22.000 I don't want any stale information. 00:26:22.000 --> 00:26:23.000 Okay. 00:26:23.000 --> 00:26:25.000 Now, we already have a prefix list that's going to match this. 00:26:25.000 --> 00:26:27.000 So, do show IP prefix list. 00:26:28.000 --> 00:26:31.000 So, I am just going to use this exact same prefix list 00:26:31.000 --> 00:26:34.000 because that's the one we want to match in our particular example again. 00:26:36.000 --> 00:26:37.000 So, let's just go ahead and do that. 00:26:38.000 --> 00:26:40.000 We'll just match that exact same prefix list. 00:26:40.000 --> 00:26:43.000 Even though it's called BGP wait, we're just going to use it for the local preference example. 00:26:44.000 --> 00:26:45.000 So, now I'm going to type in a route map. 00:26:45.000 --> 00:26:48.000 We're going to create a new route map, route-map. 00:26:49.000 --> 00:26:53.000 And let's call this one route-map for local preference. 00:26:54.000 --> 00:26:55.000 And we're going to do a permit. 00:26:55.000 --> 00:26:57.000 And we're going to use sequence number 10 in this case. 00:26:58.000 --> 00:26:59.000 And we are going to say match. 00:26:59.000 --> 00:27:00.000 Match what? 00:27:00.000 --> 00:27:03.000 Match the IP address of the prefix list we created called this. 00:27:03.000 --> 00:27:05.000 And the only reason I'm using the same one for this scenario 00:27:05.000 --> 00:27:07.000 is because I want to match that same address. 00:27:08.000 --> 00:27:11.000 And then I'm going to set the local preference. 00:27:12.000 --> 00:27:14.000 I'm going to set the local preference to what? 00:27:14.000 --> 00:27:15.000 Let's go ahead and set it to 177. 00:27:16.000 --> 00:27:17.000 Now, if we exit out of there. 00:27:17.000 --> 00:27:23.000 Again, let's not forget about all the other routes that we still have to catch and match. 00:27:24.000 --> 00:27:26.000 So, match everything else by leaving it blank. 00:27:27.000 --> 00:27:30.000 And because it's a permit, it means that I want to match them in this case. 00:27:31.000 --> 00:27:33.000 And I want to match everything. 00:27:34.000 --> 00:27:37.000 I want to learn about them because I'm using it for BGP. 00:27:37.000 --> 00:27:40.000 And as a result of that, I leave my set as well to blank. 00:27:41.000 --> 00:27:43.000 And it does all the default values of whatever it is. 00:27:43.000 --> 00:27:44.000 So, now that I have that done, 00:27:44.000 --> 00:27:50.000 if we simply go back to the router BGP configuration mode for autonomous system number 65,001, 00:27:51.000 --> 00:27:53.000 then what we're going to be able to do is we're going to type in neighbor. 00:27:54.000 --> 00:27:55.000 Nope. 00:27:55.000 --> 00:27:58.000 We've got to go into address family configuration mode for IPv4 Unicast. 00:27:59.000 --> 00:28:01.000 And let's say neighbor in this case. 00:28:01.000 --> 00:28:04.000 And specifically, we're going to focus on R2. 00:28:05.000 --> 00:28:08.000 So, 192.168.255.who. 00:28:09.000 --> 00:28:11.000 192.168.255.to. 00:28:11.000 --> 00:28:13.000 192.168.255.to. 00:28:14.000 --> 00:28:16.000 Apply a route map of what? 00:28:16.000 --> 00:28:21.000 Apply the route map called route map local preference that we created. 00:28:21.000 --> 00:28:23.000 And in this case, outbound. 00:28:23.000 --> 00:28:25.000 So, what I am teaching, 00:28:25.000 --> 00:28:33.000 what I am teaching router number to 192.168.255.to about my BGP routes that I know about, 00:28:34.000 --> 00:28:39.000 I want to make sure that this route map is applied when I teach them. 00:28:39.000 --> 00:28:41.000 So, what is it going to be? 00:28:41.000 --> 00:28:48.000 I am going to set the local preference to 177 for any network that matches this prefix list, 00:28:49.000 --> 00:28:51.000 which happens to be this one here. 00:28:51.000 --> 00:28:55.000 And then all the other ones, I'm not going to do anything to them. 00:28:55.000 --> 00:28:58.000 I'm just going to leave them blank, but I'm still going to teach them. 00:28:58.000 --> 00:28:59.000 Or, sorry, not leave them blank. 00:28:59.000 --> 00:29:04.000 I'm going to leave them with their default values, and I'm going to send those to R2. 00:29:05.000 --> 00:29:07.000 So, let's clear the BGP process here for ourselves. 00:29:10.000 --> 00:29:14.000 Basically, tickle your neighbor, update them, essentially what I'm doing. 00:29:14.000 --> 00:29:16.000 So, now we go over to R2. 00:29:16.000 --> 00:29:19.000 We should see here over on R2 that this is what we had before. 00:29:19.000 --> 00:29:23.000 These should all be back to 100 except for this one right here. 00:29:23.000 --> 00:29:27.000 This is the only one that should now be 177. 