WEBVTT 00:00:00.000 --> 00:00:09.760 So, let's begin our First Hop Redundancy Protocol discussion with an overview of what First 00:00:09.760 --> 00:00:16.680 Hop Redundancy Protocols are, and then we'll dive into HSRP specifically, VRP specifically, 00:00:16.680 --> 00:00:20.000 as well as GLBP specifically. 00:00:20.000 --> 00:00:25.959 So, why do we need First Hop Redundancy Protocols? 00:00:25.959 --> 00:00:30.600 Well, so far, what do we have here? 00:00:30.600 --> 00:00:33.700 We have three different VLANs. 00:00:33.700 --> 00:00:43.840 We have VLAN10 in our case, VLAN20 in our case, VLAN50 in our case, as well as VLAN200. 00:00:43.840 --> 00:00:51.119 We have our default gateways right now set up as Distribution 1 and Distribution 2. 00:00:51.119 --> 00:00:54.880 So, for example, let's just focus on VLAN10. 00:00:54.880 --> 00:01:04.320 We have interface VLAN10 here in our environment, and we configured it with 10.0.0.1 two sessions 00:01:04.320 --> 00:01:06.320 ago. 00:01:06.320 --> 00:01:11.279 And we configured this one with 10.0.0.2. 00:01:11.279 --> 00:01:22.480 So, the question now is, which one of those addresses do I give to our PCs in VLAN10 as 00:01:22.519 --> 00:01:26.519 their default gateway? 00:01:26.519 --> 00:01:33.519 Well, you'll see here we have 10.0.0.1 configured. 00:01:33.519 --> 00:01:39.519 Now, is it possible for us to provide both addresses? 00:01:39.519 --> 00:01:40.519 Sure. 00:01:40.519 --> 00:01:41.519 It is possible. 00:01:41.519 --> 00:01:50.519 For example, if we look at this output here, we'll see that we have configured our PC in 00:01:50.559 --> 00:01:54.559 its TCPIP settings with two default gateways. 00:01:54.559 --> 00:02:01.839 So, we're relying on the PC to be able to figure out who the default gateway is. 00:02:01.839 --> 00:02:06.879 Well, if both of them are running, that's pretty easy. 00:02:06.879 --> 00:02:13.919 But what if PC1 chooses to use DSW1 and DSW1 fails? 00:02:13.919 --> 00:02:17.160 How is it going to know to use DSW2? 00:02:17.160 --> 00:02:18.240 It's not. 00:02:18.240 --> 00:02:19.320 That's the thing. 00:02:19.320 --> 00:02:21.320 It's not going to know. 00:02:21.320 --> 00:02:24.279 So, what does that mean? 00:02:24.279 --> 00:02:29.160 PC1 keeps sending traffic to DSW1 even though it's not available. 00:02:29.160 --> 00:02:30.160 And what happens to it? 00:02:30.160 --> 00:02:31.160 It simply just disappears. 00:02:31.160 --> 00:02:32.160 It drops. 00:02:32.160 --> 00:02:34.919 It doesn't get there. 00:02:34.919 --> 00:02:47.520 So, we can't rely on the software settings of our end-user devices in order to get redundancy 00:02:47.520 --> 00:02:49.240 when it comes to the default gateway. 00:02:49.240 --> 00:02:52.080 It just doesn't work as we want it to. 00:02:52.080 --> 00:02:57.479 We would have to rely on things like the ARP cache timing out. 00:02:57.479 --> 00:03:02.600 And then when PC1 tries to get the MAC address of DSW1, it doesn't work. 00:03:02.600 --> 00:03:04.240 So, then it goes after DSW2. 00:03:04.240 --> 00:03:07.080 So, you see the challenges we face here? 00:03:07.080 --> 00:03:13.880 It could take hours, days maybe, before PC1 starts using the other default gateway. 00:03:13.880 --> 00:03:16.080 So, it's not going to work. 00:03:16.080 --> 00:03:18.679 So, instead, what do we do? 00:03:19.119 --> 00:03:27.119 We implement a feature, a service, on our distribution layer switches of first top redundancy 00:03:27.119 --> 00:03:28.119 protocol. 00:03:28.119 --> 00:03:36.759 And when we do so, we have the opportunity now to take these two physical devices and 00:03:36.759 --> 00:03:41.800 create a virtual default gateway. 