WEBVTT 1 00:00.000 --> 00:03.840 So we still have a problem that we have to address. 2 00:03.840 --> 00:09.080 In a traditional network, we typically have a pair of distribution switches and 3 00:09.080 --> 00:09.600 these switches 4 00:09.600 --> 00:11.920 are going to run SVIs. 5 00:11.920 --> 00:17.390 These SVIs serve as our default gateways for all of the hosts that reside on a 6 00:17.390 --> 00:17.920 given 7 00:17.920 --> 00:18.920 subnet. 8 00:18.920 --> 00:23.450 And so logically speaking, we have hosts down here and they connect up to one 9 00:23.450 --> 00:24.060 of these 10 00:24.060 --> 00:26.240 SVIs as the default gateway. 11 00:26.240 --> 00:30.140 We run a first hop redundancy protocol between these to make sure we have WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 11 00:26.240 --> 00:30.140 We run a first hop redundancy protocol between these to make sure we have 12 00:30.140 --> 00:30.960 redundancy in 13 00:30.960 --> 00:33.520 case one of the distributions, which is goes down. 14 00:33.520 --> 00:38.260 And then every other subnet has something similar where we have a SVI on each 15 00:38.260 --> 00:38.480 one of 16 00:38.480 --> 00:41.640 these switches and they connect into a layer 2 domain. 17 00:41.640 --> 00:45.720 And the hosts off of these are serviced by those SVIs. 18 00:45.720 --> 00:50.200 Physically, we are talking about access switches that come down here. 19 00:50.200 --> 00:53.440 Maybe we have a port channel somehow. 20 00:53.440 --> 00:57.720 We were running VSS or a stackwise virtual, but either way, we have a layer 2 21 00:57.720 --> 00:58.480 connection 22 00:58.480 --> 01:04.060 down to an access switch and the hosts connect here on a particular VLAN, like WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 22 00:58.480 --> 01:04.060 down to an access switch and the hosts connect here on a particular VLAN, like 23 01:04.060 --> 01:05.240 VLAN 10, and 24 01:05.240 --> 01:09.840 then the trunk carries them up to the distribution layer. 25 01:09.840 --> 01:12.600 So this is the physical representation of what's happening. 26 01:12.600 --> 01:18.540 This is the logical representation, but either way, we have a redundant way for 27 01:18.540 --> 01:19.360 our hosts 28 01:19.360 --> 01:22.080 to connect to their default gateways. 29 01:22.080 --> 01:25.360 But now we have a very different story. 30 01:25.360 --> 01:30.820 We have a fabric where we have multiple edge nodes, potentially lots of edge WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 30 01:25.360 --> 01:30.820 We have a fabric where we have multiple edge nodes, potentially lots of edge 31 01:30.820 --> 01:31.600 nodes here. 32 01:31.600 --> 01:33.480 Let's just draw three for now. 33 01:33.480 --> 01:38.200 And we've said because of VXLAN, we can say that each one of these is 34 01:38.200 --> 01:39.480 connecting to the 35 01:39.480 --> 01:40.480 same VLAN. 36 01:40.480 --> 01:42.960 Let's say VLAN 10 in this case. 37 01:42.960 --> 01:46.620 And so we can kind of draw dotted lines in here, which indicates that this is a 38 01:46.620 --> 01:47.280 stretched 39 01:47.280 --> 01:48.280 subnet. 40 01:48.280 --> 01:53.440 And we've got VXLAN tunnels happening here on the back end to extend this out. 41 01:53.440 --> 01:56.080 And so I've got a host here on VLAN 10. 42 01:56.080 --> 01:57.760 I've got a host here on VLAN 10. 43 01:57.760 --> 01:59.320 A host over here. 44 01:59.320 --> 02:05.040 And these are all on the 10.10.0.0/24 subnet. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 44 01:59.320 --> 02:05.040 And these are all on the 10.10.0.0/24 subnet. 45 02:05.040 --> 02:06.760 So here's the question. 46 02:06.760 --> 02:11.200 Where do the SVIs and the default gateways live? 47 02:11.200 --> 02:14.320 Remember, this is a layer 3 fabric up here. 48 02:14.320 --> 02:19.120 We do have VXLAN tunnels, so we have layer 2 access among all of the switches. 