WEBVTT 1 00:00.000 --> 00:04.880 One of the goals of diving deeper into the world of routing and switching is to 2 00:04.880 --> 00:05.160 become 3 00:05.160 --> 00:08.040 one with layer two and layer three. 4 00:08.040 --> 00:11.800 It's a little phrase I say because it just sounds funny to say one, two, three 5 00:11.800 --> 00:12.400 like that, 6 00:12.400 --> 00:16.690 but we have to become one with layer two and layer three and understand how 7 00:16.690 --> 00:17.360 they come 8 00:17.360 --> 00:18.360 together. 9 00:18.360 --> 00:22.390 So, our focus right now is on layer two, but VLANs are absolutely intertwined 10 00:22.390 --> 00:23.000 with layer 11 00:23.000 --> 00:24.120 three technologies. 12 00:24.120 --> 00:29.820 Our VLAN interface is default, gateways, subnets, all of this really could fall 13 00:29.820 --> 00:30.600 into the layer WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 13 00:29.820 --> 00:30.600 into the layer 14 00:30.600 --> 00:35.680 three category, but it's built on layer two and VLANs. 15 00:35.680 --> 00:40.290 And so when we start to draw topologies, usually we're talking about drawing 16 00:40.290 --> 00:40.820 physical 17 00:40.820 --> 00:42.720 switches and their connections. 18 00:42.720 --> 00:46.400 Maybe this is an ether channel between these switches and they connect down to 19 00:46.400 --> 00:46.960 this other 20 00:46.960 --> 00:50.450 switch and we'll draw plenty of these types of diagrams when we're looking at 21 00:50.450 --> 00:50.960 spanning 22 00:50.960 --> 00:59.410 tree and the like, but this is a physical drawing that shows me which links are 23 00:59.410 --> 01:00.640 connected WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 23 00:59.410 --> 01:00.640 connected 24 01:00.640 --> 01:04.880 to which devices and which devices are connected to other devices and how they 25 01:04.880 --> 01:05.920 're connected. 26 01:05.920 --> 01:10.840 But this doesn't tell me anything about layer two, it doesn't tell me anything 27 01:10.840 --> 01:11.600 about layer 28 01:11.600 --> 01:14.640 three at least natively. 29 01:14.640 --> 01:19.400 And so this is where I like to try to inject a little bit more information as 30 01:19.400 --> 01:20.080 far as how 31 01:20.080 --> 01:21.760 to read a diagram here. 32 01:21.760 --> 01:26.120 For example, are these links layer two or are these links layer three? 33 01:26.120 --> 01:31.080 And we can kind of start to get around some of that if we put more details into WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 33 01:26.120 --> 01:31.080 And we can kind of start to get around some of that if we put more details into 34 01:31.080 --> 01:32.280 our drawings. 35 01:32.280 --> 01:37.120 For example, whenever I draw topologies, I like to use a dot to represent a 36 01:37.120 --> 01:37.960 layer three 37 01:37.960 --> 01:39.800 interface. 38 01:39.800 --> 01:45.590 This is something that I've done pretty much ever since I got my CCNP and I 39 01:45.590 --> 01:46.480 started doing 40 01:46.480 --> 01:50.590 additional studying to go deeper was recognizing that some of these interfaces 41 01:50.590 --> 01:51.400 might be layer 42 01:51.400 --> 01:54.640 two, but some of them might be layer three. 43 01:54.640 --> 01:59.780 And so I'm going to start using these dots as my indicator that we have a layer 44 01:59.780 --> 02:00.280 three WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 44 01:59.780 --> 02:00.280 three 45 02:00.280 --> 02:01.520 interface. 46 02:01.520 --> 02:06.120 So if these are layer three connections, then I could put a dot where these 47 02:06.120 --> 02:07.280 lines intersect 48 02:07.280 --> 02:12.630 and this tells me that oh, these devices are all connected at layer three, 49 02:12.630 --> 02:13.140 which is very 50 02:13.140 --> 02:17.100 useful and very important when you're looking at a physical diagram and trying 51 02:17.100 --> 02:17.880 to tell what's 52 02:17.880 --> 02:19.740 going on. 53 02:19.740 --> 02:24.930 But the reality is that we might actually see layer three interfaces that aren 54 02:24.930 --> 02:25.860 't physical 55 02:25.860 --> 02:26.980 either. 56 02:26.980 --> 02:29.580 And so that creates an interesting situation. 57 02:29.580 --> 02:35.050 What if I have a couple of switches like this and it's more of a layer two top WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 57 02:29.580 --> 02:35.050 What if I have a couple of switches like this and it's more of a layer two top 58 02:35.050 --> 02:35.760 ology. 