00:29:27.000 --> 00:29:28.000 And there you go. 00:29:31.000 --> 00:29:35.000 So, now I've been able to influence that one specifically on R2, 00:29:36.000 --> 00:29:37.000 but only R2. 00:29:37.000 --> 00:29:40.000 I haven't influenced it on anybody else, just R2, 00:29:42.000 --> 00:29:46.000 forcing R2 to come through me in order to get to that particular network. 00:29:47.000 --> 00:29:50.000 So, again, when you're using this command here, 00:29:50.000 --> 00:29:56.000 it affects all your IBGP neighbors and all the routes that you share with them. 00:29:56.000 --> 00:30:00.000 Whereas when you use a route map, you can pick and choose what BGP neighbors you affect, 00:30:01.000 --> 00:30:03.000 IBGP neighbors you share with them. 00:30:04.000 --> 00:30:05.000 IBGP neighbors you affect, 00:30:05.000 --> 00:30:08.000 and you can pick and choose what routes you want to affect as well. 00:30:11.000 --> 00:30:12.000 All right. 00:30:12.000 --> 00:30:15.000 So, those two, wait and local preference, as you can see, 00:30:15.000 --> 00:30:22.000 are really valuable manipulators for manipulating traffic leaving your environment. 00:30:23.000 --> 00:30:24.000 Let me repeat that. 00:30:24.000 --> 00:30:27.000 Pay attention right now to the directionality. 00:30:28.000 --> 00:30:31.000 Wait and local preference allows me to manipulate what? 00:30:31.000 --> 00:30:35.000 Traffic that is leaving my environment. 00:30:36.000 --> 00:30:41.000 So, when we used wait, I was able to manipulate that router specifically 00:30:41.000 --> 00:30:44.000 and indicate which way I wanted it to go. 00:30:45.000 --> 00:30:47.000 Whereas with local preference, 00:30:47.000 --> 00:30:51.000 I can now manipulate other routers' decision-making processes 00:30:51.000 --> 00:30:53.000 that are running BGP in that autonomous system. 00:30:54.000 --> 00:30:58.000 So, basically, by setting local preference on R1, 00:30:58.000 --> 00:31:00.000 when it tells all the other routers, 00:31:00.000 --> 00:31:03.000 hey, locally prefer me. 00:31:03.000 --> 00:31:04.000 Ah, you get the name now, 00:31:04.000 --> 00:31:06.000 if you're having trouble making a connection to that name. 00:31:06.000 --> 00:31:12.000 Locally prefer me as the way to get to those networks. 00:31:12.000 --> 00:31:16.000 So, now the other routers running BGP will prefer that router 00:31:16.000 --> 00:31:18.000 to get to wherever they need to go. 00:31:19.000 --> 00:31:22.000 But what about manipulating traffic coming back to you? 00:31:23.000 --> 00:31:27.000 What about manipulating traffic that is coming back to you? 00:31:28.000 --> 00:31:29.000 You ever thought about that? 00:31:36.000 --> 00:31:39.000 Because right now, look at this environment. 00:31:39.000 --> 00:31:41.000 We want to make sure all traffic goes this way. 00:31:41.000 --> 00:31:43.000 All traffic is going this way. 00:31:44.000 --> 00:31:46.000 See the flow from my environment, 00:31:46.000 --> 00:31:48.000 it's got to go this way and this way. 00:31:48.000 --> 00:31:50.000 Never go this way right now. 00:31:51.000 --> 00:31:56.000 Well, let's see what path they're taking to get to me, 00:31:57.000 --> 00:31:58.000 my network. 00:31:59.000 --> 00:32:02.000 So, what network do we have right now that we're advertising? 00:32:02.000 --> 00:32:05.000 I believe it's 10.0.0.0 size 24, right? 00:32:05.000 --> 00:32:07.000 I think we advertised that one earlier. 00:32:07.000 --> 00:32:12.000 So, if we go right now to branch, 00:32:12.000 --> 00:32:14.000 we should see that one in its table. 00:32:14.000 --> 00:32:15.000 Yep, there it is. 00:32:15.000 --> 00:32:16.000 Okay. 00:32:16.000 --> 00:32:18.000 So, how is it getting back to us? 00:32:18.000 --> 00:32:21.000 Well, it is choosing to go which way? 00:32:21.000 --> 00:32:24.000 It is choosing to go this way, it looks like. 00:32:26.000 --> 00:32:31.000 So, it has chosen 10.45.33.1. 00:32:32.000 --> 00:32:33.000 And why? 00:32:33.000 --> 00:32:36.000 Well, it's because it's the lowest AS path. 00:32:36.000 --> 00:32:38.000 Weights tied, local preference tied, 00:32:38.000 --> 00:32:40.000 it wasn't a locally originated. 00:32:40.000 --> 00:32:44.000 So, we are dealing with the lowest AS path. 00:32:44.000 --> 00:32:48.000 Well, what if this was our primary ISP 00:32:49.000 --> 00:32:50.000 and this was our backup? 00:32:51.000 --> 00:32:52.000 What does that mean? 00:32:52.000 --> 00:32:55.000 One, it means that traffic going to the internet 00:32:55.000 --> 00:32:58.000 is following the primary path like we want it to, 00:32:58.000 --> 00:33:00.000 but traffic coming back to us 00:33:00.000 --> 00:33:01.000 is going through our backup path. 00:33:01.000 --> 00:33:04.000 Let's say it's costing us a lot of money. 