WEBVTT 1 00:00.000 --> 00:04.300 Now, to ensure we're on the same exact sheet of music regarding why we would 2 00:04.300 --> 00:04.760 use something 3 00:04.760 --> 00:09.380 like OSPF to dynamically exchange routes, let's take a look at our existing top 4 00:09.380 --> 00:09.720 ology 5 00:09.720 --> 00:12.040 so far, which is right here. 6 00:12.040 --> 00:15.680 So in our previous skill, we connected the tier zero gateway and more 7 00:15.680 --> 00:16.680 specifically the 8 00:16.680 --> 00:20.800 services router function on the tier zero gateway to this network segment right 9 00:20.800 --> 00:21.280 here. 10 00:21.280 --> 00:24.400 And that's my 192.168.1 network. 11 00:24.400 --> 00:27.640 And we also verified the previous skill that we have basic connectivity from 12 00:27.640 --> 00:28.320 our tier zero 13 00:28.320 --> 00:33.760 gateway to this IP address right here of .1 on that 192.168.1 network. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 13 00:28.320 --> 00:33.760 gateway to this IP address right here of .1 on that 192.168.1 network. 14 00:33.760 --> 00:37.760 And just as a reminder here on this tier zero gateway, we are using edge one 15 00:37.760 --> 00:38.560 and also edge 16 00:38.560 --> 00:41.760 two and a logical interface of .62. 17 00:41.760 --> 00:46.920 And then we said a virtual IP address of .60 on this 192.168.1 network. 18 00:46.920 --> 00:49.690 So for any of those details regarding setting that up and getting that 19 00:49.690 --> 00:50.560 connectivity to this 20 00:50.560 --> 00:54.240 external segment right here, please feel free to check out that previous skill. 21 00:54.240 --> 00:57.600 And let's imagine for a moment that this computer right here, VM1 wants to 22 00:57.600 --> 00:58.480 communicate with 23 00:58.480 --> 01:00.000 a web server out on the internet. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 24 01:00.000 --> 01:03.520 Let's go ahead and choose a Google DNS server out at eight .8 .8 .8. 25 01:03.520 --> 01:07.200 Just as an example of a server in the treatable out on the internet. 26 01:07.200 --> 01:12.140 Now if this client has .1 on the 1010 zero network as its default gateway, it 27 01:12.140 --> 01:12.320 would 28 01:12.320 --> 01:17.190 forward the packet destined for 8888 to the layer two address of this interface 29 01:17.190 --> 01:17.760 here on 30 01:17.760 --> 01:18.920 gateway A. 31 01:18.920 --> 01:21.450 This gateway would look at the layer three destination address, make a 32 01:21.450 --> 01:22.280 forwarding decision 33 01:22.280 --> 01:26.720 to the next hop in the path, which would be the logical interface here on tier 34 01:26.720 --> 01:27.480 zero gateway 35 01:27.480 --> 01:28.480 zero. 36 01:28.480 --> 01:30.450 And then for the tier zero gateway, I'm going to just go ahead and shut out WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 36 01:28.480 --> 01:30.450 And then for the tier zero gateway, I'm going to just go ahead and shut out 37 01:30.450 --> 01:31.120 that we're doing 38 01:31.120 --> 01:35.490 the distributed router services there as well as these services router services 39 01:35.490 --> 01:35.720 for that 40 01:35.720 --> 01:39.360 external connectivity provided by our tier zero gateway zero. 41 01:39.360 --> 01:42.900 And then this router can forward that packet to the next hop at .1, assuming we 42 01:42.900 --> 01:43.320 have all 43 01:43.320 --> 01:44.320 the routes for that. 44 01:44.320 --> 01:47.690 And then this router would forward to the next hop and then to the next hop 45 01:47.690 --> 01:48.240 until finally 46 01:48.240 --> 01:50.400 is delivered over to 8888. 47 01:50.400 --> 01:53.810 Now for the return path, which I'll put in red here, it need be forward back to 48 01:53.810 --> 01:54.720 this router 49 01:54.720 --> 01:59.140 and then back to gateway zero and then down to gateway A and then down to the 50 01:59.140 --> 01:59.760 client for 51 01:59.760 --> 02:00.760 the return path. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 51 01:59.760 --> 02:00.760 the return path. 52 02:00.760 --> 02:04.170 So for that to work from an IP connectivity perspective, that presumes that we 53 02:04.170 --> 02:04.600 have all 54 02:04.600 --> 02:06.560 the correct routing in place. 55 02:06.560 --> 02:09.730 So this device, which will go ahead and label as physical router, would need to 56 02:09.730 --> 02:10.280 know that 57 02:10.280 --> 02:13.800 to reach the 1010 zero network, it needs to forward down this direction to the 58 02:13.800 --> 02:14.360 tier zero 59 02:14.360 --> 02:15.360 gateway. 60 02:15.360 --> 02:17.960 And then the tier zero gateway would forward down to gateway A who would then 61 02:17.960 --> 02:18.280 deliver it 62 02:18.280 --> 02:20.040 to VM one. 63 02:20.040 --> 02:24.300 So as far as default routes go, whenever we connect a tier one to a tier zero, 64 02:24.300 --> 02:25.320 automatically 65 02:25.320 --> 02:28.580 at that same time when we link this tier one to the tier zero, it doesn't like 66 02:28.580 --> 02:29.200 the injects 67 02:29.200 --> 02:32.350 a default route to this gateway says, Hey, if you don't know how to forward WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 67 02:29.200 --> 02:32.350 a default route to this gateway says, Hey, if you don't know how to forward 68 02:32.350 --> 02:32.800 anything 69 02:32.800 --> 02:36.040 more specifically in your routing table, just go ahead and forward it to the 70 02:36.040 --> 02:37.200 tier zero gateway. 71 02:37.200 --> 02:40.270 And the same thing for gateway B is going to have a default route to the tier 72 02:40.270 --> 02:41.280 zero gateway. 