49 02:19.120 --> 02:23.760 But when we're talking about the default gateway, where are we going to put it? 50 02:23.760 --> 02:27.310 I might put it here on this switch, and that's great for this host because it's 51 02:27.310 --> 02:27.900 physically 52 02:27.900 --> 02:30.760 attached to it or through it either way. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 52 02:27.900 --> 02:30.760 attached to it or through it either way. 53 02:30.760 --> 02:34.760 It has a direct access to its default gateway. 54 02:34.760 --> 02:36.440 But what about these hosts over here? 55 02:36.440 --> 02:42.000 So let's say this is the .1 IP address, or maybe .254 if we want to. 56 02:42.000 --> 02:46.030 And so we might say, OK, well, all of these are going to have to go through the 57 02:46.030 --> 02:47.160 VXLAN tunnel 58 02:47.160 --> 02:49.920 just to get to their default gateways. 59 02:49.920 --> 02:54.840 Well, what if we want to communicate with another VLAN here? 60 02:54.840 --> 02:57.320 Let's say that these are all connecting in. 61 02:57.320 --> 03:02.640 Actually, let's just draw it here, hanging off of this one switch, VLAN 20, and WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 61 02:57.320 --> 03:02.640 Actually, let's just draw it here, hanging off of this one switch, VLAN 20, and 62 03:02.640 --> 03:03.160 a host 63 03:03.160 --> 03:05.960 that is connecting in off the same switch. 64 03:05.960 --> 03:09.520 Two different VLANs require going through the default gateway. 65 03:09.520 --> 03:13.550 So in order for these two devices to communicate, the one on the left and VLAN 66 03:13.550 --> 03:14.560 10, the one 67 03:14.560 --> 03:19.840 on the right on VLAN 20, they're going to have to go over here to the default 68 03:19.840 --> 03:20.600 gateway and 69 03:20.600 --> 03:22.480 get switched over. 70 03:22.480 --> 03:28.020 And that even assumes that the VLAN 20 SVI exists over on that switch and can 71 03:28.020 --> 03:28.840 get routed 72 03:28.840 --> 03:30.360 between the two. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 72 03:28.840 --> 03:30.360 between the two. 73 03:30.360 --> 03:35.990 So we can tell that we've got a lot of problems if the SVI resides on a single 74 03:35.990 --> 03:36.960 switch. 75 03:36.960 --> 03:40.240 And again, specifically the default gateway. 76 03:40.240 --> 03:42.000 So what are we going to do here? 77 03:42.000 --> 03:45.880 Well, we're going to do away with this old model. 78 03:45.880 --> 03:50.500 We're going to get away from thinking about a single SVI on each switch and 79 03:50.500 --> 03:51.280 then we're 80 03:51.280 --> 03:54.880 running default gateways through them and FHRP's for redundancy. 81 03:54.880 --> 03:58.980 We're going to leave all of that behind and embrace a completely new 82 03:58.980 --> 04:00.240 methodology known WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 82 03:58.980 --> 04:00.240 methodology known 83 04:00.240 --> 04:03.800 as the anycast gateway. 84 04:03.800 --> 04:09.280 Anycast is a very interesting traffic type that we don't talk about quite as 85 04:09.280 --> 04:10.120 often as all 86 04:10.120 --> 04:17.690 the other casts, meaning we have Unicast and broadcast that we talk a whole lot 87 04:17.690 --> 04:18.000 about. 88 04:18.000 --> 04:21.800 And then we study multicast as well. 89 04:21.800 --> 04:27.280 And so we're either talking to one device or all devices or some devices. 90 04:27.280 --> 04:33.520 And you'd think that maybe that covers everything except we also have any cast. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 90 04:27.280 --> 04:33.520 And you'd think that maybe that covers everything except we also have any cast. 91 04:33.520 --> 04:41.110 And anycast says not one specific device, not all devices or some devices, but 92 04:41.110 --> 04:42.480 any eligible 93 04:42.480 --> 04:43.800 device. 94 04:43.800 --> 04:48.240 In other words, I don't care as long as somebody answers. 95 04:48.240 --> 04:53.040 So typically from a networking perspective, this is going to find the nearest 96 04:53.040 --> 04:53.920 resource that 97 04:53.920 --> 04:57.640 has a particular IP address, which has an implication. 