00:03:42.119 --> 00:03:48.759 So, both DSW1 and DSW2 are physical multi-layer switches. 00:03:48.759 --> 00:03:52.639 But what we're going to do is we're going to run a first top redundancy protocol and 00:03:52.639 --> 00:04:04.639 now there is a virtual default gateway that both of them can use, both of them are responsible 00:04:04.639 --> 00:04:05.639 for. 00:04:05.639 --> 00:04:08.000 So, you'll see here this works with routers. 00:04:08.000 --> 00:04:10.639 This works with layer 3 switches. 00:04:10.639 --> 00:04:11.639 And what are we doing? 00:04:12.479 --> 00:04:14.279 We're creating a group. 00:04:14.279 --> 00:04:16.200 And when we create this group, what do we do? 00:04:16.200 --> 00:04:19.399 We put the physical switches in that group. 00:04:19.399 --> 00:04:21.559 So, I put DSW1 in that group. 00:04:21.559 --> 00:04:25.000 I put DSW2 in that group. 00:04:25.000 --> 00:04:32.839 And then this virtual default gateway is created for us and it creates the illusion of a single 00:04:32.839 --> 00:04:34.600 default gateway. 00:04:34.600 --> 00:04:39.320 So, this virtual router now is that default gateway. 00:04:39.519 --> 00:04:44.079 And you'll see there's an IP address in that subnet specifically. 00:04:44.079 --> 00:04:50.440 So, when you're creating your group, you're creating it for a specific subnet. 00:04:50.440 --> 00:04:55.440 So, in this case, subnet 10.0.0.0.24. 00:04:55.440 --> 00:04:59.959 I'm creating a virtual router with the IP address 10.0.0.0.254. 00:04:59.959 --> 00:05:03.920 You can use any IP address you want as long as it's not an IP address that's already being 00:05:03.920 --> 00:05:06.200 used in that subnet. 00:05:07.200 --> 00:05:11.200 So, in this case, I chose 10.0.0.24, 254. 00:05:11.200 --> 00:05:16.959 But it could be anything you want as long as it's not being used by anyone else. 00:05:16.959 --> 00:05:24.000 When you do that, a MAC address will also be created for that virtual router as you 00:05:24.000 --> 00:05:25.959 can see here. 00:05:25.959 --> 00:05:31.559 So, the IP address is shared between these two physical routers. 00:05:31.559 --> 00:05:34.679 The MAC address is now shared between these two physical routers. 00:05:34.679 --> 00:05:41.119 And it is this IP address in this MAC address that is going to be given to our end station. 00:05:41.119 --> 00:05:45.480 So, no longer are we going to be using the IP addresses of the interfaces. 00:05:45.480 --> 00:05:50.399 We're going to use the IP address of this virtual default gateway instead. 00:05:50.399 --> 00:05:52.920 And that's what we train our devices about. 00:05:52.920 --> 00:05:55.399 So, you could put that in your DHCP pool. 00:05:55.399 --> 00:06:01.720 So, when you create your DHCP pool for that subnet, that VLAN, that broadcast domain, 00:06:01.720 --> 00:06:05.239 we put that IP address in there as the default gateway for that pool. 00:06:05.239 --> 00:06:07.799 And that's what's given to your clients. 00:06:07.799 --> 00:06:13.399 And so, now you'll see if you look at our ARP cache here, 10.0.0.254 is the ARP cache 00:06:13.399 --> 00:06:14.399 for PC1. 00:06:14.399 --> 00:06:20.559 You'll see that we have that MAC address that has been returned to us in this particular 00:06:20.559 --> 00:06:21.559 case. 00:06:21.559 --> 00:06:27.640 So, now that we've done this, what happens? 00:06:27.640 --> 00:06:34.440 Well, it depends on the first top redundancy protocol that's being utilized. 