73 02:41.280 --> 02:44.680 Also in our previous skill, we set up a default route manually here on the 74 02:44.680 --> 02:46.160 gateway zero. 75 02:46.160 --> 02:48.520 We told it, Hey, if you don't have a better route and routing table, go ahead 76 02:48.520 --> 02:48.960 and forward 77 02:48.960 --> 02:51.000 it to dot one as your next top. 78 02:51.000 --> 02:52.560 So we manually set that up. 79 02:52.560 --> 02:57.540 However, what we did not walk through is the configuration of this router to 80 02:57.540 --> 02:58.240 train it on 81 02:58.240 --> 03:02.470 how to forward packets back to, for example, the 1010 zero network or the 1020 WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 81 02:58.240 --> 03:02.470 how to forward packets back to, for example, the 1010 zero network or the 1020 82 03:02.470 --> 03:03.440 zero network, 83 03:03.440 --> 03:06.600 because if we want packets coming back in from the internet to go back down to 84 03:06.600 --> 03:06.920 these 85 03:06.920 --> 03:10.690 clients and these VMs, this external router needs to know how to forward in the 86 03:10.690 --> 03:11.320 direction 87 03:11.320 --> 03:16.640 of 1010 zero or 1020 zero using our tier zero gateway address as it's next up. 88 03:16.640 --> 03:20.390 So our options for training our routed environments, whether they're NSX down 89 03:20.390 --> 03:21.360 here or physical 90 03:21.360 --> 03:24.940 environments up here, our options include setting up static routes and think of 91 03:24.940 --> 03:25.400 a static 92 03:25.400 --> 03:29.760 route like a specific configured instruction that you and I give to a router. 93 03:29.760 --> 03:33.310 We tell, for example, this physical router, hey, you need to get to 1010 zero WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 93 03:29.760 --> 03:33.310 We tell, for example, this physical router, hey, you need to get to 1010 zero 94 03:33.310 --> 03:33.840 anything 95 03:33.840 --> 03:37.680 forward it down here to this tier zero gateway address, which would be using 96 03:37.680 --> 03:38.440 dot 60. 97 03:38.440 --> 03:43.080 That's its virtual IP address for its interfaces connected to this segment or 98 03:43.080 --> 03:43.880 to get to the 99 03:43.880 --> 03:47.200 1020 zero network forward it to this gateway address. 100 03:47.200 --> 03:50.480 Again, that'd be the tier zero gateway address on that common segment. 101 03:50.480 --> 03:53.380 However, if we had another tier one router and we had another segment with 102 03:53.380 --> 03:54.640 another subnet, 103 03:54.640 --> 03:56.800 that also means we have to go back to this physical router. 104 03:56.800 --> 04:00.720 And once again, add a static route to reach that 10, for example, let's say it WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 104 03:56.800 --> 04:00.720 And once again, add a static route to reach that 10, for example, let's say it 105 04:00.720 --> 04:01.320 's 30 to 106 04:01.320 --> 04:02.880 reach that new network, let's say it's 1030. 107 04:02.880 --> 04:05.540 Again, that'd be another static route we have to add here. 108 04:05.540 --> 04:09.910 So another and more convenient option for training networking devices on how to 109 04:09.910 --> 04:10.440 forward 110 04:10.440 --> 04:14.040 IP packets is to use a dynamic routing protocol. 111 04:14.040 --> 04:16.280 So let me clear up a little bit of this. 112 04:16.280 --> 04:19.230 And with dynamic routing protocols, if we're in the same dynamic routing 113 04:19.230 --> 04:19.840 protocol, for 114 04:19.840 --> 04:25.330 example, here as well as here, that allows these two devices, these two layer 115 04:25.330 --> 04:26.240 three routers 116 04:26.240 --> 04:29.720 to dynamically share information regarding what's reachable. 117 04:29.720 --> 04:33.020 For example, this tier zero gateway could say, Hey, if you ever need to reach WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 117 04:29.720 --> 04:33.020 For example, this tier zero gateway could say, Hey, if you ever need to reach 118 04:33.020 --> 04:33.800 the 1010 119 04:33.800 --> 04:37.600 network, go ahead and forward packets to me for that subnet or vice versa. 120 04:37.600 --> 04:41.820 If we want this router right here to advertise a default route and say, Hey, if 121 04:41.820 --> 04:42.000 you ever 122 04:42.000 --> 04:44.710 need to get to anywhere and you don't have a more specific route in your router 123 04:44.710 --> 04:45.200 table, 124 04:45.200 --> 04:46.200 forward it to me. 125 04:46.200 --> 04:50.440 So we could advertise specific subnets and or default routes back and forth. 126 04:50.440 --> 04:54.240 And in the world of NSX, there's two options as we mentioned in the intro. 127 04:54.240 --> 04:57.360 One is border gateway protocol, which will cover any separate skill. 128 04:57.360 --> 05:01.900 And the other dynamic routing protocol is OSPF, which is an acronym for open WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 128 04:57.360 --> 05:01.900 And the other dynamic routing protocol is OSPF, which is an acronym for open 129 05:01.900 --> 05:02.560 shortest 130 05:02.560 --> 05:03.560 path first. 131 05:03.560 --> 05:07.560 So if we're running OSPF here and here, and we have both of them configured. 132 05:07.560 --> 05:12.040 Correctly, this router can dynamically learn how to reach the 1010 zero network 133 05:12.040 --> 05:12.240 and the 134 05:12.240 --> 05:13.240 1020 zero network. 135 05:13.240 --> 05:17.540 And our tier zero gateway can also learn about reachability to other networks 136 05:17.540 --> 05:17.800 that are being 137 05:17.800 --> 05:20.120 advertised from this physical router. 138 05:20.120 --> 05:23.400 So let's clean this up a little bit and talk about a few of the key components 139 05:23.400 --> 05:23.960 regarding 140 05:23.960 --> 05:27.720 this routing protocol called OSPF. 141 05:27.720 --> 05:29.840 Now with the OSPF, there's a few different flavors. 142 05:29.840 --> 05:34.240 There's OSPF version two, which is also just commonly called OSPF. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 142 05:29.840 --> 05:34.240 There's OSPF version two, which is also just commonly called OSPF. 143 05:34.240 --> 05:37.880 And that supports IP version four, and that's the flavor we're going to chat 144 05:37.880 --> 05:38.360 and talk 145 05:38.360 --> 05:39.920 about in this skill. 146 05:39.920 --> 05:43.320 So regarding OSPF, let's go ahead and put a few routers in place. 