00:33:04.000 --> 00:33:06.000 Well, that's no good, right? 00:33:06.000 --> 00:33:08.000 So, if traffic's coming back this way 00:33:08.000 --> 00:33:09.000 across our backup path, 00:33:09.000 --> 00:33:12.000 it's going to cost us a lot of money. 00:33:12.000 --> 00:33:14.000 And if traffic's coming back this way 00:33:14.000 --> 00:33:15.000 across our backup path, 00:33:15.000 --> 00:33:17.000 that's costing us too much money. 00:33:19.000 --> 00:33:22.000 But also, look at the traffic flow. 00:33:22.000 --> 00:33:24.000 Traffic leaves our environment here, 00:33:24.000 --> 00:33:26.000 comes back here, leaves our environment here. 00:33:26.000 --> 00:33:28.000 That's what we call what? 00:33:28.000 --> 00:33:29.000 Asymmetric routing. 00:33:29.000 --> 00:33:31.000 And because of that asymmetric routing, 00:33:31.000 --> 00:33:34.000 it's quite possible that the traffic coming back to us 00:33:34.000 --> 00:33:36.000 could be bypassing security features. 00:33:36.000 --> 00:33:40.000 It definitely would have a NAT problem, wouldn't we? 00:33:40.000 --> 00:33:41.000 In this type of scenario. 00:33:41.000 --> 00:33:43.000 There's a lot of other things that would be a problem. 00:33:43.000 --> 00:33:46.000 So, how can I influence the traffic 00:33:46.000 --> 00:33:51.000 to actually come back this way instead? 00:33:52.000 --> 00:33:57.000 Well, Casey typed in autonomous system path prepending. 00:33:58.000 --> 00:34:01.000 Autonomous system path prepending. 00:34:01.000 --> 00:34:03.000 What does that mean? 00:34:03.000 --> 00:34:08.000 Let's make this path look horrible. 00:34:08.000 --> 00:34:10.000 That's what we're going to do. 00:34:10.000 --> 00:34:13.000 We are going to lie to the internet 00:34:13.000 --> 00:34:16.000 by doing AS path prepending. 00:34:16.000 --> 00:34:18.000 With AS path prepending, 00:34:18.000 --> 00:34:25.000 what we do is we add additional autonomous system hops. 00:34:25.000 --> 00:34:27.000 Now, what autonomous system number do we use? 00:34:27.000 --> 00:34:28.000 Our own. 00:34:28.000 --> 00:34:29.000 Don't use anybody else's. 00:34:29.000 --> 00:34:31.000 Use your own autonomous system number. 00:34:31.000 --> 00:34:33.000 And so, if normally, 00:34:33.000 --> 00:34:36.000 as we can see in this particular scenario, 00:34:36.000 --> 00:34:40.000 what they have is they've learned it's 65,001. 00:34:40.000 --> 00:34:44.000 Well, what if we made it 65,001, 65,001, 65,001, 65,001, 00:34:44.000 --> 00:34:47.000 65,001, 65,001, 65,001, 65,001? 00:34:47.000 --> 00:34:52.000 Well, then that's worse than 65,000 and 65,001. 00:34:52.000 --> 00:34:56.000 So, what path do you think Branch is now going to use? 00:34:56.000 --> 00:34:58.000 Branch is now going to use the one with the lower AS path. 00:34:58.000 --> 00:35:00.000 That's all I'm doing here. 00:35:00.000 --> 00:35:03.000 I'm just basically tricking it to use that other path. 00:35:03.000 --> 00:35:05.000 So, that's what we're going to do here. 00:35:05.000 --> 00:35:06.000 We're going to go ahead on R2. 00:35:06.000 --> 00:35:10.000 We're going to tell this neighbor that to get here, 00:35:10.000 --> 00:35:13.000 it's 65,001, 65,001, 65,001, 65,001. 00:35:13.000 --> 00:35:17.000 I can put as many as I want, but we're going to do four. 00:35:17.000 --> 00:35:20.000 So, over on R2, we need a route map to do this. 00:35:20.000 --> 00:35:21.000 So, let's back out of here. 00:35:21.000 --> 00:35:22.000 Let's back out of here. 00:35:22.000 --> 00:35:26.000 And we're going to type in route map. 00:35:26.000 --> 00:35:30.000 We're going to call it AS path prepend, pre, just so we know. 00:35:30.000 --> 00:35:32.000 It's AS path prepending route map that we're creating here. 00:35:33.000 --> 00:35:35.000 Permit sequence number 10. 00:35:35.000 --> 00:35:37.000 And we want to match everything. 00:35:37.000 --> 00:35:39.000 Everything we teach, that router right now. 00:35:39.000 --> 00:35:42.000 Now, in your case, it might not be everything. 00:35:42.000 --> 00:35:45.000 It might be very specific networks. 00:35:45.000 --> 00:35:46.000 And if it's very specific networks, what do you do? 00:35:46.000 --> 00:35:48.000 Create a prefix list. 00:35:48.000 --> 00:35:50.000 And then with that prefix list, you match it. 00:35:50.000 --> 00:35:53.000 Then you match the prefix list here, and then you set it. 00:35:53.000 --> 00:35:54.000 But in my case, I'm just going to do all. 00:35:54.000 --> 00:35:59.000 Everything I teach you, I'm going to prepend like crazy. 00:35:59.000 --> 00:36:02.000 But, again, you can get very specific. 00:36:02.000 --> 00:36:06.000 And if you want certain routes this way to have a prepend, 00:36:06.000 --> 00:36:08.000 and other routes up here to have a prepend, 00:36:08.000 --> 00:36:13.000 then you can control different traffic on different paths. 