00:06:34.440 --> 00:06:38.720 If you're using HSRP or VRRP, what I'm about to show you is 100% true. 00:06:38.720 --> 00:06:41.880 But if you're using GLBP, it's not 100% true. 00:06:41.880 --> 00:06:45.799 We'll talk about GLBP later in its own discussion, and you'll see it's slightly different. 00:06:45.799 --> 00:06:49.959 But for HSRP and VRRP, this is essentially what happens. 00:06:49.959 --> 00:06:58.000 One device, one of these physical routers, DSW1 or DSW2, is going to have to be responsible 00:06:58.000 --> 00:07:03.079 for everything in relation to this IP address and this MAC address. 00:07:03.079 --> 00:07:06.480 So, for HSRP, we call it active and standby. 00:07:06.480 --> 00:07:09.040 So, the active router is responsible for everything. 00:07:09.040 --> 00:07:11.440 The standby router is just standing by. 00:07:11.440 --> 00:07:15.959 With VRRP, we call it master and backup. 00:07:16.279 --> 00:07:22.959 So, these routers have an election process. 00:07:22.959 --> 00:07:24.920 They figure out who's who. 00:07:24.920 --> 00:07:30.679 The active router is now going to be the one that is responsible for forwarding traffic. 00:07:30.679 --> 00:07:36.000 So, it is the physical default gateway responsible for that IP address, responsible for that 00:07:36.000 --> 00:07:37.000 MAC address. 00:07:37.000 --> 00:07:39.959 It's going to respond to ARP requests. 00:07:39.959 --> 00:07:51.359 So, for example, when PC1 sends out an ARP request, give me the MAC address of this IP 00:07:51.359 --> 00:07:52.359 address. 00:07:52.359 --> 00:08:00.359 Even if the standby device gets it, it ignores it, and DSW1 is the one who responds back 00:08:00.359 --> 00:08:04.359 because it's active, therefore, that's how we get that. 00:08:04.359 --> 00:08:10.320 In addition, the active router has to train the MAC address tables of all the other devices. 00:08:10.320 --> 00:08:15.839 So, when it becomes the active router, it sends out what is called a GARP, a gratuitous 00:08:15.839 --> 00:08:21.320 ARP, which is an ARP reply that never had an associated ARP request with it first. 00:08:21.320 --> 00:08:25.440 So, I'm just sending out a GARP, and what that's going to do is it's going to train 00:08:25.440 --> 00:08:35.520 ASW1, the MAC address, and the port, and, of course, the VLAN. 00:08:35.520 --> 00:08:42.479 So, now ASW1 is pointing this way to that particular MAC address. 00:08:42.479 --> 00:08:46.359 So, with this switch, it would point this way. 00:08:46.359 --> 00:08:51.520 So, with DSW2, it would more than likely point that way. 00:08:51.520 --> 00:08:59.039 Those are Layer 2 links instead of Layer 3 because DSW1 is our current default gateway 00:08:59.039 --> 00:09:01.679 for that IP address and that MAC address. 00:09:01.679 --> 00:09:06.919 So, all traffic right now for that VLAN is flowing this way. 00:09:06.919 --> 00:09:11.119 So, what happens, though, if DSW1 fails? 00:09:11.119 --> 00:09:16.840 Well, we have to realize that every three seconds, by default, these devices are talking 00:09:16.840 --> 00:09:17.840 to each other. 00:09:17.840 --> 00:09:19.760 They're talking to each other. 00:09:19.760 --> 00:09:23.119 They're constantly updating each other about whether they are there or not. 00:09:23.119 --> 00:09:31.440 So, if the active device fails, then this device will no longer hear from DSW1. 00:09:31.440 --> 00:09:40.400 So, eventually, 10 seconds with HSRP, this device would be like, oh, you are really no 00:09:40.400 --> 00:09:41.559 longer there. 00:09:41.559 --> 00:09:44.559 So, I now have to become active. 