98 04:57.640 --> 05:04.090 If I try to communicate with an anycast IP address like 10.1.1.1, well, if I'm WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 98 04:57.640 --> 05:04.090 If I try to communicate with an anycast IP address like 10.1.1.1, well, if I'm 99 05:04.090 --> 05:04.760 saying that 100 05:04.760 --> 05:08.440 there's a nearest one, that means there are other ones out there as well. 101 05:08.440 --> 05:10.400 There must be two or three of these. 102 05:10.400 --> 05:16.360 And so that means that we actually do have and support duplicate IP addresses 103 05:16.360 --> 05:16.720 out on the 104 05:16.720 --> 05:18.440 network. 105 05:18.440 --> 05:22.760 So what does this look like from a default gateway perspective? 106 05:22.760 --> 05:28.280 Well, what it looks like is now we throw an SVI, not just onto one of these 107 05:28.280 --> 05:29.360 switches, but 108 05:29.360 --> 05:33.800 onto every one of these switches for VLAN 10. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 108 05:29.360 --> 05:33.800 onto every one of these switches for VLAN 10. 109 05:33.800 --> 05:36.520 And then we could do the same for all the other SVIs. 110 05:36.520 --> 05:42.480 Furthermore, all of these are going to share the same IP address 10.10.0.1. 111 05:42.480 --> 05:45.120 We'll say is the default gateway. 112 05:45.120 --> 05:49.700 So all of these VLAN 10 hosts point to this IP address as their default gateway 113 05:49.700 --> 05:50.040 . 114 05:50.040 --> 05:51.720 We say, well, wait a second here. 115 05:51.720 --> 05:56.880 We have three different IP addresses that are all duplicates of one another. 116 05:56.880 --> 06:01.640 Which one are we going to talk to when we try to go to our default gateway? WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 116 05:56.880 --> 06:01.640 Which one are we going to talk to when we try to go to our default gateway? 117 06:01.640 --> 06:03.280 Well, the answer is right here. 118 06:03.280 --> 06:09.080 It is the nearest of our gateways or of our IP addresses. 119 06:09.080 --> 06:10.640 What's the nearest one? 120 06:10.640 --> 06:15.650 Well, the switch over on the left, this host, its nearest one is its directly 121 06:15.650 --> 06:16.360 attached 122 06:16.360 --> 06:17.360 switch. 123 06:17.360 --> 06:22.160 And this one over here is also its directly attached. 124 06:22.160 --> 06:26.200 And this one on the right also its directly attached switch. 125 06:26.200 --> 06:28.360 So we don't have to go very far. 126 06:28.360 --> 06:33.450 I just ARP, send an ARP for my default gateway and I'm going to get an ARP WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 126 06:28.360 --> 06:33.450 I just ARP, send an ARP for my default gateway and I'm going to get an ARP 127 06:33.450 --> 06:35.200 response back 128 06:35.200 --> 06:38.400 from the appropriate switch. 129 06:38.400 --> 06:42.040 The namely, the first one that sees my ARP request. 130 06:42.040 --> 06:45.640 Which means that all three of these hosts are using different default gateways 131 06:45.640 --> 06:45.920 even 132 06:45.920 --> 06:49.280 though they all have the same IP address. 133 06:49.280 --> 06:52.680 So is this a problem? 134 06:52.680 --> 06:55.280 And the answer is no. 135 06:55.280 --> 06:57.960 In fact, it's a wonderful solution. 136 06:57.960 --> 07:00.400 It doesn't cause additional problems. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 136 06:57.960 --> 07:00.400 It doesn't cause additional problems. 137 07:00.400 --> 07:09.080 It allows us to find a default gateway on the local edge node. 138 07:09.080 --> 07:13.060 Whatever my local edge node is, whether I connect to it directly, whether I 139 07:13.060 --> 07:13.800 connect through 140 07:13.800 --> 07:18.920 it, maybe I've got a series of switches that connect to this edge node. 141 07:18.920 --> 07:20.960 And so I'm a host hanging out here. 142 07:20.960 --> 07:26.800 Well, the first IP address that I find that fits my default gateway IP is going 143 07:26.800 --> 07:27.520 to be 144 07:27.520 --> 07:34.000 this switch here that's in the path, or before I hit that fabric and get onto WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 144 07:27.520 --> 07:34.000 this switch here that's in the path, or before I hit that fabric and get onto 145 07:34.000 --> 07:35.880 the SDA world. 