00:36:13.000 --> 00:36:14.000 So, AS path prepending match. 00:36:14.000 --> 00:36:16.000 I'll leave blank, meaning match everything. 00:36:16.000 --> 00:36:23.000 And now I'm just going to say set AS path prepend to, we said, 00:36:24.000 --> 00:36:30.000 65,001, 65,001, 65,001. 00:36:30.000 --> 00:36:34.000 And I also said, I think, 65,001. 00:36:34.000 --> 00:36:35.000 All right. 00:36:35.000 --> 00:36:37.000 Now, if you use other wrong Autonomous System numbers, 00:36:37.000 --> 00:36:38.000 you could cause problems out on the Internet. 00:36:38.000 --> 00:36:41.000 So that's why you should only use your own. 00:36:41.000 --> 00:36:43.000 All right. 00:36:43.000 --> 00:36:44.000 Now, since we're matching everything here, 00:36:44.000 --> 00:36:46.000 I don't need a sequence number 20, 00:36:46.000 --> 00:36:47.000 because I'm matching everything here. 00:36:47.000 --> 00:36:50.000 So it catches everything. 00:36:50.000 --> 00:36:54.000 So now we go to router, BGP, 65,001. 00:36:54.000 --> 00:36:59.000 And we say address family IPV for Unicast. 00:36:59.000 --> 00:37:00.000 And then we type in neighbor. 00:37:00.000 --> 00:37:01.000 And who's our neighbor? 00:37:01.000 --> 00:37:06.000 10.45.33.2, that's our neighbor. 00:37:06.000 --> 00:37:10.000 And we're going to now say that we want to do a route map. 00:37:10.000 --> 00:37:12.000 We're going to apply a route map to them. 00:37:12.000 --> 00:37:17.000 And the route map we're applying is the AS path prepending a route map. 00:37:17.000 --> 00:37:19.000 And then we're going to say in the outbound direction. 00:37:19.000 --> 00:37:23.000 So when I teach, when I teach that neighbor about what I want to teach them, 00:37:23.000 --> 00:37:30.000 I am going to teach them that everything has this added to it. 00:37:30.000 --> 00:37:38.000 So let's type in do show, not do show, do clear IP BGP star out and in, 00:37:38.000 --> 00:37:41.000 just to be on the safe side, make sure we totally refresh everything here. 00:37:41.000 --> 00:37:45.000 So as you can see, BGP doesn't automatically refresh itself. 00:37:45.000 --> 00:37:48.000 As soon as you make a change, you have to force those refreshes. 00:37:48.000 --> 00:37:51.000 So now we're going to go ahead and type what? 00:37:51.000 --> 00:37:52.000 Oh, we got to go over to branch. 00:37:52.000 --> 00:37:53.000 That's where we got to go. 00:37:53.000 --> 00:37:55.000 And so if I did everything right, 00:37:55.000 --> 00:37:58.000 you should see that everything learned from this neighbor, 00:37:58.000 --> 00:38:00.000 everything learned from this neighbor, 00:38:00.000 --> 00:38:09.000 is now going to have a very excessive, a very excessive what? 00:38:09.000 --> 00:38:14.000 AS path attribute. 00:38:14.000 --> 00:38:19.000 And there you go. 00:38:19.000 --> 00:38:20.000 So what does that mean? 00:38:20.000 --> 00:38:21.000 It means we should have a change. 00:38:21.000 --> 00:38:25.000 So what network we were focusing on specifically, it was this one here. 00:38:25.000 --> 00:38:28.000 So originally we were using 10, 45, 33, one, 00:38:28.000 --> 00:38:30.000 but now we should be using this one here. 00:38:30.000 --> 00:38:32.000 So let's verify that. 00:38:32.000 --> 00:38:33.000 And the answer is yes, we are. 00:38:33.000 --> 00:38:34.000 Look at that. 00:38:34.000 --> 00:38:38.000 We're using this one because it's two versus that. 00:38:38.000 --> 00:38:42.000 So now traffic is flowing this way as we want it to. 00:38:42.000 --> 00:38:47.000 Now up here, up here, it might not be flowing that way. 00:38:47.000 --> 00:38:50.000 It might actually be flowing this way, 00:38:50.000 --> 00:38:54.000 which means that we still have to think about other connections, right? 00:38:54.000 --> 00:38:56.000 Because this is an EBGP connection as well here. 00:38:56.000 --> 00:39:03.000 So might I have to lie to this neighbor as well to make sure they also go that way? 00:39:03.000 --> 00:39:04.000 Absolutely. 00:39:04.000 --> 00:39:06.000 Absolutely. 00:39:06.000 --> 00:39:11.000 So I'm pretty sure if I go to ISPA, it's probably pointing down, right? 00:39:12.000 --> 00:39:14.000 Right now still to R2. 00:39:14.000 --> 00:39:16.000 So it's just something to keep in mind for the real world, 00:39:16.000 --> 00:39:20.000 that you have to keep an eye and pay attention to all the possible options 00:39:20.000 --> 00:39:21.000 while you're doing this. 00:39:21.000 --> 00:39:22.000 So let's see here. 00:39:22.000 --> 00:39:25.000 Yep. 00:39:25.000 --> 00:39:26.000 Nope. 00:39:26.000 --> 00:39:28.000 Actually, it's going to R1 right now. 00:39:28.000 --> 00:39:30.000 That is R1 as the neighbor. 