00:09:44.559 --> 00:09:49.960 So, I become the active device, and then what do I do? 00:09:49.960 --> 00:09:55.840 I have to send a GARP out. 00:09:55.840 --> 00:09:57.760 Why am I sending a GARP out? 00:09:57.760 --> 00:10:00.719 I'm sending a GARP out so I can update the switches. 00:10:00.719 --> 00:10:04.359 So, now look at ASW1's MAC address table. 00:10:04.359 --> 00:10:10.280 The MAC address table now says, hey, it's out port channel 13. 00:10:10.280 --> 00:10:11.280 It's this way. 00:10:11.280 --> 00:10:13.039 So, what does that mean? 00:10:13.039 --> 00:10:16.400 That means all the user's traffic was flowing this way. 00:10:16.400 --> 00:10:21.359 As soon as this failed, by default, within 10 seconds, the user's traffic starts flowing 00:10:21.359 --> 00:10:22.359 this way. 00:10:22.359 --> 00:10:27.719 Now, 10 seconds seems like a long time, and it is, but you can absolutely fine-tune the 00:10:27.719 --> 00:10:37.520 timers of HSRP so you can get sub-second convergence, which is highly recommended that you do. 00:10:37.520 --> 00:10:45.520 And then, depending on how we configure the environment, when DSW1 recovers, for whatever 00:10:45.520 --> 00:10:49.039 reason, maybe we had to intervene, maybe it just magically rebooted itself, and now it's 00:10:49.039 --> 00:10:54.599 back online, what will happen is if we've configured it to do this, it will then take 00:10:54.599 --> 00:10:56.479 over that active role again. 00:10:56.479 --> 00:11:03.559 So, it takes over that active role, sends out the GARP onto the network so the MAC address 00:11:03.559 --> 00:11:12.919 tables can be adjusted, so now ASW1 is going to be pointing this way again, and so now 00:11:12.919 --> 00:11:16.440 the traffic just simply starts flowing this way again. 00:11:16.440 --> 00:11:22.919 And in this case, because the transition is so fast, and it's going to happen, this device 00:11:22.919 --> 00:11:26.640 comes up, it's like, okay, I'm up, all right, I'm going to take over the role, then typically 00:11:26.640 --> 00:11:30.119 there is no traffic loss at all when you recover back over. 00:11:30.119 --> 00:11:37.400 There may be a packet or two that goes missing when you've got a failover to DSW2, or a TCP 00:11:37.400 --> 00:11:41.119 that will auto-recover for you, so that's not a big deal. 00:11:41.119 --> 00:11:45.880 Even a voice conversation, not a big deal either, a packet or two for a voice conversation. 00:11:45.880 --> 00:11:48.440 Human beings will just be like, oh, sorry, I missed that, can you repeat that? 00:11:48.440 --> 00:11:50.200 You'll be fine, you'll be fine, right? 00:11:50.200 --> 00:11:51.200 See how amazing this is? 00:11:51.200 --> 00:11:53.200 This is awesome stuff. 00:11:53.200 --> 00:11:55.760 But there's something you've got to think about, and it's something we brought to your 00:11:55.760 --> 00:11:58.460 attention in every single session so far. 00:11:58.460 --> 00:12:06.380 Other services and features have effects on other services and features here. 00:12:06.380 --> 00:12:10.659 And so, one of the things we have to consider is spanning tree protocol. 00:12:10.659 --> 00:12:11.659 Spanning tree protocol. 00:12:11.659 --> 00:12:17.059 Think about it this way, if this is our root bridge for VLAN10, then what port would be 00:12:17.059 --> 00:12:18.059 the root port? 00:12:18.059 --> 00:12:22.700 It would be this port right here, and this would be blocked, and this would be blocked. 00:12:22.700 --> 00:12:24.299 That would be a problem. 00:12:24.299 --> 00:12:25.500 Why would that be a problem? 00:12:25.500 --> 00:12:28.099 Because remember, this is the default gateway. 