147 05:43.320 --> 05:48.960 I'll go ahead and put a few here and another set here and more down here. 148 05:48.960 --> 05:53.160 So in a large environment, it's very likely we're going to have dozens, if not 149 05:53.160 --> 05:53.720 more, logical 150 05:53.720 --> 05:54.720 layer three routers. 151 05:54.720 --> 05:57.200 And then we have our connectivity between those. 152 05:57.200 --> 05:59.920 However, they're connected physically or logically. 153 05:59.920 --> 06:02.080 And each of these lines represents an IP subnet. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 153 05:59.920 --> 06:02.080 And each of these lines represents an IP subnet. 154 06:02.080 --> 06:04.600 And let me go ahead and number these routers as well. 155 06:04.600 --> 06:07.800 And for Paul tolerance, let me also go ahead and put a segment right there too. 156 06:07.800 --> 06:09.680 And not every router needs to be connected to another router. 157 06:09.680 --> 06:13.740 So when we have some networks here, for example, VLANs that only have one 158 06:13.740 --> 06:14.720 router interface 159 06:14.720 --> 06:15.720 on them. 160 06:15.720 --> 06:18.560 So at the end of the day, each of these lines represents an IP subnet, 161 06:18.560 --> 06:19.540 including these down 162 06:19.540 --> 06:22.160 here and all these interconnections as well. 163 06:22.160 --> 06:25.080 And just for fun, let's also label a few of these subnets. 164 06:25.080 --> 06:33.880 We'll make this 10.8 and 10.9 and 10.10 and 10.11 and 10.12. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 164 06:25.080 --> 06:33.880 We'll make this 10.8 and 10.9 and 10.10 and 10.11 and 10.12. 165 06:33.880 --> 06:36.720 So we can add a couple more zeros and a slash 24. 166 06:36.720 --> 06:39.840 We'll call everything in this network topology a 24-bit network. 167 06:39.840 --> 06:43.840 So the question might be, how does router six know about how to forward down to 168 06:43.840 --> 06:44.120 the 169 06:44.120 --> 06:46.520 10.8 network or the 10.12 network? 170 06:46.520 --> 06:49.440 And the answer is if we're not going to use a dynamic routing protocol, we'd 171 06:49.440 --> 06:49.920 have to have 172 06:49.920 --> 06:53.400 static routes to say, hey, forward either to here or here or there. 173 06:53.400 --> 06:56.210 However, with the dynamic routing protocol, we can have all these routers share 174 06:56.210 --> 06:56.720 information 175 06:56.720 --> 06:57.720 with each other. 176 06:57.720 --> 07:01.840 So the language of love in the world of OSPF is called an LSA. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 176 06:57.720 --> 07:01.840 So the language of love in the world of OSPF is called an LSA. 177 07:01.840 --> 07:06.560 And when you see the term LSA, I'd like you to think of it like a puzzle piece. 178 07:06.560 --> 07:09.430 And although there are different types of LLCs that are used, the basic 179 07:09.430 --> 07:09.960 component of 180 07:09.960 --> 07:11.880 an LSA is information about the network. 181 07:11.880 --> 07:15.620 So this router right here, router six, is directly connected to this network, 182 07:15.620 --> 07:15.920 we'll 183 07:15.920 --> 07:21.010 have 10.56 and we'll call this one 10.67 and we'll call this network segment 184 07:21.010 --> 07:22.040 right here, 185 07:22.040 --> 07:23.040 10.106. 186 07:23.040 --> 07:26.420 So from the perspective of this router router six, it can send out link state 187 07:26.420 --> 07:27.280 advertisements 188 07:27.280 --> 07:32.090 or LSA's or puzzle pieces, if you will, to say, hey, I'm connected to these WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 188 07:27.280 --> 07:32.090 or LSA's or puzzle pieces, if you will, to say, hey, I'm connected to these 189 07:32.090 --> 07:32.960 three network 190 07:32.960 --> 07:37.480 segments, the 10.56, the 10.67 and the 10.106. 191 07:37.480 --> 07:41.220 Now not only is our six router six doing that and sending the information out, 192 07:41.220 --> 07:41.840 but every 193 07:41.840 --> 07:46.240 other router running OSPF is also sending out all the information it has about 194 07:46.240 --> 07:46.880 as directly 195 07:46.880 --> 07:48.240 connected networks. 196 07:48.240 --> 07:51.790 And although there's more than just one type of LSA for this discussion, I'd 197 07:51.790 --> 07:52.240 like you to 198 07:52.240 --> 07:56.110 imagine that it's link state advertisements from all the routers that are being 199 07:56.110 --> 07:56.960 advertised. 200 07:56.960 --> 07:59.880 And these link state advertisements are being flooded or forwarded throughout 201 07:59.880 --> 08:00.320 the entire WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 201 07:59.880 --> 08:00.320 the entire 202 08:00.320 --> 08:01.320 network. 203 08:01.320 --> 08:03.910 So at the end of the day, this router right here, router eight, is going to 204 08:03.910 --> 08:04.560 have received 205 08:04.560 --> 08:09.190 a link state advertisement or multiple link state advertisements from router 206 08:09.190 --> 08:09.960 six indicating 207 08:09.960 --> 08:11.200 these three networks. 208 08:11.200 --> 08:15.240 Now router eight is also receiving that same information from the perspective 209 08:15.240 --> 08:15.640 of router 210 08:15.640 --> 08:17.320 four, router two, and router one. 211 08:17.320 --> 08:21.040 So at the end of the day, if every router has all the puzzle pieces about all 212 08:21.040 --> 08:21.800 the directly 213 08:21.800 --> 08:26.020 connected networks, it can go ahead and then map out based on any target 214 08:26.020 --> 08:27.720 network, the best 215 08:27.720 --> 08:30.680 path to use to forward in that direction. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 215 08:27.720 --> 08:30.680 path to use to forward in that direction. 216 08:30.680 --> 08:32.680 And that's why it's called open shortest path first. 217 08:32.680 --> 08:36.960 It's going to use the best path based on his calculations, having all the 218 08:36.960 --> 08:38.000 information, 219 08:38.000 --> 08:39.000 having all the puzzle pieces. 