00:39:30.000 --> 00:39:31.000 That is R1. 00:39:31.000 --> 00:39:33.000 But look at this one here. 00:39:33.000 --> 00:39:34.000 Okay, that's R2. 00:39:34.000 --> 00:39:38.000 So it is why was that one chosen? 00:39:38.000 --> 00:39:40.000 Okay, so this one was chosen because the metric. 00:39:40.000 --> 00:39:46.000 You see the metric here is zero, but the metric here is two. 00:39:46.000 --> 00:39:49.000 And the reason why is because we did redistribution, 00:39:49.000 --> 00:39:53.000 if I recall correctly, for this one. 00:39:53.000 --> 00:39:55.000 No, it was network command. 00:39:55.000 --> 00:39:57.000 But the metric was preserved. 00:39:57.000 --> 00:40:00.000 Okay, but over here, the thing is, is that that is an IBGP. 00:40:00.000 --> 00:40:01.000 It was learned via IBGP. 00:40:01.000 --> 00:40:02.000 There's a lot of things. 00:40:02.000 --> 00:40:03.000 The reason why the metric here is zero. 00:40:03.000 --> 00:40:07.000 So actually, it's the metric that is making the choice here. 00:40:07.000 --> 00:40:08.000 So we would have to be careful. 00:40:08.000 --> 00:40:10.000 We would have to think, okay, wait a second. 00:40:10.000 --> 00:40:16.000 If metrics being the choice, then I might want to manipulate that AS path. 00:40:16.000 --> 00:40:20.000 So that way there down the road, that metric, if it ever changes, 00:40:20.000 --> 00:40:23.000 does not ultimately change and cause traffic to come this way. 00:40:23.000 --> 00:40:25.000 So, again, advanced BGP, 00:40:25.000 --> 00:40:27.000 you've got to be thinking of every single possible scenario 00:40:27.000 --> 00:40:28.000 to get the result that you want. 00:40:28.000 --> 00:40:30.000 But in this case, what was our goal? 00:40:30.000 --> 00:40:35.000 Our goal was primarily force this router to go that way, which we have done. 00:40:35.000 --> 00:40:37.000 So we've accomplished our objective in this scenario 00:40:37.000 --> 00:40:40.000 with AS path prepending. 00:40:40.000 --> 00:40:44.000 All right, and lastly, lastly, what do we have next to cover? 00:40:44.000 --> 00:40:47.000 And that is going to be a discussion on MED. 00:40:47.000 --> 00:40:55.000 All right, so MED is called the metric. 00:40:55.000 --> 00:41:02.000 And MED, as we saw, is something that can be used for many different purposes. 00:41:03.000 --> 00:41:08.000 So, for example, if we are using MPLS, 00:41:08.000 --> 00:41:14.000 then when I redistribute from OSPF into BGP or EIGRP into BGP for MPLS, 00:41:14.000 --> 00:41:18.000 then the metric of OSPF or EIGRP can be placed in the MED field. 00:41:18.000 --> 00:41:22.000 That's why it's called metric in the actual output on a Cisco router. 00:41:22.000 --> 00:41:25.000 But we can still manipulate metric, 00:41:25.000 --> 00:41:29.000 because metric is something that is passed to another autonomous system. 00:41:29.000 --> 00:41:32.000 It's very beneficial when you have dual-homed connections, 00:41:32.000 --> 00:41:35.000 dual-homed connections, 00:41:35.000 --> 00:41:41.000 because I can influence the MED for one path versus the other path 00:41:41.000 --> 00:41:45.000 going to the same autonomous system. 00:41:45.000 --> 00:41:48.000 So, for example, in a scenario where you have your router here, 00:41:48.000 --> 00:41:51.000 dual-connected up to a router here, 00:41:51.000 --> 00:41:54.000 and this is a big, giant autonomous system with lots and lots and lots and lots 00:41:54.000 --> 00:41:57.000 and lots of routers, and let's say there's another autonomous system here, 00:41:57.000 --> 00:41:59.000 another one here, another one here, all right, 00:41:59.000 --> 00:42:01.000 and then you're connected back up here. 00:42:01.000 --> 00:42:04.000 If I can tell this autonomous system here, 00:42:04.000 --> 00:42:07.000 I want you to prefer this way. 00:42:07.000 --> 00:42:12.000 I want you, you, you to prefer this path right here, 00:42:12.000 --> 00:42:16.000 then I can influence this autonomous system to make sure that they're coming 00:42:16.000 --> 00:42:18.000 along this path. 00:42:18.000 --> 00:42:20.000 I'm not influencing anybody else. 00:42:20.000 --> 00:42:22.000 I'm not affecting anybody else with MED. 00:42:22.000 --> 00:42:25.000 I'm just influencing the directly connected autonomous system in that 00:42:25.000 --> 00:42:27.000 particular case. 00:42:27.000 --> 00:42:32.000 So, when we look at our topology, we have dual connections here. 00:42:32.000 --> 00:42:35.000 What if this is a primary link and this is a backup link, 00:42:35.000 --> 00:42:37.000 and it's this link that's being used? 00:42:37.000 --> 00:42:39.000 Well, that's no good. 00:42:39.000 --> 00:42:42.000 I don't want that to be used by the upstream autonomous system. 