WEBVTT 1 00:00.000 --> 00:06.060 Let's turn our attention to the access layer. A lot of our focus with two 2 00:06.060 --> 00:10.500 tier and three tier models is on the core and distribution side of things, but 3 00:10.500 --> 00:10.740 the 4 00:10.740 --> 00:14.220 access layer needs some attention as well. And we didn't spend a little bit of 5 00:14.220 --> 00:18.860 time in the last skill talking about our different topologies. But now we want 6 00:18.860 --> 00:18.940 to 7 00:18.940 --> 00:24.420 talk about how exactly we connect our distribution switches down to our 8 00:24.420 --> 00:30.300 access switches. Because even though we can come up with topologies for within WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 8 00:24.420 --> 00:30.300 access switches. Because even though we can come up with topologies for within 9 00:30.300 --> 00:35.460 the access layer, this connection is kind of interesting. Now in a traditional 10 00:35.460 --> 00:41.050 network architecture, we are going to create these as layer two links. And if 11 00:41.050 --> 00:41.140 we 12 00:41.140 --> 00:45.300 just had a single layer to link, we'd lack redundancy, but it would be very 13 00:45.300 --> 00:50.700 clean and very easy to deploy. For better or worse, we know that our topologies 14 00:50.700 --> 00:56.100 are a lot more complex than that. For example, when we really draw this out, we 15 00:56.100 --> 01:00.260 have a pair of distribution switches connected at layer two, by the way. And WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 15 00:56.100 --> 01:00.260 have a pair of distribution switches connected at layer two, by the way. And 16 01:00.260 --> 01:06.060 then down here, we have an access closet with many switches. And potentially we 17 01:06.060 --> 01:10.620 use those technologies we talked about our chassies or our stacks, but either 18 01:10.620 --> 01:15.260 way, even if we do stack all these together, we know that we are deploying this 19 01:15.260 --> 01:19.220 with spanning tree protocol at play. We're going to have to block one of these 20 01:19.220 --> 01:26.020 links, ideally on a pervlan basis. And ultimately, we are creating a very large 21 01:26.020 --> 01:33.100 layer two domain. Now this has some amount of benefits. Because if I were to WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 21 01:26.020 --> 01:33.100 layer two domain. Now this has some amount of benefits. Because if I were to 22 01:33.100 --> 01:33.420 draw 23 01:33.420 --> 01:38.340 this out, going to another access closet, so this is closet number one, and 24 01:38.340 --> 01:38.460 this 25 01:38.460 --> 01:43.940 is closet number two. And we're going into another maybe a switchback here, or 26 01:43.940 --> 01:44.100 a 27 01:44.100 --> 01:47.540 set of switches. And yeah, we're going to block one of these links from a 28 01:47.540 --> 01:51.540 spanning tree perspective. But ultimately, what we have here is we have a 29 01:51.540 --> 01:58.620 extended layer two environment. So now I can have a host over here, a user that 30 01:58.620 --> 01:58.660 's 31 01:58.660 --> 02:04.420 connected in to the access closet on the right. And I can have an user over WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 31 01:58.660 --> 02:04.420 connected in to the access closet on the right. And I can have an user over 32 02:04.420 --> 02:04.780 here 33 02:04.780 --> 02:08.540 that's connected to the access closet on the left. And these can be part of the 34 02:08.540 --> 02:13.860 same VLAN and the same broadcast domain and the same subnet. So this user over 35 02:13.860 --> 02:23.500 here could be 10.100.1.5. And this device over here could be 10.100.1.7. And 36 02:23.500 --> 02:23.900 they 37 02:23.900 --> 02:30.580 can communicate at layer two. This gives us a maximum amount of flexibility. So WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 37 02:23.900 --> 02:30.580 can communicate at layer two. This gives us a maximum amount of flexibility. So 38 02:30.580 --> 02:36.620 we're talking about the pros, the benefits of this design. We have flexibility 39 02:36.620 --> 02:43.940 because I might need to deploy something who knows what over here, a device 40 02:43.940 --> 02:53.140 that needs to be on the same subnet as this device over here. If that's the 41 02:53.140 --> 02:57.740 case and that's what I need, then this design is going to support that. And I 42 02:57.740 --> 02:57.980 might 43 02:57.980 --> 03:03.220 not need this today, but I might need it in the future. And that's one of the WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 43 02:57.980 --> 03:03.220 not need this today, but I might need it in the future. And that's one of the 44 03:03.220 --> 03:07.740 concerns of this layer to design is just making sure again from a flexibility 45 03:07.740 --> 03:13.180 perspective that I can do whatever I need to do from a from a deployment 46 03:13.180 --> 03:17.020 perspective in the future, because I've built my network out with layer two. 47 03:17.020 --> 03:17.900 But 48 03:17.900 --> 03:25.860 here's the thing about this in the modern network. This need is less and less 49 03:25.860 --> 03:32.660 because most of my users are not trying to communicate with other devices on WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 49 03:25.860 --> 03:32.660 because most of my users are not trying to communicate with other devices on 50 03:32.660 --> 03:32.780 the 51 03:32.780 --> 03:38.200 local network. Rather, they're going out to my data center to communicate with 52 03:38.200 --> 03:38.340 my 53 03:38.340 --> 03:44.900 applications. Or increasingly more and more these days, I'm going out to the 54 03:44.900 --> 03:51.380 internet where I also have applications. Cloud applications, software, whatever 55 03:51.380 --> 03:51.580 it 56 03:51.580 --> 03:56.820 is that I'm connecting to. But this is more what we'd refer to as northbound 57 03:56.820 --> 04:00.460 traffic. If I look at my drawing over on the left, we call it northbound WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 57 03:56.820 --> 04:00.460 traffic. If I look at my drawing over on the left, we call it northbound 58 04:00.460 --> 04:00.860 traffic 59 04:00.860 --> 04:05.380 because I'm sending it through the distribution layer to whatever lies beyond 60 04:05.380 --> 04:09.500 that. Maybe it's a dedicated core, maybe it's a collapsed core, but I'm going 61 04:09.500 --> 04:09.740 out to 62 04:09.740 --> 04:14.980 the internet or to my data center. But regardless, it's northbound traffic. I'm 63 04:14.980 --> 04:19.980 not necessarily doing this east west traffic type of network flow anymore, 64 04:19.980 --> 04:26.820 going from one user to another or maybe a printer of some kind over here that 65 04:26.820 --> 04:31.980 used to require layer two communications and connectivity. It just doesn't WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 65 04:26.820 --> 04:31.980 used to require layer two communications and connectivity. It just doesn't 66 04:31.980 --> 04:32.700 happen 67 04:32.700 --> 04:38.060 as often in our modern networks. Another aspect of traditional network 68 04:38.060 --> 04:38.740 architectures 69 04:38.740 --> 04:43.980 where this was more required was wireless roaming because when I look at my 70 04:43.980 --> 04:49.420 wireless roaming, we'll say Wi-Fi roaming here. When I look at my wireless 71 04:49.420 --> 04:55.020 roaming, I always want to roam at layer two. If I perform a layer three 72 04:55.020 --> 04:59.700 roam, I have to change IP addresses and that gets extremely complex and usually 73 04:59.700 --> 05:04.700 results in dropped sessions. So I want to stay at layer two. And the reality is WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 73 04:59.700 --> 05:04.700 results in dropped sessions. So I want to stay at layer two. And the reality is 74 05:04.700 --> 05:10.340 that a wireless user here. So I guess this is an old cell phone with an antenna 75 05:10.340 --> 05:10.540 on 76 05:10.540 --> 05:15.960 it. I don't know. But either way, we have some kind of mobile device here. And 77 05:15.960 --> 05:16.620 we 78 05:16.620 --> 05:23.260 might start by communicating to an access point here connected to Closet 2 on 79 05:23.260 --> 05:29.300 the right. And I walk this way. And now I'm connected to an access point that's 80 05:29.300 --> 05:36.740 hanging off of Closet 1. So this transition, this wireless roam, will be at WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 80 05:29.300 --> 05:36.740 hanging off of Closet 1. So this transition, this wireless roam, will be at 81 05:36.740 --> 05:36.940 layer 82 05:36.940 --> 05:41.100 two these days, which is or with this design. And that's really good. We still 83 05:41.100 --> 05:46.340 want layer two roaming on the modern network. But in the modern network, 84 05:46.340 --> 05:54.700 wireless roaming is determined oftentimes by wireless controllers. And if we 85 05:54.700 --> 05:58.820 have wireless controllers in place in the network, the layer two happens 86 05:58.820 --> 06:03.220 regardless of what the underlying infrastructure looks like, thanks to our WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 86 05:58.820 --> 06:03.220 regardless of what the underlying infrastructure looks like, thanks to our 87 06:03.220 --> 06:10.220 tunneling mechanism. So the fact that we have tunnels means that we almost like 88 06:10.220 --> 06:14.380 that fabric concept where we're sending our layer two traffic over whatever 89 06:14.380 --> 06:18.380 the underlay is. And at that point, we're good to go. We are performing our 90 06:18.380 --> 06:18.820 roaming 91 06:18.820 --> 06:25.020 via layer two, even if the underlying architecture isn't layer two. And so yeah 92 06:25.020 --> 06:25.020 , 93 06:25.020 --> 06:31.220 we've got this flexible nature of layer two, but we do have to consider that we WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 93 06:25.020 --> 06:31.220 we've got this flexible nature of layer two, but we do have to consider that we 94 06:31.220 --> 06:36.540 don't necessarily need it in a lot of our environments. But at the same time, 95 06:36.540 --> 06:42.260 this is also a fairly simple architecture. And that's really good from a 96 06:42.260 --> 06:50.580 supportability perspective. So those are the benefits of a layer two access 97 06:50.580 --> 06:50.780 layer. 