00:12:28.739 --> 00:12:32.659 So what would happen is traffic would end up flowing this way, flowing this way, and 00:12:32.659 --> 00:12:38.700 flowing out. 00:12:38.700 --> 00:12:42.059 You see the problem? 00:12:42.059 --> 00:12:45.580 You don't want traffic to flow like that. 00:12:45.580 --> 00:12:55.380 So it's always imperative that your root bridge is the same device as the default gateway. 00:12:55.380 --> 00:12:59.140 And therefore, your secondary root bridge should always be the same device that's going 00:12:59.140 --> 00:13:01.580 to be your standby. 00:13:01.580 --> 00:13:07.700 That way there, when you have a failover, both the root bridge and this device, the 00:13:07.700 --> 00:13:09.940 root bridge goes here, and this becomes active. 00:13:09.940 --> 00:13:14.460 When it fails back, it returns back to normal. 00:13:14.460 --> 00:13:16.099 And this could get even worse for you. 00:13:16.099 --> 00:13:17.700 Let's say, for example, this was the default. 00:13:17.700 --> 00:13:21.299 No, let's say this was the default gateway here. 00:13:21.299 --> 00:13:24.179 Let's say this was the root bridge down here. 00:13:24.179 --> 00:13:27.580 Let's say this was the root port here, and this was blocked, blocked, blocked, blocked. 00:13:27.580 --> 00:13:30.260 This was blocked, blocked, blocked. 00:13:30.260 --> 00:13:35.859 It is possible, based on this topology, it's possible that your traffic could actually 00:13:35.859 --> 00:13:38.940 flow like this. 00:13:38.940 --> 00:13:43.700 And that's why, when we were talking about making sure your root bridge for Spanning 00:13:43.700 --> 00:13:49.780 Tree Protocol is in the right place, it's not just for the sake of Spanning Tree Protocol, 00:13:49.780 --> 00:13:54.020 it's for the sake of other services as well that you're depending on. 00:13:54.859 --> 00:13:59.539 So, understand the dependencies, understand the gotchas with different protocols, is going 00:13:59.539 --> 00:14:04.940 to be a key critical thing for you in the real world, so you can make better decisions 00:14:04.940 --> 00:14:07.700 about your network. 00:14:07.700 --> 00:14:11.539 So whenever you're working with a service going forward, always ask yourself, how does 00:14:11.539 --> 00:14:14.500 this service affect my other services that I have running right now? 00:14:25.020 --> 00:14:32.580 So, line up your Spanning Tree root bridge with your active forwarder at all times. 00:14:32.580 --> 00:14:37.020 So, you want to be in complete control over all of this. 00:14:37.020 --> 00:14:46.099 So, some things to keep in mind is that for every subnet, you're going to have to have 00:14:46.099 --> 00:14:47.099 a group. 00:14:47.099 --> 00:14:52.539 So, you can't have two different subnets in one group, okay? 00:14:52.539 --> 00:14:57.020 So, you are going to have essentially a group for each and every single subnet that you 00:14:57.020 --> 00:14:59.219 want to have the redundant default gateways. 00:14:59.219 --> 00:15:02.859 So, I would have a group for this subnet, I'd have a group for this subnet, I'd have 00:15:02.859 --> 00:15:08.140 a group for this subnet, and I'd have a group for this subnet, and you identify those groups 00:15:08.140 --> 00:15:09.859 by a group number. 00:15:09.859 --> 00:15:12.219 So, I could label these group 1, 2, 3, and 4. 00:15:12.219 --> 00:15:13.859 I can label them group 10, 20, 30, 40. 00:15:13.859 --> 00:15:18.440 I can label them any number within the numbering range that you're allowed, and it all depends 00:15:18.440 --> 00:15:23.200 on the version of first hop redundancy protocol that you're using. 