00:42:42.000 --> 00:42:44.000 I want this one to be used. 00:42:44.000 --> 00:42:46.000 So, MED is what, higher or lower? 00:42:46.000 --> 00:42:48.000 What is better? 00:42:48.000 --> 00:42:53.000 Lower MED is better. 00:42:53.000 --> 00:42:55.000 So, lower MED is better. 00:42:55.000 --> 00:42:57.000 Lower MED is more preferred. 00:42:57.000 --> 00:43:04.000 So, if I set the MED, the metric, and then I tell a router, hey, 00:43:04.000 --> 00:43:07.000 this is the MED now for this path, 00:43:07.000 --> 00:43:14.000 then that means that I can get that neighboring autonomous system to choose 00:43:14.000 --> 00:43:17.000 one path over the other directly back to me. 00:43:17.000 --> 00:43:20.000 So, great for like those dual home scenarios, for example, with an ISP. 00:43:21.000 --> 00:43:23.000 So, if we come back to this scenario here, 00:43:23.000 --> 00:43:29.000 let's just take a peek at R2 right now, not R2, ISP, 00:43:29.000 --> 00:43:33.000 and see if we can do something with this. 00:43:33.000 --> 00:43:38.000 Let's just see if we can do something with this and make it work. 00:43:38.000 --> 00:43:43.000 So, is the ISP choosing anything? 00:43:43.000 --> 00:43:45.000 Yeah, sure, this one right here. 00:43:46.000 --> 00:43:52.000 So, right now, let's focus on 10. 00:43:58.000 --> 00:44:00.000 Let's make sure that's R2. 00:44:01.000 --> 00:44:03.000 91. 00:44:03.000 --> 00:44:05.000 Perfect. 00:44:05.000 --> 00:44:07.000 All right. 00:44:07.000 --> 00:44:12.000 So, you can see here, it's a little bit more complicated than I thought. 00:44:12.000 --> 00:44:15.000 So, let's see if we can do something with this. 00:44:15.000 --> 00:44:18.000 So, let's see if we can do something with this. 00:44:18.000 --> 00:44:20.000 So, let's see if we can do something with this. 00:44:20.000 --> 00:44:23.000 So, let's see if we can do something with this. 00:44:24.000 --> 00:44:25.000 91. 00:44:25.000 --> 00:44:26.000 Perfect. 00:44:26.000 --> 00:44:28.000 All right. 00:44:28.000 --> 00:44:32.000 So, you can see we're choosing this path right here. 00:44:35.000 --> 00:44:38.000 But we also have this path right here. 00:44:42.000 --> 00:44:47.000 So, what we're going to do is we're going to look here at how that decision was made. 00:44:47.000 --> 00:44:49.000 So, weight is tied. 00:44:49.000 --> 00:44:52.000 Local preference is tied. 00:44:52.000 --> 00:44:53.000 Origin code learned. 00:44:53.000 --> 00:44:55.000 All of them were learned, so tied. 00:44:55.000 --> 00:44:58.000 AS path tied. 00:44:58.000 --> 00:45:05.000 And we keep going down the list because med right now is tied at zero for all of them. 00:45:06.000 --> 00:45:13.000 More than likely, it was based on the higher router ID or the higher neighboring IP address. 00:45:13.000 --> 00:45:14.000 That would be more than likely. 00:45:14.000 --> 00:45:15.000 So, we went all the way to the bottom. 00:45:15.000 --> 00:45:16.000 Okay. 00:45:16.000 --> 00:45:18.000 All the way to the bottom of the list here. 00:45:18.000 --> 00:45:23.000 So, what we're going to do is we're going to make med because the decision was made after med, 00:45:23.000 --> 00:45:26.000 then I can manipulate med and accomplish my objective here. 00:45:26.000 --> 00:45:29.000 So, what we're going to do is remember, we're going to go to R2. 00:45:29.000 --> 00:45:34.000 That's where we're going to do the changes because med allows you to influence the neighboring autonomous system, 00:45:34.000 --> 00:45:38.000 not your own, your neighboring autonomous system to control how traffic comes back to you. 00:45:38.000 --> 00:45:45.000 So, we're going to go to R2, and we're going to force the ISP to use this link instead. 00:45:46.000 --> 00:45:48.000 So, we want this one to be the primary one. 00:45:48.000 --> 00:45:49.000 Let me start. 00:45:51.000 --> 00:45:58.000 So, what we're going to do is we're going to make this one look bad, and therefore, this one look good. 00:45:59.000 --> 00:46:04.000 Now, the problem is I might do that, and it might actually choose this one instead, okay? 00:46:04.000 --> 00:46:12.000 That's probably what's going to happen to us, but I just want to show, and then, which means we have to go manipulate R1. 00:46:12.000 --> 00:46:14.000 I'm thinking that that might be the result. 00:46:14.000 --> 00:46:16.000 Just based on what? 00:46:16.000 --> 00:46:18.000 The list, but it shouldn't be. 00:46:18.000 --> 00:46:21.000 No, because med would be tied between this one and this one. 00:46:21.000 --> 00:46:25.000 So, my example might not work unless we influence R1 as well. 00:46:25.000 --> 00:46:26.000 So, let's do that. 00:46:26.000 --> 00:46:27.000 Let's make it work. 00:46:27.000 --> 00:46:29.000 Let's show you how we can make it work in total. 