59 02:35.760 --> 02:39.600 So once again, I've got an ether channel between these two and then I've got a 60 02:39.600 --> 02:40.340 switch down 61 02:40.340 --> 02:43.700 here and I connect all these together. 62 02:43.700 --> 02:48.340 And so far, all of this is layer two and we know that because there's no dots. 63 02:48.340 --> 02:51.880 Now just to be abundantly clear, when I'm talking about these dots and layer 64 02:51.880 --> 02:52.740 three interfaces 65 02:52.740 --> 02:56.380 versus layer two, this is very much a Jeff thing. 66 02:56.380 --> 02:58.940 This is not an industry standard concept. 67 02:58.940 --> 03:02.090 So when you're looking at other people's diagrams, don't assume it's layer two WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 67 02:58.940 --> 03:02.090 So when you're looking at other people's diagrams, don't assume it's layer two 68 03:02.090 --> 03:02.520 because 69 03:02.520 --> 03:03.700 there's no dots. 70 03:03.700 --> 03:07.370 I'm teaching this from the perspective that as you dive into topologies, if you 71 03:07.370 --> 03:08.020 're drawing 72 03:08.020 --> 03:12.740 your own topologies, if you want to really be able to know what exactly you're 73 03:12.740 --> 03:13.380 drawing 74 03:13.380 --> 03:16.720 and look at it later and understand the topology or maybe you're doing a lab 75 03:16.720 --> 03:17.420 and you just want 76 03:17.420 --> 03:21.420 to draw it up real quick, this is a great way that you can do this. 77 03:21.420 --> 03:25.380 And so whether you choose to do it or not, it's perfectly up to you. 78 03:25.380 --> 03:29.300 But also understand that as I'm drawing things, that's how I'm representing 79 03:29.300 --> 03:30.220 information. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 79 03:29.300 --> 03:30.220 information. 80 03:30.220 --> 03:34.970 So as we're drawing this out, we might say, okay, this is all a layer two 81 03:34.970 --> 03:35.560 environment 82 03:35.560 --> 03:37.540 because there's no dots here. 83 03:37.540 --> 03:38.940 But where are the dots? 84 03:38.940 --> 03:41.780 Well, let's say that this is running a bunch of VLANs. 85 03:41.780 --> 03:47.060 Maybe I'm just running VLANs 10 and 20. 86 03:47.060 --> 03:50.870 And these are all trunk links, so I'm carrying the VLANs on all of these 87 03:50.870 --> 03:51.900 connections. 88 03:51.900 --> 03:54.620 Well VLANs 10 and 20 are going to need SVIs. 89 03:54.620 --> 03:58.600 They're going to need those switched virtual interfaces, which are VLAN 90 03:58.600 --> 03:59.500 interfaces. 91 03:59.500 --> 04:05.140 And so I can see these represented by dots here on the switches. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 91 03:59.500 --> 04:05.140 And so I can see these represented by dots here on the switches. 92 04:05.140 --> 04:09.260 And notice that they don't belong to any physical port, they're just sort of 93 04:09.260 --> 04:09.780 floating 94 04:09.780 --> 04:12.180 inside the switches. 95 04:12.180 --> 04:19.020 And so now I can see that I've got a VLAN 10, SVI, VLAN 20, SVI 10 and 20. 96 04:19.020 --> 04:24.780 And this shows me that there are layer three interfaces in the network. 97 04:24.780 --> 04:30.180 Furthermore, maybe I've got a router upstream and this router comes in from a WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 97 04:24.780 --> 04:30.180 Furthermore, maybe I've got a router upstream and this router comes in from a 98 04:30.180 --> 04:31.100 layer three 99 04:31.100 --> 04:34.870 perspective to these two switches and maybe we're running a routing protocol up 100 04:34.870 --> 04:35.260 to that 101 04:35.260 --> 04:36.260 router. 102 04:36.260 --> 04:41.140 And now we can start to see the layer three world coming together and also 103 04:41.140 --> 04:42.620 understand that 104 04:42.620 --> 04:46.400 while I might need to do layer two switching to go from one layer to interface 105 04:46.400 --> 04:46.980 to another 106 04:46.980 --> 04:51.810 layer to interface or something along those lines, if I'm routing out to maybe 107 04:51.810 --> 04:52.180 through 108 04:52.180 --> 04:57.580 a default gateway, now I see that this switch is able to route among these 109 04:57.580 --> 04:58.660 different layer 110 04:58.660 --> 05:00.460 three interfaces. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 110 04:58.660 --> 05:00.460 three interfaces. 111 05:00.460 --> 05:04.930 But also notice that an SVI is really no different from a physical interface, 112 05:04.930 --> 05:06.180 they're all treated 113 05:06.180 --> 05:09.500 the same from a layer three perspective. 114 05:09.500 --> 05:15.020 They just happen to be logical on the SVI side and physical on the port side. 115 05:15.020 --> 05:19.040 So now this is going to lead us to a different type of diagram because we've 116 05:19.040 --> 05:19.860 been focused 117 05:19.860 --> 05:25.020 on physical diagrams, but now we can start to draw those logical diagrams. 118 05:25.020 --> 05:29.700 We're starting to draw the logical diagrams or logical topologies. 119 05:29.700 --> 05:37.260 Now our focus is going to be on VLANs and subnets, but especially on VLANs WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 119 05:29.700 --> 05:37.260 Now our focus is going to be on VLANs and subnets, but especially on VLANs 120 05:37.260 --> 05:38.380 because they 121 05:38.380 --> 05:43.110 represent those layer two broadcast domains, which is how we really need to be 122 05:43.110 --> 05:43.780 thinking 123 05:43.780 --> 05:45.340 about VLANs. 124 05:45.340 --> 05:49.980 So what we can do now is say I want to draw this topology out, but do it 125 05:49.980 --> 05:51.100 logically. 126 05:51.100 --> 05:52.300 What do we have? 127 05:52.300 --> 05:58.320 Well, we have VLAN 10 interfaces, we have VLAN 20 interfaces, we've got a 128 05:58.320 --> 05:59.220 switch hanging 129 05:59.220 --> 06:02.100 off from a layer two perspective. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 129 05:59.220 --> 06:02.100 off from a layer two perspective. 130 06:02.100 --> 06:07.380 And so now what we can do is represent each one of those VLANs as one of these 131 06:07.380 --> 06:08.140 network 132 06:08.140 --> 06:09.140 segments. 133 06:09.140 --> 06:14.020 So here we have VLAN 10 and here we have VLAN 20. 134 06:14.020 --> 06:19.370 So VLAN 10 we see has, you know, through this other switch, maybe let's just 135 06:19.370 --> 06:20.020 add a couple 136 06:20.020 --> 06:21.260 of hosts on here. 137 06:21.260 --> 06:24.280 So now we've got a couple of hosts down here, one's on VLAN 10 and one's on V 138 06:24.280 --> 06:25.380 LAN 20. 139 06:25.380 --> 06:29.490 Now I can draw those hosts, which technically do have layer three interfaces, 140 06:29.490 --> 06:30.100 so we could WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 140 06:29.490 --> 06:30.100 so we could 141 06:30.100 --> 06:31.620 put a dot there if we wanted to. 142 06:31.620 --> 06:34.220 There's an IP address on that host. 143 06:34.220 --> 06:39.860 And so this host over here, the host in VLAN 20. 144 06:39.860 --> 06:41.940 Now how do they communicate to the rest of the world? 145 06:41.940 --> 06:43.860 Well, notice what we have on these switches. 146 06:43.860 --> 06:51.300 We have SVIs that are in VLAN 10 and VLAN 20. 147 06:51.300 --> 06:56.380 But also notice, as we count our dots here, that we're missing a few dots. 148 06:56.380 --> 07:01.860 For example, I've got two SVIs in VLAN 10. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 148 06:56.380 --> 07:01.860 For example, I've got two SVIs in VLAN 10. 149 07:01.860 --> 07:05.540 So this would be, we'll just call it switch one and switch two now. 150 07:05.540 --> 07:09.380 We didn't give them names, but we've got two different switches in that play 151 07:09.380 --> 07:09.860 here. 152 07:09.860 --> 07:12.100 So switch one and switch two. 153 07:13.100 --> 07:16.340 And so these both exist. 154 07:16.340 --> 07:17.980 I did that wrong. 155 07:17.980 --> 07:18.980 This should be a 10 here. 156 07:18.980 --> 07:19.980 There we go. 157 07:19.980 --> 07:21.900 So 10 and 10, 20 and 20. 158 07:21.900 --> 07:26.840 So now we see that all three of these layer three interfaces, whether we're 159 07:26.840 --> 07:27.580 talking about 160 07:27.580 --> 07:33.020 VLAN 10 or VLAN 20, they should be able to ping one another because they have WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 160 07:27.580 --> 07:33.020 VLAN 10 or VLAN 20, they should be able to ping one another because they have 161 07:33.020 --> 07:34.020 connectivity 162 07:34.020 --> 07:40.710 through this broadcast domain, through VLAN 10 on the left or VLAN 20 on the 163 07:40.710 --> 07:41.540 right. 