00:15:23.200 --> 00:15:25.479 So, more on that later. 00:15:25.479 --> 00:15:29.559 And then every single one of those groups is going to have a different IP address and 00:15:29.559 --> 00:15:32.760 a different MAC address, and we'll talk more about that later. 00:15:32.760 --> 00:15:38.440 So, when you think about your multilayer switches, you're configuring this feature, this service 00:15:38.440 --> 00:15:39.440 on your SVIs. 00:15:39.440 --> 00:15:44.719 That's what we're going to be configuring it on, our SVIs. 00:15:44.719 --> 00:15:49.080 And so, we'd configure it on the SVIs here, we'd configure it on the SVIs here, and we'd 00:15:49.080 --> 00:15:52.479 have to make sure that the parameters that need to match, match perfectly, or it's not 00:15:52.479 --> 00:15:53.479 going to work for us. 00:15:53.479 --> 00:15:54.479 All right. 00:15:54.479 --> 00:15:55.479 What if you were using routers? 00:15:55.479 --> 00:15:59.520 Let's say I had a router here, let's say I had a router here, we had two routers connected 00:15:59.520 --> 00:16:05.719 to a switch, we had all of our user PCs down here. 00:16:05.719 --> 00:16:11.039 Then we'd be doing it on the physical interface, the physical interface. 00:16:11.760 --> 00:16:14.760 So, it's the default gateway for that subnet. 00:16:14.760 --> 00:16:16.200 All right. 00:16:16.200 --> 00:16:17.200 What about subinterfaces? 00:16:17.200 --> 00:16:19.479 Well, then you'd be configuring it on the subinterfaces. 00:16:19.479 --> 00:16:25.200 So, if you had subinterfaces instead, then you'd be creating it on the subinterfaces. 00:16:25.200 --> 00:16:27.239 So, make sure you're aware of that for the exam. 00:16:27.239 --> 00:16:30.559 So, if it's a diagram of two routers with subinterfaces, you're configuring it on the 00:16:30.559 --> 00:16:31.559 subinterfaces. 00:16:31.559 --> 00:16:34.719 If it's a diagram with just two physical interfaces, no subinterfaces, then you're configuring 00:16:34.719 --> 00:16:35.719 it on the physical interfaces. 00:16:35.719 --> 00:16:38.640 If it's a multi-layer switch, then you're configuring it on the SVIs. 00:16:38.640 --> 00:16:39.640 All right. 00:16:39.640 --> 00:16:44.039 So, these are the three different protocols we're going to have to know for the certification 00:16:44.039 --> 00:16:45.039 exam. 00:16:45.039 --> 00:16:48.239 Hot standby router protocol. 00:16:48.239 --> 00:16:53.320 This is Cisco proprietary first top redundancy protocol. 00:16:53.320 --> 00:17:02.760 It is the first, meaning this came out before the industry standard version of a first top 00:17:02.760 --> 00:17:04.119 redundancy protocol. 00:17:04.520 --> 00:17:09.119 So, we'll learn about that here today. 00:17:09.119 --> 00:17:14.119 Provides redundant gateways where one is active, one is standby. 00:17:14.119 --> 00:17:19.119 VRRP is the industry standard ripoff of HSRP. 00:17:19.119 --> 00:17:23.719 So, here's a little bit of history lesson. 00:17:23.719 --> 00:17:25.640 Cisco created HSRP. 00:17:25.640 --> 00:17:28.219 It was used on Cisco devices. 00:17:28.219 --> 00:17:30.479 Other vendors out there wanted that feature. 00:17:30.479 --> 00:17:36.079 So, Cisco actually licensed it to other vendors for a fee. 00:17:36.079 --> 00:17:44.280 So, it was implemented on other vendors' equipment, but they had to pay Cisco a fee. 00:17:44.280 --> 00:17:51.359 Eventually, the industry banded together and created VRRP, an industry standard version 00:17:51.359 --> 00:17:57.079 of HSRP, so that way they could stop paying Cisco. 