WEBVTT 1 00:00.000 --> 00:04.400 Before we jump into the lab and configure UDLD, it's important to know that 2 00:04.400 --> 00:09.000 there are two different modes of deploying this technology. 3 00:09.000 --> 00:14.830 The first of which is known as normal mode, and the second is known as 4 00:14.830 --> 00:17.000 aggressive mode. 5 00:17.000 --> 00:22.060 And generally speaking in production networks, we are going to use aggressive 6 00:22.060 --> 00:24.000 mode more often than not. 7 00:24.000 --> 00:26.000 So what's the difference? 8 00:26.000 --> 00:31.990 Well, when we configure UDLD on a link, we place the configuration on the WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 8 00:26.000 --> 00:31.990 Well, when we configure UDLD on a link, we place the configuration on the 9 00:31.990 --> 00:35.000 interface from one switch's perspective. 10 00:35.000 --> 00:38.600 And in order for UDLD to work, we're going to have to configure it on both 11 00:38.600 --> 00:40.000 sides as we might imagine. 12 00:40.000 --> 00:42.000 Because remember, we're using the echo concept. 13 00:42.000 --> 00:47.070 So if I send a keep alive to the other switch, if it doesn't know to loop it 14 00:47.070 --> 00:50.000 back around, then it's not going to be very useful to me. 15 00:50.000 --> 00:54.000 That doesn't just happen on its own. We need the UDLD running on both sides. 16 00:54.000 --> 00:58.850 But what's going to happen is that the UDLD keep alive is going to get sent out 17 00:58.850 --> 01:01.000 once every 15 seconds. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 17 00:58.850 --> 01:01.000 once every 15 seconds. 18 01:01.000 --> 01:04.000 And we're just making sure that that link stays up. 19 01:04.000 --> 01:09.710 Now, if for any reason we don't get anything back, the question is which mode 20 01:09.710 --> 01:13.000 are we running here as far as what our response is going to be. 21 01:13.000 --> 01:18.700 Normal mode is just going to basically send an informational log message to say 22 01:18.700 --> 01:21.000 , "Hey, something seems up on this link." 23 01:21.000 --> 01:25.000 It's going to place the port into what's known as an undetermined state. 24 01:25.000 --> 01:30.180 And effectively all we're really getting is a log message that says that again, WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 24 01:25.000 --> 01:30.180 And effectively all we're really getting is a log message that says that again, 25 01:30.180 --> 01:32.000 something appears to be wrong. 26 01:32.000 --> 01:36.560 That's why usually in production networks, we're going to want to run 27 01:36.560 --> 01:38.000 aggressive mode. 28 01:38.000 --> 01:44.980 Aggressive mode is going to wait for there to be a miss on some of these keep 29 01:44.980 --> 01:46.000 alive. 30 01:46.000 --> 01:50.190 And so once it is determined that the link has gone down, it's going to 31 01:50.190 --> 01:56.000 actually go into a second, let's call it another mini mode of operation here, 32 01:56.000 --> 02:00.000 where it's going to aggressively try to reform that connection. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 32 01:56.000 --> 02:00.000 where it's going to aggressively try to reform that connection. 33 02:00.000 --> 02:03.000 How exactly does it try to reform the connection? 34 02:03.000 --> 02:09.000 By sending eight keep alive in rapid succession, every second at this point. 35 02:09.000 --> 02:15.000 So we've missed some keep alive, we're saying, "Hey, maybe this link is down." 36 02:15.000 --> 02:19.300 We want to make sure that it is indeed down or it is indeed up one way or the 37 02:19.300 --> 02:20.000 other. 38 02:20.000 --> 02:23.610 Again, every 15 seconds doesn't tell us much. Let's go ahead and send a burst 39 02:23.610 --> 02:24.000 of messages. 40 02:24.000 --> 02:27.000 So we send eight of them every second. 