164 07:41.540 --> 07:45.660 Now lastly, we can use sort of a blended approach, if we want to call it that. 165 07:45.660 --> 07:50.890 Again, this is not a really a standard term per se, but we could blend the 166 07:50.890 --> 07:51.740 world of layer, 167 07:51.740 --> 07:55.980 or a physical and logical together to see layer two networks. 168 07:55.980 --> 08:01.060 So in our situation here, maybe we draw switch one, the switch on the left. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 168 07:55.980 --> 08:01.060 So in our situation here, maybe we draw switch one, the switch on the left. 169 08:01.060 --> 08:05.440 And now instead of just drawing dots and downstream physical connections, we 170 08:05.440 --> 08:05.900 can still 171 08:05.900 --> 08:10.620 draw those dots to say, here's my VLAN interface for VLAN 10. 172 08:10.620 --> 08:18.890 But this is actually connected to a broadcast segment that switch two is also a 173 08:18.890 --> 08:19.220 part of. 174 08:19.220 --> 08:22.460 And with that other host as well. 175 08:22.460 --> 08:25.540 So this is again VLAN 10. 176 08:25.540 --> 08:29.030 And then maybe we'll use another color here just to distinguish, but I can also 177 08:29.030 --> 08:29.460 start to 178 08:29.460 --> 08:33.500 overlap a little bit with VLAN 20. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 178 08:29.460 --> 08:33.500 overlap a little bit with VLAN 20. 179 08:33.500 --> 08:35.740 And we'll see that we've got another VLAN. 180 08:35.740 --> 08:41.260 So VLAN 20 is at play here, and I connect these dots down. 181 08:41.260 --> 08:46.460 And then this connects to the host that's in VLAN 20. 182 08:46.460 --> 08:49.510 And so now we can start to really see the routing path that we need to take if 183 08:49.510 --> 08:49.780 these 184 08:49.780 --> 08:51.820 two hosts are to communicate. 185 08:51.820 --> 08:58.110 Because this host has no direct path to hop from the green VLAN 10 line to the 186 08:58.110 --> 08:58.780 orange 187 08:58.780 --> 09:02.180 or red VLAN 20 line, I can't do that. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 187 08:58.780 --> 09:02.180 or red VLAN 20 line, I can't do that. 188 09:02.180 --> 09:08.380 And what I need to do is I need to go through my default gateway here, this SVI 189 09:08.380 --> 09:09.380 get routed 190 09:09.380 --> 09:12.140 over to VLAN 20. 191 09:12.140 --> 09:18.150 And then that gets placed down into the layer two domain that gets passed to 192 09:18.150 --> 09:19.180 the host. 193 09:19.180 --> 09:21.180 Now does this show the physical path? 194 09:21.180 --> 09:23.180 Does it show this switch down here? 195 09:23.180 --> 09:24.700 No, it doesn't. 196 09:24.700 --> 09:29.350 All three of these types of diagrams are very useful, but they all contain some 197 09:29.350 --> 09:29.820 pieces 198 09:29.820 --> 09:32.780 of information without containing other pieces. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 198 09:29.820 --> 09:32.780 of information without containing other pieces. 199 09:32.780 --> 09:36.430 To see the full picture, we at least need a physical and logical, and sometimes 200 09:36.430 --> 09:36.740 we can 201 09:36.740 --> 09:39.660 blend those together as I've drawn out down here. 202 09:39.660 --> 09:43.740 And furthermore, once again, if we have additional routing paths, then we can 203 09:43.740 --> 09:44.820 see that as we 204 09:44.820 --> 09:50.530 connect up to whatever layer three domain sort of exists, northbound or beyond 205 09:50.530 --> 09:51.020 these 206 09:51.020 --> 09:52.020 two switches. 207 09:52.020 --> 09:58.150 But we could also see that I can route to my SVI and then route out this way to 208 09:58.150 --> 09:58.620 the rest 209 09:58.620 --> 10:01.920 of the network if I'm trying to say get out to the internet or something along WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 209 09:58.620 --> 10:01.920 of the network if I'm trying to say get out to the internet or something along 210 10:01.920 --> 10:03.380 those lines. 211 10:03.380 --> 10:08.740 But let's start thinking really truly about how layer two domains come together 212 10:08.740 --> 10:09.380 , how we 213 10:09.380 --> 10:14.090 can send layer two traffic, and how we can represent the layer three world with 214 10:14.090 --> 10:14.620 some of 215 10:14.620 --> 10:18.060 these dots to tell us where those interfaces really are.