220 08:39.000 --> 08:43.910 Now, one of the challenges with those PFS that if we have a say 50 or 60 or 100 221 08:43.910 --> 08:44.800 routers, 222 08:44.800 --> 08:49.530 that's a lot of LSA's that every single router has to look at and processing 223 08:49.530 --> 08:50.960 used to calculate. 224 08:50.960 --> 08:53.760 So in large environments, let me clean this up just a little bit. 225 08:53.760 --> 08:57.380 Instead of having all the routers participate and have to process all the LSA's 226 08:57.380 --> 08:57.840 from all 227 08:57.840 --> 09:01.210 the other routers, well, we can use, we can actually group these routers into WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 227 08:57.840 --> 09:01.210 the other routers, well, we can use, we can actually group these routers into 228 09:01.210 --> 09:01.640 what are 229 09:01.640 --> 09:03.480 known as OSPF areas. 230 09:03.480 --> 09:08.560 So let's go ahead and put these three routers in an area called area zero. 231 09:08.560 --> 09:14.960 And maybe we put these routers over here in an area called area one. 232 09:14.960 --> 09:20.430 And then these routers over here, we put in an area called area two labels of 233 09:20.430 --> 09:20.880 area 234 09:20.880 --> 09:22.400 to each one of those. 235 09:22.400 --> 09:27.240 And that way, only the routers in the same area have to listen to and process 236 09:27.240 --> 09:27.600 all the 237 09:27.600 --> 09:31.080 links they'd advertisements from the other routers in that same area. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 237 09:27.600 --> 09:31.080 links they'd advertisements from the other routers in that same area. 238 09:31.080 --> 09:35.690 So instead of having 12 routers worth of LSA's being advertised and propagated 239 09:35.690 --> 09:36.560 across every 240 09:36.560 --> 09:39.560 single router in the entire domain, now we reduced it. 241 09:39.560 --> 09:43.100 So we have these four routers here that only have to listen to and process each 242 09:43.100 --> 09:43.360 other's 243 09:43.360 --> 09:45.520 LSA's area two also over here. 244 09:45.520 --> 09:48.400 We have five routers that have to listen to and process each other's. 245 09:48.400 --> 09:50.720 And up here in this area, we only have three. 246 09:50.720 --> 09:54.190 So here for area zero, I'm going to redraw this just a little bit and I'm going 247 09:54.190 --> 09:54.640 to draw 248 09:54.640 --> 09:59.780 it like this because what really happens in the world of OSPF is that the 249 09:59.780 --> 10:01.040 actual network WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 249 09:59.780 --> 10:01.040 actual network 250 10:01.040 --> 10:05.520 interfaces are members of an area and not the entire router itself. 251 10:05.520 --> 10:10.360 So in this case, we have both interfaces on router one, included in area zero. 252 10:10.360 --> 10:14.080 This interface here on router two included in area zero and this one as well. 253 10:14.080 --> 10:16.320 And then they can share LSA's with each other. 254 10:16.320 --> 10:20.200 And then for area one, router two has a couple interfaces included in area one 255 10:20.200 --> 10:20.600 and our three 256 10:20.600 --> 10:23.880 over here has one interface included as part of area two. 257 10:23.880 --> 10:28.120 And that's important because we do need some connectivity between the areas. 258 10:28.120 --> 10:32.710 So in this case, our three would be the link, if you will, between area zero WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 258 10:28.120 --> 10:32.710 So in this case, our three would be the link, if you will, between area zero 259 10:32.710 --> 10:33.840 and area two. 260 10:33.840 --> 10:37.330 And they have a fancy term for this type of device which is connected to two 261 10:37.330 --> 10:37.880 areas and 262 10:37.880 --> 10:41.920 they call it an area border router. 263 10:41.920 --> 10:44.520 And that would also be the case over here with R2. 264 10:44.520 --> 10:47.480 It would also be an area border router or ABR. 265 10:47.480 --> 10:51.650 So even though if we have large environments with lots of routers, we can carve 266 10:51.650 --> 10:52.280 them up 267 10:52.280 --> 10:56.410 into multiple areas most of the time in smaller networks war in the case where 268 10:56.410 --> 10:56.960 we have for 269 10:56.960 --> 11:00.490 example, these three routers and we're connecting to one or two external WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 269 10:56.960 --> 11:00.490 example, these three routers and we're connecting to one or two external 270 11:00.490 --> 11:01.560 resources here or one 271 11:01.560 --> 11:04.520 or two external physical routers or firewalls. 272 11:04.520 --> 11:08.000 We probably could get away with just a single area for OSPF. 273 11:08.000 --> 11:11.700 And when we do that, we're going to be using area zero and area zero, which can 274 11:11.700 --> 11:12.200 be written 275 11:12.200 --> 11:15.730 as a zero, depending on the vendor or zero dot zero dot zero, zero, zero, zero, 276 11:15.730 --> 11:15.840 either 277 11:15.840 --> 11:16.840 way is great. 278 11:16.840 --> 11:19.320 That is also known as the backbone area. 279 11:19.320 --> 11:23.700 So unless there's dozens or more of routers that are running and participating 280 11:23.700 --> 11:24.200 in OSPF, 281 11:24.200 --> 11:28.120 it's very likely we're going to have one single area called area zero. 282 11:28.120 --> 11:31.390 And then when we configure our routers, we'll specify which interfaces are WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 282 11:28.120 --> 11:31.390 And then when we configure our routers, we'll specify which interfaces are 283 11:31.390 --> 11:32.800 going to participate 284 11:32.800 --> 11:34.000 in area zero. 285 11:34.000 --> 11:36.040 So in our topology, it looks something like this. 286 11:36.040 --> 11:40.520 We would go ahead and have the physical router or routers with their interfaces 287 11:40.520 --> 11:41.120 participating 288 11:41.120 --> 11:42.480 in area zero. 289 11:42.480 --> 11:45.560 And then our tier zero interfaces, which are connected to that same segment, we 290 11:45.560 --> 11:45.680 would 291 11:45.680 --> 11:50.020 enable them with OSPF as well, specify that they're in area zero and away we go 292 11:50.020 --> 11:50.200 . 