WEBVTT 0:00:03.300000 --> 0:00:05.940000 Hello and welcome to this video in which we're going to be doing just 0:00:05.940000 --> 0:00:12.240000 a quick review and refresher of how to map the topology with CDP and LLDP. 0:00:12.240000 --> 0:00:16.520000 Now don't have any formal lab tasks for this but it's just real easy using 0:00:16.520000 --> 0:00:19.860000 our topology just login devices and issue the commands you're going to 0:00:19.860000 --> 0:00:26.500000 see here just to look around and verify that CDP and LLDP are indeed working. 0:00:26.500000 --> 0:00:28.880000 So let's start with CDP. 0:00:28.880000 --> 0:00:31.020000 Stands for the Cisco Discovery Protocol. 0:00:31.020000 --> 0:00:35.560000 It is Cisco proprietary and it's used to map the network. 0:00:35.560000 --> 0:00:39.720000 So in ideal scenario, you would always have a network topology diagram 0:00:39.720000 --> 0:00:44.360000 in front of you that you could use that accurately displayed all the connections 0:00:44.360000 --> 0:00:45.840000 of every device. 0:00:45.840000 --> 0:00:49.820000 In reality, that's not always the case or sometimes you might be given 0:00:49.820000 --> 0:00:53.600000 something like that but it might be out of date or things might be missing 0:00:53.600000 --> 0:00:55.920000 just due to negligence or error. 0:00:55.920000 --> 0:01:00.220000 And so you might not even trust the topology diagram that you were given. 0:01:00.220000 --> 0:01:05.160000 Now, if you have all Cisco devices, if you have an entire Cisco network, 0:01:05.160000 --> 0:01:08.180000 then you can use actually the Cisco Discovery Protocol to dynamically 0:01:08.180000 --> 0:01:13.660000 determine what devices are directly connected to your Cisco router or 0:01:13.660000 --> 0:01:18.240000 switch and then branch out from there and actually draw a map yourself. 0:01:18.240000 --> 0:01:22.160000 So it provides layer two protocol discovery for neighbors. 0:01:22.160000 --> 0:01:27.260000 So CDP is not used to populate routing tables or forwarding tables of 0:01:27.260000 --> 0:01:32.280000 any way. It's purely an informational protocol and that's it. 0:01:32.280000 --> 0:01:37.580000 So when CDP messages are exchanged between a couple of Cisco devices and 0:01:37.580000 --> 0:01:42.960000 not all Cisco devices support CDP, but the ones that do will provide information 0:01:42.960000 --> 0:01:46.980000 about themselves like what type of device they are, what version of software 0:01:46.980000 --> 0:01:50.940000 they're running, what interface actually transmitted that information 0:01:50.940000 --> 0:01:58.520000 to you. So the main goal of CDP is to help with preparing a network diagram. 0:01:58.520000 --> 0:02:03.680000 Now in a lot of platforms, CDP is already enabled by default. 0:02:03.680000 --> 0:02:08.100000 Now, if you suspect it's not running, you can just type CDP run like we 0:02:08.100000 --> 0:02:10.740000 see right here and that will turn it on globally. 0:02:10.740000 --> 0:02:14.300000 If you're not sure, just type the command show CDP. 0:02:14.300000 --> 0:02:19.780000 As an example, I'm going to get into one of my devices here and I'm not 0:02:19.780000 --> 0:02:25.220000 sure if it's running CDP, it should be, but you know, we'll just verify. 0:02:25.220000 --> 0:02:32.120000 Let's just get into how about switch one. 0:02:32.120000 --> 0:02:43.320000 Okay, quick and easy way to determine if CDP is running, show CDP. 0:02:43.320000 --> 0:02:45.420000 And it says it is actually running. 0:02:45.420000 --> 0:02:48.220000 It is sending CDP packets every minute. 