00:46:29.000 --> 00:46:31.000 We might have to go to two routers for this one. 00:46:31.000 --> 00:46:33.000 So, let's create a route map. 00:46:35.000 --> 00:46:43.000 So, route map, and in this case, let's call it med, and it's going to be permit. 00:46:44.000 --> 00:46:48.000 And sequence number 10, and now we're going to match everything. 00:46:48.000 --> 00:46:54.000 So, match everything, and we're going to set the metric to, we got to set it higher. 00:46:54.000 --> 00:46:56.000 So, zero is the default. 00:46:56.000 --> 00:46:59.000 So, let's set it to something like five, all right? 00:46:59.000 --> 00:47:02.000 And since we matched everything, I don't need another sequence. 00:47:02.000 --> 00:47:09.000 Now, let's go ahead and go to router BGP configuration mode for what autonomous system? 00:47:10.000 --> 00:47:19.000 For our local autonomous system is 65,001, and now we're going to type in address family IPV4 Unicast, 00:47:19.000 --> 00:47:23.000 and we're going to type in our neighbor, and our neighbor in this case is going to be who? 00:47:23.000 --> 00:47:25.000 Okay, we want to make this one look bad. 00:47:25.000 --> 00:47:29.000 So, we want to up the med on this one. 00:47:29.000 --> 00:47:34.000 So, it's the neighbor 2030113, in this case, 89. 00:47:34.000 --> 00:47:46.000 So, neighbor 2030113.89, and we are now going to type in, apply the route map when you talk to that particular neighbor, 00:47:46.000 --> 00:47:51.000 and the route map you're going to apply is the med route map in the outbound direction. 00:47:51.000 --> 00:47:57.000 Why? Because when I tell you about it, when I tell you about it, I want you to up your med. 00:47:58.000 --> 00:48:11.000 Good. So, let's clear IPBGP, and let's just go see if that applied to ISPA right now, 00:48:11.000 --> 00:48:15.000 and we'll see how it does not affect this autonomous system at all. 00:48:15.000 --> 00:48:17.000 So, we'll go check their output as well. 00:48:17.000 --> 00:48:20.000 So, you should see here that the med is now five. 00:48:20.000 --> 00:48:21.000 The med is now five. 00:48:21.000 --> 00:48:22.000 You see that? 00:48:23.000 --> 00:48:31.000 But if we go to branch, you'll see that this has no effect on branch because med is not going to be shared with other autonomous systems. 00:48:31.000 --> 00:48:35.000 So, if I tell you to set your med to five, then you're going to set it, 00:48:35.000 --> 00:48:39.000 but you're not going to tell other routers to set their med to five or other networks. 00:48:39.000 --> 00:48:43.000 Now, would it apply to all the routers in your autonomous system? Yes. 00:48:43.000 --> 00:48:50.000 So, when I send that to the ISP as an example, all their routers will be affected, not just the neighboring router, all their routers. 00:48:51.000 --> 00:48:54.000 So, we'll see here now, and I was right. 00:48:54.000 --> 00:48:58.000 You see how this one was chosen now. 00:48:58.000 --> 00:49:01.000 So, I have not been able to accomplish my objective just with this. 00:49:01.000 --> 00:49:07.000 So, let's go over to R1 and make R1 do the exact same thing just as an example. 00:49:07.000 --> 00:49:09.000 So, we'll go to R1 now. 00:49:09.000 --> 00:49:14.000 So, basically, we'll tell that one to set the med to five as well, let's say, as an example. 00:49:14.000 --> 00:49:24.000 So, router or route map, I should say, we'll call this one med as well, permit, sequence number 10. 00:49:24.000 --> 00:49:28.000 And then we're going to say set med to, let's say, six, just so we can tell the difference between the two. 00:49:28.000 --> 00:49:32.000 And it's actually met, Rick, on our router. 00:49:32.000 --> 00:49:36.000 And now we're going to go to router BGP 65,001. 00:49:36.000 --> 00:49:40.000 And when you're talking to your neighbor, who's our neighbor in this case? 00:49:40.000 --> 00:49:42.000 What is their address? 00:49:42.000 --> 00:49:44.000 Their address is going to be this right here. 00:49:44.000 --> 00:49:46.000 Boom, boom, put that in. 00:49:46.000 --> 00:49:48.000 And then we're going to say we want to apply the route map. 00:49:48.000 --> 00:49:50.000 No, I've got to go to what? 00:49:50.000 --> 00:49:56.000 I have to go to address family IPV4 Unicast. 00:49:56.000 --> 00:50:00.000 Then I can apply this command with the route map to it. 00:50:00.000 --> 00:50:04.000 And then it's going to be route map. 00:50:04.000 --> 00:50:05.000 What did we call it? 00:50:05.000 --> 00:50:06.000 We called it med. 00:50:06.000 --> 00:50:10.000 And then we want to apply it outbound. 00:50:10.000 --> 00:50:12.000 Outbound, outbound. 