293 11:50.200 --> 11:54.440 Also here, I included a representation of our edge nodes because anytime we're 294 11:54.440 --> 11:54.840 using 295 11:54.840 --> 11:58.600 services such as connectivity to the external network, like we're doing right 296 11:58.600 --> 11:59.320 here, we're 297 11:59.320 --> 12:02.320 actually using the services of one or more of our edge nodes. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 297 11:59.320 --> 12:02.320 actually using the services of one or more of our edge nodes. 298 12:02.320 --> 12:06.660 So edge one is providing the address of dot 61 and edge two is the address of 299 12:06.660 --> 12:07.360 dot 62 on 300 12:07.360 --> 12:08.360 this tier zero gateway. 301 12:08.360 --> 12:11.160 And then we also have a virtual address of dot 60. 302 12:11.160 --> 12:15.900 So in our case, what we really have is a very small grouping or number of 303 12:15.900 --> 12:16.760 routers that are 304 12:16.760 --> 12:18.040 going to be running OSPF. 305 12:18.040 --> 12:22.670 So very likely we'd just be using OSPF area zero as a single area OSPF 306 12:22.670 --> 12:24.040 implementation. 307 12:24.040 --> 12:28.410 And the benefit of that is we can share routes regarding the 10.10 zero network 308 12:28.410 --> 12:28.600 from our 309 12:28.600 --> 12:32.120 tier zero gateway to the physical router or to the physical device. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 309 12:28.600 --> 12:32.120 tier zero gateway to the physical router or to the physical device. 310 12:32.120 --> 12:35.280 It could be a firewall that's doing layer three routing either way is great. 311 12:35.280 --> 12:39.200 And we could also advertise reachability information to the 10 dot 20 network 312 12:39.200 --> 12:39.800 as well. 313 12:39.800 --> 12:43.230 And if the external router was configured for it, it could advertise to us a 314 12:43.230 --> 12:43.960 default route 315 12:43.960 --> 12:46.980 to say, Hey, here's how you get to everywhere else. 316 12:46.980 --> 12:49.640 If you don't have a more specific route in your routing table. 317 12:49.640 --> 12:52.820 So let me clean some of this up and let's talk about a few other really 318 12:52.820 --> 12:53.840 important aspects 319 12:53.840 --> 12:56.280 regarding open shortest path first. 320 12:56.280 --> 13:01.080 Let's imagine this represents this segment right there. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 320 12:56.280 --> 13:01.080 Let's imagine this represents this segment right there. 321 13:01.080 --> 13:06.760 And my network that's the 192 168 one network with a 24 bit mask. 322 13:06.760 --> 13:10.750 And in our previous skill, we set up basic connectivity to that network segment 323 13:10.750 --> 13:10.840 . 324 13:10.840 --> 13:13.960 So let's imagine this represents our tier zero gateway right here. 325 13:13.960 --> 13:16.960 I'll just call it tier zero, which is this guy right here. 326 13:16.960 --> 13:20.000 And behind the scenes, when we're doing that external connectivity, that tier 327 13:20.000 --> 13:20.560 zero gateway 328 13:20.560 --> 13:23.950 is going to be using the services router function for that bridge, if you will, 329 13:23.950 --> 13:25.280 from the NSX 330 13:25.280 --> 13:27.960 routed environment down here to that physical segment. 331 13:27.960 --> 13:30.360 And then I'll go ahead and draw this router up here as well. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 331 13:27.960 --> 13:30.360 And then I'll go ahead and draw this router up here as well. 332 13:30.360 --> 13:31.960 So there's our router connected. 333 13:31.960 --> 13:35.960 I'll draw the little icon that represents this is a router or has a layer three 334 13:35.960 --> 13:36.480 routing 335 13:36.480 --> 13:37.480 function. 336 13:37.480 --> 13:40.840 And just for grants, I'd like to add one other routing device up here. 337 13:40.840 --> 13:42.120 We'll connect it as well. 338 13:42.120 --> 13:44.720 So I'll draw the icons here for the routing function. 339 13:44.720 --> 13:47.760 And for IP addressing, let's imagine this one's at dot one. 340 13:47.760 --> 13:51.440 And let's imagine this router has the address of dot 136. 341 13:51.440 --> 13:56.000 And for this T zero gateway, it has the virtual IP address of dot 60. 342 13:56.000 --> 13:59.530 And behind the scenes that virtual IP address of dot 60 is being supported by 343 13:59.530 --> 14:00.040 this pair WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 343 13:59.530 --> 14:00.040 this pair 344 14:00.040 --> 14:04.730 of edge nodes, which is edge one at dot 61 edge to a dot 62, which we 345 14:04.730 --> 14:05.720 configured in 346 14:05.720 --> 14:06.720 a previous skill. 347 14:06.720 --> 14:10.820 And I know [garbled] network segment right here to the color that's here, which is 348 14:10.820 --> 14:11.440 white. 349 14:11.440 --> 14:13.400 So I'll go ahead and put that in right here. 350 14:13.400 --> 14:14.400 Fantastic. 351 14:14.400 --> 14:20.360 And there's our network segment and I'll label it as well 192 168 dot 1.0. 352 14:20.360 --> 14:23.600 There's our network segment with a 24 bit mask that we're using there. 353 14:23.600 --> 14:24.600 Fantastic. 354 14:24.600 --> 14:25.600 All right. 355 14:25.600 --> 14:30.040 So we configured all three of these devices to run OSPF in order to share WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 355 14:25.600 --> 14:30.040 So we configured all three of these devices to run OSPF in order to share 356 14:30.040 --> 14:30.960 information 357 14:30.960 --> 14:32.240 back and forth with each other. 358 14:32.240 --> 14:36.200 For example, about the networks down here being shared with the top router and 359 14:36.200 --> 14:36.680 the router 360 14:36.680 --> 14:39.840 up here sharing the default router other routing information. 