41 02:27.000 --> 02:31.310 And if we don't get anything back at the end of that, we're going to then place WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 41 02:27.000 --> 02:31.310 And if we don't get anything back at the end of that, we're going to then place 42 02:31.310 --> 02:34.000 the port into air disable. 43 02:34.000 --> 02:38.490 As we mentioned, the goal of UDLD is to land an air disable to protect the 44 02:38.490 --> 02:40.000 network from loops. 45 02:40.000 --> 02:44.000 However, it's only aggressive mode that actually lands us in air disable. 46 02:44.000 --> 02:49.000 And so that's why typically we want to configure it for air disable. 47 02:49.000 --> 02:52.000 Now, there's a couple of things to consider with UDLD. 48 02:52.000 --> 02:56.000 First of all is the copper versus fiber conversation. 49 02:56.000 --> 03:00.000 As we might imagine, we're talking about unidirectional communications. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 49 02:56.000 --> 03:00.000 As we might imagine, we're talking about unidirectional communications. 50 03:00.000 --> 03:05.790 And the example we gave in the previous video of maybe fiber strands cracking 51 03:05.790 --> 03:08.000 or one of these types of situations, 52 03:08.000 --> 03:14.620 we probably would expect that fiber is going to have the most benefit from UDLD 53 03:14.620 --> 03:15.000 . 54 03:15.000 --> 03:19.600 After all, copper actually uses link pulses to determine whether or not all of 55 03:19.600 --> 03:21.000 the pairs are connected. 56 03:21.000 --> 03:25.000 However, we can deploy UDLD to both. 57 03:25.000 --> 03:30.000 Just as sort of a fail safe to our fail safes, if we really want to run it WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 57 03:25.000 --> 03:30.000 Just as sort of a fail safe to our fail safes, if we really want to run it 58 03:30.000 --> 03:32.000 across a copper connection, 59 03:32.000 --> 03:34.000 this goal will allow us to do so. 60 03:34.000 --> 03:38.000 Now, what's interesting about UDLD is how it's actually deployed. 61 03:38.000 --> 03:42.000 I mentioned that we want to deploy it to these individual interfaces. 62 03:42.000 --> 03:46.030 And so I can deploy it to an interface and I can deploy it to copper and fiber 63 03:46.030 --> 03:47.000 interfaces. 64 03:47.000 --> 03:51.000 But I can also configure it at a global level. 65 03:51.000 --> 03:56.590 And if I configure it at a global level, it's going to apply to all fiber ports 66 03:56.590 --> 03:57.000 . 67 03:57.000 --> 04:01.000 Yeah, it's not going to apply to copper ports if I enable it globally. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 67 03:57.000 --> 04:01.000 Yeah, it's not going to apply to copper ports if I enable it globally. 68 04:01.000 --> 04:05.400 So that's an important takeaway for us here, is for us to recognize if I wanted 69 04:05.400 --> 04:06.000 on copper ports, 70 04:06.000 --> 04:09.000 I have to manually deploy it to the interface. 71 04:09.000 --> 04:11.650 But if I just wanted on fiber, which is pretty typical, even in production 72 04:11.650 --> 04:12.000 networks, 73 04:12.000 --> 04:16.590 to say I'm going to focus on fiber, then I would deploy it globally to make 74 04:16.590 --> 04:20.000 sure that not only the fiber ports that are there today, 75 04:20.000 --> 04:25.000 but also fiber ports in the future will automatically run UDLD. 76 04:25.000 --> 04:30.210 Alright, let's go ahead and jump into the lab and in our lab, we've got a WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 76 04:25.000 --> 04:30.210 Alright, let's go ahead and jump into the lab and in our lab, we've got a 77 04:30.210 --> 04:32.000 similar topology to what we've used in the past, 78 04:32.000 --> 04:36.000 where we have a triangle of switches, we have switch three, 79 04:36.000 --> 04:39.220 and switch three happens to be the root. That's not going to come into play in 80 04:39.220 --> 04:41.000 this conversation, 81 04:41.000 --> 04:44.000 but it will when we look at loop guard. 