98 06:50.780 --> 06:56.420 But what are some of the downsides to this? Well, the biggest downside and it 99 06:56.420 --> 07:03.020 just is what it is. Anytime we have spanning tree at play, it is a downside. We WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 99 06:56.420 --> 07:03.020 just is what it is. Anytime we have spanning tree at play, it is a downside. We 100 07:03.020 --> 07:07.900 have to deal with spanning tree. This involves the potential for loops. And at 101 07:07.900 --> 07:07.940 a 102 07:07.940 --> 07:12.620 minimum, it involves us trying to manage our blocked ports. And that's going to 103 07:12.620 --> 07:16.380 require some amount of effort in order to properly block the right 104 07:16.380 --> 07:21.460 interfaces and make sure we're being efficient that way. For example, over here 105 07:21.460 --> 07:21.540 in 106 07:21.540 --> 07:25.820 our diagram, we're going to need to make, you know, maybe we make the the root 107 07:25.820 --> 07:26.100 of 108 07:26.100 --> 07:31.500 the network on the left here for some of our VLANs. And that would probably WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 108 07:26.100 --> 07:31.500 the network on the left here for some of our VLANs. And that would probably 109 07:31.500 --> 07:36.620 result in these links being blocked. But then we would want to create the root 110 07:36.620 --> 07:41.820 over here for other VLANs, which would block these links. It's a very common 111 07:41.820 --> 07:42.180 part 112 07:42.180 --> 07:48.140 of our network design to allow us to have multiple topologies so that our 113 07:48.140 --> 07:48.540 orange 114 07:48.540 --> 07:54.980 VLANs here can use this type of topology. We see it's loop free. But then our 115 07:54.980 --> 08:02.740 purple pink, whatever color this is, are this topology here. Also is loop free. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 115 07:54.980 --> 08:02.740 purple pink, whatever color this is, are this topology here. Also is loop free. 116 08:02.740 --> 08:07.260 And so half of VLANs go on this topology and half the VLANs go on the other top 117 08:07.260 --> 08:07.660 ology. 118 08:07.660 --> 08:12.620 But again, that requires extra configuration and complexity and makes it more 119 08:12.620 --> 08:17.260 difficult to troubleshoot issues when they happen. And so not only do we have 120 08:17.260 --> 08:21.940 to deal with spanning tree, but we have to worry about potentially broadcast 121 08:21.940 --> 08:30.100 storms or just flat out broadcast domains being large. So regardless of whether WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 121 08:21.940 --> 08:30.100 storms or just flat out broadcast domains being large. So regardless of whether 122 08:30.100 --> 08:36.140 a burst of traffic a storm is happening, regardless if we have dozens of 123 08:36.140 --> 08:41.020 access closets, we have more and more access closets here. The larger my layer 124 08:41.020 --> 08:45.100 to domain is going to be and the larger my layer to domain is the more I have 125 08:45.100 --> 08:45.260 to 126 08:45.260 --> 08:50.060 break it up into multiple subnets and still deal with broadcast traffic going 127 08:50.060 --> 08:50.220 to 128 08:50.220 --> 08:55.540 all of my closets where VLANs are enabled. It just can be very cumbersome to 129 08:55.540 --> 08:55.740 try to 130 08:55.740 --> 09:04.940 rein that in. So in the end, having this layer to access layer design is very WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 130 08:55.740 --> 09:04.940 rein that in. So in the end, having this layer to access layer design is very 131 09:04.940 --> 09:05.180 much 132 09:05.180 --> 09:09.260 how we traditionally do it. I would say even in the modern network, the vast 133 09:09.260 --> 09:14.460 majority of our organizations are deploying layer to access layer switches. But 134 09:14.460 --> 09:14.580 we 135 09:14.580 --> 09:18.180 do have to understand that while that does have some amount of benefits, some 136 09:18.180 --> 09:18.300 of 137 09:18.300 --> 09:21.940 those benefits just aren't as relevant anymore. And it does come with a bunch 138 09:21.940 --> 09:26.970 of downsides, which might lead us to want to talk about a different solution, 139 09:26.970 --> 09:27.060 which 140 09:27.060 --> 09:31.180 can lead us to either layer three access layer designs or even fabrics being WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 140 09:27.060 --> 09:31.180 can lead us to either layer three access layer designs or even fabrics being 141 09:31.180 --> 09:36.060 deployed that will change the way we extend our connectivity out to the access 142 09:36.060 --> 09:38.300 layer.