0:02:48.220000 --> 0:02:51.980000 That's the default hello interval for CDP every minute. 0:02:51.980000 --> 0:02:58.540000 It's sending a hold time of 180 seconds, which means that if I send a 0:02:58.540000 --> 0:03:02.720000 CDP message to you, giving you information about myself, you're going 0:03:02.720000 --> 0:03:05.140000 to hold on. So let's say I stop at that point. 0:03:05.140000 --> 0:03:07.800000 Now I should be doing that every minute. 0:03:07.800000 --> 0:03:11.960000 But let's say the first 60 seconds goes by and you haven't heard from 0:03:11.960000 --> 0:03:14.860000 me. Well, you're still going to cache that information. 0:03:14.860000 --> 0:03:18.160000 The next 60 seconds, so now 120 seconds goes by. 0:03:18.160000 --> 0:03:19.640000 You still haven't heard from me. 0:03:19.640000 --> 0:03:23.540000 You're going to cache that information only after three minutes or 180 0:03:23.540000 --> 0:03:24.680000 seconds has expired. 0:03:24.680000 --> 0:03:29.700000 If you haven't heard from me again, and all that time, then you'll age 0:03:29.700000 --> 0:03:33.460000 out the CDP information that you learned from me. 0:03:33.460000 --> 0:03:35.540000 So yes, CDP is running in this case. 0:03:35.540000 --> 0:03:36.500000 So that is good. 0:03:36.500000 --> 0:03:38.540000 We have confirmed that. 0:03:38.540000 --> 0:03:40.680000 You can change the CDP timer. 0:03:40.680000 --> 0:03:49.760000 Maybe you want CDP to reflect changes to host names of devices, changes 0:03:49.760000 --> 0:03:53.680000 of IP addresses, because CDP will actually tell you, hey, here's the IP 0:03:53.680000 --> 0:03:55.840000 addresses I have on myself. 0:03:55.840000 --> 0:04:01.240000 So the things that CDP can convey, if those types of things change, maybe 0:04:01.240000 --> 0:04:05.620000 you don't want to wait 60 seconds to propagate your next CDP message to 0:04:05.620000 --> 0:04:07.000000 reflect that change. 0:04:07.000000 --> 0:04:11.940000 So you could use the CDP timer command to influence your CDP Hello packets. 0:04:11.940000 --> 0:04:15.240000 I believe you can set those all the way down to 10 seconds if I'm not 0:04:15.240000 --> 0:04:18.560000 mistaken. Let's see. 0:04:18.560000 --> 0:04:24.920000 Five seconds in this particular, I have seen some platforms where 10 seconds 0:04:24.920000 --> 0:04:27.400000 was the lowest in this particular platform. 0:04:27.400000 --> 0:04:30.240000 You can reduce it all the way down to five seconds. 0:04:30.240000 --> 0:04:36.340000 Now you'll never be tested as far as what's the minimum and maximum configurable 0:04:36.340000 --> 0:04:41.780000 intervals for CDP, but you should know that this command CDP timer is 0:04:41.780000 --> 0:04:45.580000 the way you change the CDP Hello time. 0:04:45.580000 --> 0:04:50.840000 You could also disable CDP. 0:04:50.840000 --> 0:04:55.260000 You can either disable it globally with the no CDP run, or you could go 0:04:55.260000 --> 0:05:01.740000 to a particular interface and disable it there. 0:05:01.740000 --> 0:05:06.340000 And here are our commands for confirming CDP. 0:05:06.340000 --> 0:05:18.260000 So for example, show CDP neighbor is usually your starting point. 0:05:18.260000 --> 0:05:21.140000 It'll show you the various neighbors you've learned. 0:05:21.140000 --> 0:05:25.720000 It defaults to the host names of those devices, local interfaces, the 0:05:25.720000 --> 0:05:30.000000 interface on you that received this CDP packet. 0:05:30.000000 --> 0:05:36.460000 Port ID here is the interface on the other guy that sent you this information. 