82 04:44.000 --> 04:47.730 So one thing we may have noticed by the way in all of this is that UDLD is 83 04:47.730 --> 04:50.000 completely unrelated to spanning tree. 84 04:50.000 --> 04:56.000 Yes, it does block loops from forming by putting a port into air disable, 85 04:56.000 --> 04:59.000 but it doesn't actually tie into the STP process. 86 04:59.000 --> 05:02.320 It doesn't care where the root is, for example. It doesn't care about the flow WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 86 04:59.000 --> 05:02.320 It doesn't care where the root is, for example. It doesn't care about the flow 87 05:02.320 --> 05:03.000 of BP to use. 88 05:03.000 --> 05:07.490 Its job is simply to monitor a link and to shut it down if it goes into a unid 89 05:07.490 --> 05:09.000 irectional mode of operation. 90 05:09.000 --> 05:12.890 And so that's why it doesn't really matter as part of this video where the root 91 05:12.890 --> 05:13.000 is, 92 05:13.000 --> 05:16.000 but at the same time it might be helpful to know. 93 05:16.000 --> 05:21.310 And so we're going to apply UDLD here to switches three and five, that link 94 05:21.310 --> 05:22.000 between the two. 95 05:22.000 --> 05:27.670 And so that's going to be gig two slash one and gig two slash one on both 96 05:27.670 --> 05:29.000 switches. 97 05:29.000 --> 05:33.000 So let's go ahead and configure this on switch three. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 97 05:29.000 --> 05:33.000 So let's go ahead and configure this on switch three. 98 05:33.000 --> 05:37.750 I'm going to do a config T and from here I'll get on to interface gig two slash 99 05:37.750 --> 05:38.000 one. 100 05:38.000 --> 05:42.000 And then UDLD question mark, this is how we configure UDLD. 101 05:42.000 --> 05:45.630 I'm going to require the port command, but when I run question mark one more 102 05:45.630 --> 05:46.000 time, 103 05:46.000 --> 05:50.000 I'm going to find that I can either hit enter to enable normal mode, 104 05:50.000 --> 05:55.670 or I can type out aggressive here, and that's going to enable UDLD aggressive 105 05:55.670 --> 05:56.000 mode, 106 05:56.000 --> 05:58.000 which is again what we typically see. 107 05:58.000 --> 06:04.000 So when I go back out to my configuration prompt here, global exec, WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 107 05:58.000 --> 06:04.000 So when I go back out to my configuration prompt here, global exec, 108 06:04.000 --> 06:09.000 I can just do a show UDLD on an interface like gig two slash one. 109 06:09.000 --> 06:13.000 I can see a lot of information about how often messages are going out 110 06:13.000 --> 06:17.000 and whether we're in aggressive mode, for example, right there. 111 06:17.000 --> 06:19.000 So that's good information. 112 06:19.000 --> 06:25.000 And then also show UDLD neighbors will tell me who's out the other side. 113 06:25.000 --> 06:28.770 Now notice we haven't actually configured this on switch five yet, so we don't 114 06:28.770 --> 06:29.000 see anybody. 115 06:29.000 --> 06:33.980 And it's also important to know that at this point we've sent a bunch of WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 115 06:29.000 --> 06:33.980 And it's also important to know that at this point we've sent a bunch of 116 06:33.980 --> 06:34.000 messages 117 06:34.000 --> 06:37.000 and we haven't gotten anything echoed back. 118 06:37.000 --> 06:42.000 And if I do a show interface on gig two slash one, it's still in an up and up 119 06:42.000 --> 06:42.000 status. 