00:50:12.000 --> 00:50:24.000 So when we teach that neighbor, when we teach that neighbor, we want their med to be six. 00:50:24.000 --> 00:50:26.000 So let's go to ISPA now. 00:50:26.000 --> 00:50:36.000 And we should see that this one here, or sorry, this one here is now going to be listed as five as well, because we just told R1 to do that. 00:50:36.000 --> 00:50:39.000 So let's see if that took, or six, not five, but six. 00:50:39.000 --> 00:50:40.000 So there we go. 00:50:40.000 --> 00:50:47.000 So now you'll see that that one's six, that one's five, and you'll see that this one is still zero. 00:50:47.000 --> 00:50:50.000 And notice that's the one that's now installed in the routing table. 00:50:50.000 --> 00:51:00.000 So now by manipulating even this one here, we have been able to make sure that this is the primary path coming back into that autonomous system. 00:51:00.000 --> 00:51:02.000 That's what we've done. 00:51:02.000 --> 00:51:13.000 So, yeah, as you can see, all of these attributes can be manipulated to ultimately determine what is the way that AWS, why did I say AWS, 00:51:13.000 --> 00:51:20.000 the way that the neighboring autonomous system is going to use in order to get back to that particular environment. 00:51:20.000 --> 00:51:24.000 So might you have to manipulate these on the exam? 00:51:24.000 --> 00:51:25.000 Possibly. 00:51:25.000 --> 00:51:27.000 Might you have to manipulate them around maps? 00:51:27.000 --> 00:51:28.000 Possibly. 00:51:28.000 --> 00:51:43.000 Might you just have to know, for example, that if you have a router with multiple paths that it can take, how do you force this router to take this specific path? 00:51:43.000 --> 00:51:52.000 Folks, how would you force this router to take this specific path if, let's say, it was going this way instead? 00:51:52.000 --> 00:51:54.000 How would you make it use this path instead? 00:51:54.000 --> 00:51:55.000 Chat in. 00:51:55.000 --> 00:51:59.000 Which of those four attributes would you manipulate? 00:51:59.000 --> 00:52:00.000 Okay. 00:52:00.000 --> 00:52:02.000 So it's outbound manipulation. 00:52:02.000 --> 00:52:06.000 So you've got two options, wait and local preference. 00:52:06.000 --> 00:52:10.000 So if you're trying to influence that exact router, it is wait. 00:52:10.000 --> 00:52:11.000 Casey, you got it. 00:52:11.000 --> 00:52:12.000 Well done. 00:52:12.000 --> 00:52:13.000 Wait would be the answer. 00:52:13.000 --> 00:52:14.000 Okay. 00:52:14.000 --> 00:52:22.000 Now, what if, for example, you were on this router here, but the scenario was you want this router to go this way? 00:52:22.000 --> 00:52:31.000 Or all your routers in your environment to all go this way to get to that network? 00:52:31.000 --> 00:52:34.000 How could you do that? 00:52:34.000 --> 00:52:37.000 Well, could I go to all the routers and use wait? 00:52:37.000 --> 00:52:39.000 Yes, I technically could, right? 00:52:39.000 --> 00:52:40.000 I could. 00:52:40.000 --> 00:52:43.000 But what if I told you I wanted to do it on R2? 00:52:43.000 --> 00:52:46.000 Then what do you use? 00:52:46.000 --> 00:52:48.000 Again, outbound traffic flow. 00:52:49.000 --> 00:52:52.000 So if it's outbound, wait or local preference. 00:52:52.000 --> 00:53:03.000 Well, which one of those, wait or local preference, allows you to influence other routers in your autonomous system? 00:53:03.000 --> 00:53:04.000 Right, local preference. 00:53:04.000 --> 00:53:09.000 Remember, locally prefer me as your exit point out of the environment. 00:53:09.000 --> 00:53:14.000 Think of it that way. 00:53:15.000 --> 00:53:28.000 If you were trying to manipulate inbound traffic flow from the entire internet, what option would be a good option to choose? 00:53:28.000 --> 00:53:30.000 Casey, you typed it in earlier. 00:53:36.000 --> 00:53:40.000 Yep, AS path prepending. 00:53:40.000 --> 00:53:41.000 Exactly. 00:53:41.000 --> 00:53:43.000 AS path prepending. 00:53:44.000 --> 00:53:59.000 And then if you wanted to influence a directly connected autonomous system that's connected to you multiple times, like we have here, dual connections, you could use what? 00:53:59.000 --> 00:54:05.000 MED or the metric to influence what path's being utilized to get back to you. 00:54:05.000 --> 00:54:07.000 So MED and local preference. 00:54:07.000 --> 00:54:12.000 No, MED and AS path prepending used to influence traffic coming to you. 00:54:12.000 --> 00:54:16.000 Wait and local preference used to influence traffic leaving you. 00:54:16.000 --> 00:54:20.000 That's what I want you to take away from that. 00:54:20.000 --> 00:54:23.000 All right. 00:54:23.000 --> 00:54:25.000 Be prepared for those on the exam, folks.