0:05:36.460000 --> 0:05:51.680000 Let's do another one that will show a little bit of difference here. 0:05:51.680000 --> 0:05:57.000000 All right. So for example, look at this third line right here. 0:05:57.000000 --> 0:06:03.120000 So we're on switch to, he received a CDP packet from switch three, switch 0:06:03.120000 --> 0:06:07.920000 to received it on his local interface of gig one slash two, but switch 0:06:07.920000 --> 0:06:12.960000 three sent it from his interface, a gig two slash zero. 0:06:12.960000 --> 0:06:16.280000 So that would be very critical information to know when drawing a network 0:06:16.280000 --> 0:06:17.780000 to polish diagram. 0:06:17.780000 --> 0:06:24.040000 You can get more information show CDP neighbor detail. 0:06:24.040000 --> 0:06:28.280000 See a lot more information about the capabilities of the device. 0:06:28.280000 --> 0:06:34.420000 You can see the software that device is running, the native VLAN of that 0:06:34.420000 --> 0:06:38.120000 device, all sorts of good information there. 0:06:38.120000 --> 0:06:44.880000 Now the thing about CDP is that as I mentioned, it's only Cisco proprietary. 0:06:44.880000 --> 0:06:48.500000 What if you want the same capabilities, the same ability to dynamically 0:06:48.500000 --> 0:06:52.600000 determine what's next to you and build a topology diagram using something 0:06:52.600000 --> 0:06:57.840000 other than CDP. Fortunately for you, there is something the IEEE came 0:06:57.840000 --> 0:07:02.920000 out with, which is called the link layer discovery protocol LLDP is the 0:07:02.920000 --> 0:07:08.960000 open standard equivalent to CDP defined as IEEE 802.1 AB. 0:07:08.960000 --> 0:07:10.800000 You'll never have to memorize that. 0:07:10.800000 --> 0:07:12.420000 Don't worry about that. 0:07:12.420000 --> 0:07:18.440000 One other nice thing about LLDP this has this optional thing called media 0:07:18.440000 --> 0:07:24.060000 endpoint discovery, which is where LLDP with Med can be used to dynamically 0:07:24.060000 --> 0:07:28.880000 discover IP phones and exchange information with that IP phone and have 0:07:28.880000 --> 0:07:33.160000 the IP phone tell your connected switch port information about itself. 0:07:33.160000 --> 0:07:39.260000 Now the only downside, not a huge downside these days, but the only downside 0:07:39.260000 --> 0:07:44.280000 to LLDP is that it only works basically over ethernet interfaces. 0:07:44.280000 --> 0:07:47.300000 So if you have an older Cisco router that's got like serial interfaces, 0:07:47.300000 --> 0:07:55.580000 for example, CDP will run over those serial interfaces, LLDP will not. 0:07:55.580000 --> 0:07:59.240000 And because they are completely separate independent protocols that do 0:07:59.240000 --> 0:08:06.120000 not talk to each other, CDP and LLDP can be operational on the same interface. 0:08:06.120000 --> 0:08:12.920000 So here's how you configure it, enable globally LLDP run. 0:08:12.920000 --> 0:08:16.180000 Here's how you set the whole time and the hello interval. 0:08:16.180000 --> 0:08:23.980000 And here's how you can turn it on on a particular interface. 0:08:23.980000 --> 0:08:29.040000 And viewing LLDP is as simple as typing show LLDP traffic. 0:08:29.040000 --> 0:08:33.600000 If you do that command every minute or so, you should see the entries 0:08:33.600000 --> 0:08:39.240000 increasing those values increasing, which proves that LLDP is being exchanged. 0:08:39.240000 --> 0:08:43.060000 And you can also do show LLDP neighbors and get basically the same type 0:08:43.060000 --> 0:08:46.180000 of information you got with show CDP neighbors. 0:08:46.180000 --> 0:08:52.840000 So that's it on this brief refresher and review of CDP and LLDP.