00:17:57.079 --> 00:18:02.640 But in the end, it behaves the same way with a few minor differences that really don't 00:18:02.640 --> 00:18:03.640 matter. 00:18:03.640 --> 00:18:04.640 Okay? 00:18:04.640 --> 00:18:10.239 And then we got GLVP, which is Cisco proprietary, but this is cool. 00:18:10.239 --> 00:18:12.920 This is so cool. 00:18:12.920 --> 00:18:19.439 Provides you the ability to use all your default gateways for a single subnet, all right? 00:18:19.439 --> 00:18:21.040 So, let's be clear here. 00:18:21.040 --> 00:18:28.280 For this one and this one, you can only use one physical device at a time per subnet. 00:18:28.280 --> 00:18:34.760 Meaning, for example, this could be active for this subnet, but we could have this one 00:18:34.760 --> 00:18:36.000 active for this subnet. 00:18:36.000 --> 00:18:37.000 That would be okay. 00:18:37.000 --> 00:18:40.280 So, we could do like active, standby, active, standby. 00:18:40.280 --> 00:18:41.280 This one could be active. 00:18:41.280 --> 00:18:42.920 This one could be standby. 00:18:42.920 --> 00:18:45.959 This could be standby, let's say, and this could be active here, all right? 00:18:45.959 --> 00:18:53.520 So, we have the ability to use both at the same time as default gateways, so remember 00:18:53.520 --> 00:19:01.560 when we were looking at our spanning tree protocol discussion yesterday, and it was 00:19:01.560 --> 00:19:08.280 about manipulating the convergence of spanning tree protocol, that's what it was. 00:19:08.280 --> 00:19:15.800 And we looked at this topology here, so I could have this as the active forwarder for 00:19:15.800 --> 00:19:19.719 VLAN 10, and this could be the active forwarder for VLAN 50. 00:19:19.719 --> 00:19:20.719 That's not a problem at all. 00:19:20.719 --> 00:19:29.599 I can do that, but you can only have one physical device active at a time for that subnet slash 00:19:29.599 --> 00:19:31.319 VLAN, right? 00:19:31.319 --> 00:19:35.439 So, with GLBP, I can have up to four. 00:19:35.439 --> 00:19:44.560 I can have up to four devices active at the same time, meaning forwarding traffic all 00:19:44.560 --> 00:19:45.920 at the same time. 00:19:45.920 --> 00:19:51.160 So, in this case, for example, we have VLAN 10 here, if you remember. 00:19:51.160 --> 00:19:58.160 So, does that mean that PC1's traffic could go this way, and let's say PC2's traffic could 00:19:58.160 --> 00:19:59.959 go this way? 00:19:59.959 --> 00:20:00.959 Absolutely. 00:20:00.959 --> 00:20:01.959 Absolutely. 00:20:01.959 --> 00:20:08.439 That's what GLBP lets me do, but now you have to think about spanning tree protocol. 00:20:08.439 --> 00:20:11.000 Spanning tree protocol doesn't like GLBP. 00:20:11.000 --> 00:20:13.959 GLBP doesn't like spanning tree protocol. 00:20:13.959 --> 00:20:14.959 Why? 00:20:14.959 --> 00:20:20.959 Because if this was my topology right now, and this is my layer two, layer three environment, 00:20:20.959 --> 00:20:26.640 so this is all layer two, this is all layer three, as we've seen before, this would be, 00:20:26.640 --> 00:20:30.479 let's say, the root port block, block, block, right? 00:20:30.479 --> 00:20:32.520 For spanning tree protocol. 00:20:32.520 --> 00:20:34.160 What does that mean? 00:20:34.160 --> 00:20:39.439 It means that everyone has to go this way anyways, and then you would end up with traffic 00:20:39.439 --> 00:20:40.439 flow like this. 00:20:40.439 --> 00:20:41.520 This is silly. 00:20:41.520 --> 00:20:43.400 You don't want this to happen. 