120 06:42.000 --> 06:46.000 So why hasn't UDLD shut anything down yet? 121 06:46.000 --> 06:50.580 Well, fortunately Cisco recognized that if we want to deploy UDLD under a 122 06:50.580 --> 06:51.000 critical link, 123 06:51.000 --> 06:57.000 we didn't want to have to go so fast so as to make sure that UDLD doesn't shut 124 06:57.000 --> 06:57.000 a link 125 06:57.000 --> 07:00.020 down just because we configured it on one end, or maybe a misconfiguration WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 125 06:57.000 --> 07:00.020 down just because we configured it on one end, or maybe a misconfiguration 126 07:00.020 --> 07:02.000 would do that as well. 127 07:02.000 --> 07:07.530 Instead, switch three's UDLD process is going to wait to receive any other 128 07:07.530 --> 07:08.000 message 129 07:08.000 --> 07:11.000 from the other side before it will consider shutting it down. 130 07:11.000 --> 07:14.730 So yeah, it's sending keep-alives right now, and yes, it's not getting anything 131 07:14.730 --> 07:15.000 back, 132 07:15.000 --> 07:20.410 but until we configure UDLD on the other side, switch three is not going to 133 07:20.410 --> 07:21.000 think that 134 07:21.000 --> 07:24.570 there's a need to shut the port down because it hasn't received a keep-alive of 135 07:24.570 --> 07:25.000 its own. 136 07:25.000 --> 07:28.000 So now I'll go to switch five. 137 07:28.000 --> 07:34.000 Let's say config T, interface gig two slash one, and then I can do UDLD port WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 137 07:28.000 --> 07:34.000 Let's say config T, interface gig two slash one, and then I can do UDLD port 138 07:34.000 --> 07:37.000 aggressive. 139 07:37.000 --> 07:41.000 And at this point, let's just go back to switch three and run some of those 140 07:41.000 --> 07:41.000 same commands. 141 07:41.000 --> 07:46.320 So we did a show UDLD on this interface gig two slash one, and now we look at 142 07:46.320 --> 07:47.000 this. 143 07:47.000 --> 07:51.000 We actually see an entry listed here for the neighbor. 144 07:51.000 --> 07:54.000 We're in a current bidirectional state, which is good. 145 07:54.000 --> 07:57.000 We're sending messages every 15 seconds, also good. 146 07:57.000 --> 08:03.360 And then when I do a show UDLD neighbor, we also see the device on the other WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 146 07:57.000 --> 08:03.360 And then when I do a show UDLD neighbor, we also see the device on the other 147 08:03.360 --> 08:04.000 side. 148 08:04.000 --> 08:08.130 So these are very useful commands to validate that UDLD is working like we 149 08:08.130 --> 08:09.000 think it is. 150 08:09.000 --> 08:14.000 And again, we have to just configure this on an interface rather than globally. 151 08:14.000 --> 08:17.000 So in our lab environment, this is all virtual. 152 08:17.000 --> 08:18.000 There's no virtual fiber links. 153 08:18.000 --> 08:20.000 It's all virtual copper links. 154 08:20.000 --> 08:22.000 So we had to do it on the interface. 155 08:22.000 --> 08:26.060 And I wanted to configure it globally in a production real physical type of 156 08:26.060 --> 08:27.000 environment. 157 08:27.000 --> 08:31.000 I can do a config T and then UDLD question mark shows me my options. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 157 08:27.000 --> 08:31.000 I can do a config T and then UDLD question mark shows me my options. 158 08:31.000 --> 08:35.000 I can change the well, first of all, I can set aggressive mode. 159 08:35.000 --> 08:38.000 Interestingly, I'd say, oh, this should be UDLD port. 160 08:38.000 --> 08:43.000 Now it's UDLD enabled in order to configure it in normal mode. 161 08:43.000 --> 08:47.150 And then also I can change message time, like the amount of time that I send my 162 08:47.150 --> 08:48.000 messages. 163 08:48.000 --> 08:53.000 So I could just say UDLD aggressive here. 164 08:53.000 --> 08:56.000 And then it will automatically enable that on fiber ports. 165 08:56.000 --> 08:59.610 And actually it says that enable UDLD protocol in aggressive mode on fiber 166 08:59.610 --> 09:02.000 ports except where locally configured. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 166 08:59.610 --> 09:02.000 ports except where locally configured. 167 09:02.000 --> 09:06.640 So local configuration will always override global configuration, but do notice 168 09:06.640 --> 09:10.000 that this will only go to fiber ports when we configure it globally.