146 07:35.880 --> 07:41.550 Furthermore, I'm going to be able to do local switching now, local SVI 147 07:41.550 --> 07:42.760 switching. 148 07:42.760 --> 07:47.280 So if I need to communicate with hosts, let's draw it over here. 149 07:47.280 --> 07:50.360 So I've got two different edge fabric switches. 150 07:50.360 --> 07:52.880 These are both edge switches. 151 07:52.880 --> 07:58.720 They both connect into the fabric. 152 07:58.720 --> 08:05.960 And I have SVI's for VLANs 10 and 20 on both of these. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 152 07:58.720 --> 08:05.960 And I have SVI's for VLANs 10 and 20 on both of these. 153 08:05.960 --> 08:07.640 And they're both running any cast. 154 08:07.640 --> 08:11.780 So the IP address for the SVI for 10 is the same on both of these switches, 155 08:11.780 --> 08:13.040 same thing for 156 08:13.040 --> 08:14.320 the 20s. 157 08:14.320 --> 08:20.700 So if I now have a host on VLAN 10 and we need to communicate to the host on V 158 08:20.700 --> 08:22.040 LAN 20, well, 159 08:22.040 --> 08:24.080 I can stay on my local switch. 160 08:24.080 --> 08:25.560 I hit my default gateway. 161 08:25.560 --> 08:30.780 It gets layer 3 switched, you know, change colors, layer 3 switched over to the WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 161 08:25.560 --> 08:30.780 It gets layer 3 switched, you know, change colors, layer 3 switched over to the 162 08:30.780 --> 08:31.080 SVI for 163 08:31.080 --> 08:33.720 VLAN 20 and then sent down. 164 08:33.720 --> 08:38.440 Well, what about this switch over here? 165 08:38.440 --> 08:40.300 What if I have the exact same thing at the exact same time except now it's two 166 08:40.300 --> 08:41.000 different hosts 167 08:41.000 --> 08:43.840 that are connected to the same two VLANs? 168 08:43.840 --> 08:45.000 Well, same thing here. 169 08:45.000 --> 08:47.080 I send traffic up. 170 08:47.080 --> 08:51.050 It hits the default gateway, gets switched over to the local SVI and then 171 08:51.050 --> 08:52.120 forwarded down 172 08:52.120 --> 08:54.760 VLAN 20 at layer 2. 173 08:54.760 --> 08:59.190 Both of these operations are happening at the same time and they stay within 174 08:59.190 --> 08:59.840 the fabric 175 08:59.840 --> 09:00.840 edge switch. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 175 08:59.840 --> 09:00.840 edge switch. 176 09:00.840 --> 09:05.160 You have to go through the VXLAN tunnels and trombone traffic back and forth. 177 09:05.160 --> 09:06.680 That is not required. 178 09:06.680 --> 09:11.020 We can stay on our local switches and furthermore, if I do need to leave the 179 09:11.020 --> 09:11.760 subnet and get 180 09:11.760 --> 09:13.120 routed out somewhere. 181 09:13.120 --> 09:18.790 Well, at this point, I'm going to hit my local SVI and then we'll enter into 182 09:18.790 --> 09:19.920 the SDA world 183 09:19.920 --> 09:25.240 where I'm referencing list information and I'm getting encapsulated into VXLAN. 184 09:25.240 --> 09:28.360 So either way, my gateways are always going to be local. 185 09:28.360 --> 09:33.690 I'm going to have the same IP addresses and the same SVI's configured on all of WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 185 09:28.360 --> 09:33.690 I'm going to have the same IP addresses and the same SVI's configured on all of 186 09:33.690 --> 09:34.360 my edge 187 09:34.360 --> 09:36.800 switches, wherever those VLANs exist. 188 09:36.800 --> 09:41.440 And importantly, we're going to deploy no FHRP's. 189 09:41.440 --> 09:45.730 Those aren't going to be needed because our redundancy is built using any cast 190 09:45.730 --> 09:46.000 rather 191 09:46.000 --> 09:49.790 than having any other kind of sophisticated method for trying to share a 192 09:49.790 --> 09:50.880 default gateway.