00:20:43.400 --> 00:20:49.520 So, having a spanning tree topology like this, your layer two environment like this, doesn't 00:20:49.520 --> 00:20:52.000 play well with GLBP. 00:20:52.000 --> 00:20:57.280 What you actually need to do to get GLBP working is to change your layer two, layer 00:20:57.280 --> 00:20:58.280 three boundaries. 00:20:58.280 --> 00:20:59.599 So, do something like this. 00:20:59.599 --> 00:21:01.400 Now, this is all layer three. 00:21:01.400 --> 00:21:05.839 So, you see how the links between distribution one and two are there? 00:21:05.839 --> 00:21:06.839 Why? 00:21:06.839 --> 00:21:15.199 Because that changes how spanning tree protocol is going to block ports. 00:21:15.199 --> 00:21:19.800 Now, in this case, more than likely, if this is our root bridge, we're still going to end 00:21:19.800 --> 00:21:21.800 up here with a root port here. 00:21:21.800 --> 00:21:24.719 More than likely, these arrests are going to be blocked, because if you look, we still 00:21:24.719 --> 00:21:26.319 have a figure eight loop here. 00:21:26.319 --> 00:21:29.119 So, now that requires you to do filtering, right? 00:21:29.119 --> 00:21:38.599 So, if you filter and you say 10 and 20 are allowed here, and 50 and 20 are allowed here, 00:21:38.599 --> 00:21:44.280 and 10 and 20 are allowed here, and 50 and 20 are allowed here, what does that mean? 00:21:44.280 --> 00:21:45.280 Okay? 00:21:45.280 --> 00:21:51.520 So, that means now, in this particular case, that for VLAN 10, these are the only two links 00:21:51.520 --> 00:21:53.439 in VLAN 10 right now, right? 00:21:53.439 --> 00:21:58.160 So, there is no loop, because you've done your filtering, which means that this would 00:21:58.160 --> 00:22:03.400 be a root port, and then we would have a designated port here. 00:22:03.400 --> 00:22:05.760 We'd have a – nope, this would be blocked on this one. 00:22:05.760 --> 00:22:08.479 This would be blocked here, and you might have something like that. 00:22:08.479 --> 00:22:12.800 So, now that you have something like that, because you've done filtering and changed 00:22:12.800 --> 00:22:16.959 your layer three, layer two boundary, now all of a sudden, you can use GLBP. 00:22:16.959 --> 00:22:20.719 So, there's another great example of how, if you don't understand how one technology 00:22:20.719 --> 00:22:25.719 works, you could be messing up your other technology, and a lot of people end up in 00:22:25.719 --> 00:22:31.199 a situation where they implement GLBP, because they read about it, they think it's awesome, 00:22:31.199 --> 00:22:32.680 which it absolutely is. 00:22:32.680 --> 00:22:38.040 There's no denying that, but they have their network set up like this, they implement GLBP, 00:22:38.040 --> 00:22:41.319 and they don't realize that all their traffic is doing this. 00:22:41.560 --> 00:22:44.959 Well, then you might as well use – if that's what you're going to leave it as, you might 00:22:44.959 --> 00:22:49.160 as well just use HSRP, because with HSRP, at least your traffic would do that. 00:22:51.400 --> 00:22:54.760 So, these are the things you just got to be careful of in the real world when you're using 00:22:54.760 --> 00:22:57.000 these technologies or learning about them. 00:22:57.000 --> 00:23:03.800 It's about recognizing just some of the different little aspects about them that could make 00:23:03.800 --> 00:23:06.000 or break your environment when it's all said and done. 00:23:06.000 --> 00:23:07.000 All right. 00:23:07.000 --> 00:23:09.239 So, that's our introduction to first-hop redundancy protocols. 00:23:09.239 --> 00:23:12.359 Now, it's time to actually get into looking at HSRP.