361 14:39.840 --> 14:43.330 In order for that information to be shared, we have to have what's known as a 362 14:43.330 --> 14:44.560 full adjacency. 363 14:44.560 --> 14:48.940 Think of a full adjacency like being on really good terms with a neighbor where 364 14:48.940 --> 14:49.520 like you'll 365 14:49.520 --> 14:51.640 share anything and talk to that neighbor. 366 14:51.640 --> 14:52.640 It's all good. 367 14:52.640 --> 14:56.820 This is what we need in OSPF is a full adjacency in order to share routing 368 14:56.820 --> 14:57.840 information. 369 14:57.840 --> 15:00.990 And not only do we have a full adjacency, but it's also referred to as being a WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 369 14:57.840 --> 15:00.990 And not only do we have a full adjacency, but it's also referred to as being a 370 15:00.990 --> 15:01.280 fully 371 15:01.280 --> 15:02.840 adjacent neighbor. 372 15:02.840 --> 15:05.200 And now I have some good news and some bad news. 373 15:05.200 --> 15:10.140 The good news is is that on most appliances and most devices that run OSPF, if 374 15:10.140 --> 15:10.880 we use the 375 15:10.880 --> 15:16.080 defaults most of the time, all the parameters are going to agree. 376 15:16.080 --> 15:20.670 And as a result, they can become OSPF neighbors, establish a full adjacency and 377 15:20.670 --> 15:21.440 start sharing 378 15:21.440 --> 15:24.000 information, routing information with each other. 379 15:24.000 --> 15:27.390 However, oftentimes, especially when we're dealing with two different vendors 380 15:27.390 --> 15:27.920 that might 381 15:27.920 --> 15:32.090 have slightly different values, if one of those parameters is not correct and WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 381 15:27.920 --> 15:32.090 have slightly different values, if one of those parameters is not correct and 382 15:32.090 --> 15:32.560 doesn't 383 15:32.560 --> 15:36.060 agree with the other side, for example, this router has a setting of A and this 384 15:36.060 --> 15:36.480 one has 385 15:36.480 --> 15:40.640 a setting of B for some parameter in OSPF that could prevent them from getting 386 15:40.640 --> 15:41.360 into a full 387 15:41.360 --> 15:43.760 adjacency and becoming fully adjacent neighbors. 388 15:43.760 --> 15:47.450 So I have an acronym I'd like to share with you that can help you remember a 389 15:47.450 --> 15:48.040 few of the 390 15:48.040 --> 15:52.480 key things that have to be in agreement for two OSPF neighbors to become fully 391 15:52.480 --> 15:53.360 adjacent. 392 15:53.360 --> 15:54.360 And they are stamp. 393 15:54.360 --> 15:57.280 And I'm going to go ahead and put a little extra T there. 394 15:57.280 --> 15:59.120 Let me explain what these are. 395 15:59.120 --> 16:01.960 The S is for the same network. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 395 15:59.120 --> 16:01.960 The S is for the same network. 396 16:01.960 --> 16:05.240 If this router here, I'll go ahead and label this as R1 and we'll label this as 397 16:05.240 --> 16:05.760 T0, which 398 16:05.760 --> 16:06.760 it already is. 399 16:06.760 --> 16:11.120 So if R1 and T0 for their connections to this common network, if R1 believes it 400 16:11.120 --> 16:13.000 's the 192.168.2 401 16:13.000 --> 16:17.660 network and the T0 gateway believes it's the 192.168.4 network, that is going 402 16:17.660 --> 16:17.880 to 403 16:17.880 --> 16:21.000 cause them to not agree on what that common network segment is. 404 16:21.000 --> 16:23.800 And as a result, they won't become fully adjacent neighbors. 405 16:23.800 --> 16:28.800 So here I'll say same IP net for the same IP subnet, which means the same IP 406 16:28.800 --> 16:29.480 network 407 16:29.480 --> 16:30.480 or subnet. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 407 16:29.480 --> 16:30.480 or subnet. 408 16:30.480 --> 16:33.640 Another thing they have to agree on is the timers. 409 16:33.640 --> 16:37.840 So periodically with OSPF, we're going to be sending out little hello messages. 410 16:37.840 --> 16:41.010 So if this router router one thinks that it should send out hello messages 411 16:41.010 --> 16:42.360 every 11 seconds 412 16:42.360 --> 16:46.840 and our T0 gateway thinks it should send out hello messages every 12 seconds. 413 16:46.840 --> 16:49.720 If they don't agree on those timers, they won't become neighbors. 414 16:49.720 --> 16:52.640 So let me remove those and let's talk about the other T here. 415 16:52.640 --> 16:56.600 They also need to agree on the OSPF network type. 416 16:56.600 --> 17:01.470 So in OSPF, if we have ethernet, it's going to be using an OSPF network type of WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 416 16:56.600 --> 17:01.470 So in OSPF, if we have ethernet, it's going to be using an OSPF network type of 417 17:01.470 --> 17:02.360 broadcast. 418 17:02.360 --> 17:07.110 And the OSPF network type of broadcast, and I'll add net there for network type 419 17:07.110 --> 17:07.360 , simply 420 17:07.360 --> 17:12.400 means that we can see and find each other via multicast on this common ethernet 421 17:12.400 --> 17:13.240 segment. 422 17:13.240 --> 17:16.630 So by default, if we're configuring routers and they're connected to ethernet 423 17:16.630 --> 17:17.200 segments, 424 17:17.200 --> 17:19.600 the default network type is going to be broadcast. 425 17:19.600 --> 17:23.440 However, if it's different on one vendor versus another one, that could prevent 426 17:23.440 --> 17:23.560 them 427 17:23.560 --> 17:24.560 from becoming neighbors. 428 17:24.560 --> 17:26.800 All right, let me clean that up a little bit. 429 17:26.800 --> 17:29.440 And the next one down here is the area. 430 17:29.440 --> 17:34.240 So if our one on this interface here thought, oh, this is area one. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 430 17:29.440 --> 17:34.240 So if our one on this interface here thought, oh, this is area one. 431 17:34.240 --> 17:38.600 And over here on our T0 gateway, it thought that this interface was connected 432 17:38.600 --> 17:38.960 to area 433 17:38.960 --> 17:43.010 51 or area zero, if they don't match, that will prevent them from becoming 434 17:43.010 --> 17:43.720 neighbors. 435 17:43.720 --> 17:46.400 They have to agree on all of these properties. 436 17:46.400 --> 17:51.430 Another gotcha that often happens with multi layer switches is the MTU isn't 437 17:51.430 --> 17:52.320 the same. 438 17:52.320 --> 17:55.920 So here for the routed interface on each of these logical devices, here we have 439 17:55.920 --> 17:56.140 our 440 17:56.140 --> 17:57.520 tier zero gateway. 441 17:57.520 --> 17:59.880 And here we have our external router. 442 17:59.880 --> 18:04.960 If the MTU, the maximum transmission unit for IP routing is set to, for example WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 442 17:59.880 --> 18:04.960 If the MTU, the maximum transmission unit for IP routing is set to, for example 443 18:04.960 --> 18:06.120 , 1504 444 18:06.120 --> 18:11.480 here and it's set to 1506 here, that information is communicated back and forth 445 18:11.480 --> 18:12.760 in the low messages. 446 18:12.760 --> 18:15.630 So if it doesn't match up, if it's not the same, that could prevent them from 447 18:15.630 --> 18:16.040 becoming 448 18:16.040 --> 18:17.040 neighbors. 449 18:17.040 --> 18:19.920 So this MTU is just for the routed logical interface. 450 18:19.920 --> 18:24.120 It's not applicable to our logical layer two switching or distributed switches, 451 18:24.120 --> 18:24.440 which 452 18:24.440 --> 18:27.080 most likely we're going to be using jumble frames there anyway. 453 18:27.080 --> 18:30.980 But from an OSPF perspective, from the routed interfaces, they both have to WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 453 18:27.080 --> 18:30.980 But from an OSPF perspective, from the routed interfaces, they both have to 454 18:30.980 --> 18:31.600 agree on the 455 18:31.600 --> 18:33.920 same MTU if they want to become neighbors. 456 18:33.920 --> 18:35.520 So let me clean that up a little bit. 457 18:35.520 --> 18:37.720 And then the last one right here is authentication. 458 18:37.720 --> 18:40.440 And you might say Keith, it says P there. 459 18:40.440 --> 18:42.440 That's because they wanted the the mnemonic to work. 460 18:42.440 --> 18:46.640 So so the P actually is for password, but in OSPF, they refer to it as the 461 18:46.640 --> 18:47.320 method for 462 18:47.320 --> 18:48.320 authentication. 463 18:48.320 --> 18:52.100 So if we're using a certain type of password up here on our one, whether the 464 18:52.100 --> 18:52.760 type or the 465 18:52.760 --> 18:56.580 actual string of text is different than the one used down here on our T zero 466 18:56.580 --> 18:57.200 gateway, 467 18:57.200 --> 18:59.360 once again, that would prevent them from becoming neighbors. 468 18:59.360 --> 19:03.540 And again, this will be super useful when we're doing troubleshooting of why, WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 468 18:59.360 --> 19:03.540 And again, this will be super useful when we're doing troubleshooting of why, 469 19:03.540 --> 19:04.600 why is my NSX 470 19:04.600 --> 19:09.470 environment not setting up a full adjacent neighborhood with my external router 471 19:09.470 --> 19:09.600 ? 472 19:09.600 --> 19:12.720 Because at that point, we want to go through this list and see what's different 473 19:12.720 --> 19:13.080 on the 474 19:13.080 --> 19:14.080 two ends. 475 19:14.080 --> 19:15.280 All right, so I clean that up a little bit. 476 19:15.280 --> 19:19.000 And let me talk about one last concept here before we go to the next video for 477 19:19.000 --> 19:19.320 a game 478 19:19.320 --> 19:20.320 plan. 479 19:20.320 --> 19:23.660 And that last concept on a common network segment like this, ethernet segment 480 19:23.660 --> 19:24.040 here, we're 481 19:24.040 --> 19:28.560 getting a OSPF is that we are going to have a DR and I apologize that it's the 482 19:28.560 --> 19:29.320 same exact 483 19:29.320 --> 19:31.920 acronym as we have for a distributed router. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 483 19:29.320 --> 19:31.920 acronym as we have for a distributed router. 484 19:31.920 --> 19:35.610 But in the case of OSPF, I'll draw a line here, in the case of OSPF, a 485 19:35.610 --> 19:36.960 designated router, 486 19:36.960 --> 19:41.000 which is the DR in OSPF, has certain responsibilities on that network segment. 487 19:41.000 --> 19:45.240 And we only need one of them for the basic function regarding OSPF on that 488 19:45.240 --> 19:46.440 network segment. 489 19:46.440 --> 19:49.670 And for fault tolerance, we're also going to have what's called a backup 490 19:49.670 --> 19:50.920 designated router 491 19:50.920 --> 19:54.840 in case the primary or first designated router is no longer available. 492 19:54.840 --> 19:59.730 So we're going to have one DR on an ethernet segment and one backup designated 493 19:59.730 --> 20:00.400 router on WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 493 19:59.730 --> 20:00.400 router on 494 20:00.400 --> 20:02.000 that same ethernet segment. 495 20:02.000 --> 20:07.080 So let's imagine that this is the DR right here and this is the BDR. 496 20:07.080 --> 20:10.000 And let me use this color right here for full adjacency. 497 20:10.000 --> 20:13.160 So when we see this, we'll realize that means a full adjacency. 498 20:13.160 --> 20:17.120 So the DR and BDR are assuming everything's correct here are going to form a 499 20:17.120 --> 20:18.040 full adjacency 500 20:18.040 --> 20:20.860 with each other, meaning they can share routes back and forth and communicate 501 20:20.860 --> 20:22.080 with each other. 502 20:22.080 --> 20:23.080 That's great. 503 20:23.080 --> 20:27.770 And every other router other than the DR and BDR is also going to form a full 504 20:27.770 --> 20:28.800 adjacency, 505 20:28.800 --> 20:33.800 but they're going to form a full adjacency with the DR and also with the BDR. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 505 20:28.800 --> 20:33.800 but they're going to form a full adjacency with the DR and also with the BDR. 506 20:33.800 --> 20:37.000 And the benefit of having the full adjacency with both is because if the 507 20:37.000 --> 20:37.560 designated router 508 20:37.560 --> 20:41.510 goes away or has a problem, it's already got a connection to the BDR and can 509 20:41.510 --> 20:42.200 start using 510 20:42.200 --> 20:45.520 that BDR and its routing services as part of OSPF. 511 20:45.520 --> 20:49.480 However, what we don't need is we don't need a third designated router. 512 20:49.480 --> 20:54.850 So the third device on the network here is going to be called a DR other, 513 20:54.850 --> 20:55.600 meaning it's 514 20:55.600 --> 20:59.160 not a DR, it's not a BDR, but it's a DR other. 515 20:59.160 --> 21:02.480 And then just for grands, let's bring a fourth device to this topology. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 515 20:59.160 --> 21:02.480 And then just for grands, let's bring a fourth device to this topology. 516 21:02.480 --> 21:03.600 We'll put it right here. 517 21:03.600 --> 21:05.000 We'll call this R4. 518 21:05.000 --> 21:09.700 So it would also establish a full adjacency between it and the DR and the BDR 519 21:09.700 --> 21:10.320 as such. 520 21:10.320 --> 21:12.960 And this would also be a DR other. 521 21:12.960 --> 21:14.600 So here's the designated router. 522 21:14.600 --> 21:16.280 Here's the backup designated router. 523 21:16.280 --> 21:18.400 This is a DR other and this is a DR other. 524 21:18.400 --> 21:22.380 And then for the relationship between these two DR others, they are going to be 525 21:22.380 --> 21:22.960 in what's 526 21:22.960 --> 21:23.960 called a two-way state. 527 21:23.960 --> 21:28.090 And the short story there is that as two OSPF devices on the same network 528 21:28.090 --> 21:29.320 segment are discovering 529 21:29.320 --> 21:33.280 each other and then forming their formal adjacency, they're going to go through WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 529 21:29.320 --> 21:33.280 each other and then forming their formal adjacency, they're going to go through 530 21:33.280 --> 21:33.960 a whole bunch 531 21:33.960 --> 21:38.560 of states, including the init and the two-way state and something called X-star 532 21:38.560 --> 21:39.640 to an exchange. 533 21:39.640 --> 21:43.000 I'll just put an EX for that before they go into a full adjacency. 534 21:43.000 --> 21:46.680 However, these routers are not going to bother going through the full formal 535 21:46.680 --> 21:47.440 adjacency with 536 21:47.440 --> 21:51.310 each other because they already have adjacencies with the DR on the network 537 21:51.310 --> 21:52.040 segment and the 538 21:52.040 --> 21:53.560 BDR on the network segment. 539 21:53.560 --> 21:56.000 Well, they would go ahead and they would form all the way up to the two-way 540 21:56.000 --> 21:56.600 state and that's 541 21:56.600 --> 21:59.240 where they would park and say, you know what, we really don't need a full adjac 542 21:59.240 --> 21:59.680 ency here 543 21:59.680 --> 22:03.520 because we've got our full adjacencies with the DR and BDR respectively. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 543 21:59.680 --> 22:03.520 because we've got our full adjacencies with the DR and BDR respectively. 544 22:03.520 --> 22:09.280 So in this topology here, these two devices, T0 and R4, they both are DR others 545 22:09.280 --> 22:09.960 because 546 22:09.960 --> 22:12.280 there was already a DR and BDR present. 547 22:12.280 --> 22:17.290 However, in the world of NSX, our tier zero gateways do not want to take on the 548 22:17.290 --> 22:18.480 responsibility 549 22:18.480 --> 22:21.760 or the role of being the designated router for a segment. 550 22:21.760 --> 22:26.520 So they have their priority effectively set to zero for that DR/BDR function. 551 22:26.520 --> 22:30.330 And even if we only have one router like we do right here, it's going to be the WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 551 22:26.520 --> 22:30.330 And even if we only have one router like we do right here, it's going to be the 552 22:30.330 --> 22:30.840 DR, this 553 22:30.840 --> 22:34.210 tier zero gateway as it connects to that segment and then builds an OSPF 554 22:34.210 --> 22:35.160 neighborhood with 555 22:35.160 --> 22:38.560 the DR, it's not going to act as a BDR. 556 22:38.560 --> 22:41.930 It's going to stay in the state of a DR other and just maintain its full adjac 557 22:41.930 --> 22:42.800 ency with this 558 22:42.800 --> 22:43.800 DR. 559 22:43.800 --> 22:47.170 And then if another router shows up that's willing to take on a responsibility 560 22:47.170 --> 22:47.800 as a DR 561 22:47.800 --> 22:51.160 or BDR and it becomes the BDR, it's at this point. 562 22:51.160 --> 22:55.880 This T0 gateway is going to establish the second full adjacency to that BDR. 563 22:55.880 --> 22:58.640 But again, just for the heads up, when we're setting up OSPF and we're 564 22:58.640 --> 22:59.560 leveraging these 565 22:59.560 --> 23:03.230 edge nodes, the edge nodes that are providing this external connectivity WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 565 22:59.560 --> 23:03.230 edge nodes, the edge nodes that are providing this external connectivity 566 23:03.230 --> 23:04.080 function, they 567 23:04.080 --> 23:08.840 are not going to by default be a DR or BDR on this segment. 568 23:08.840 --> 23:11.870 So now that we've taken a look at some of the details regarding OSPF 569 23:11.870 --> 23:12.800 specifically for 570 23:12.800 --> 23:15.240 IPV4, that's OSPF version two. 571 23:15.240 --> 23:19.540 In the next video, let's take our existing topology and let's put a specific 572 23:19.540 --> 23:20.240 game plan 573 23:20.240 --> 23:24.840 in place for the implementation and verification of OSPF. 574 23:24.840 --> 23:26.880 So I'll see you in the next video in just a moment.