WEBVTT 0:00:07.160000 --> 0:00:11.780000 This video is titled, Common Problems at Layer 1 and Layer 2 and falls 0:00:11.780000 --> 0:00:17.200000 into Section 3 of the Cisco Certified Technician for Routing and Switching 0:00:17.200000 --> 0:00:22.640000 Curriculum. My name is Keith Bogart and I will be your instructor for 0:00:22.640000 --> 0:00:26.420000 this session. In this video, the main bullet point out of the blueprint 0:00:26.420000 --> 0:00:30.760000 that we are going to talk about is identifying and correcting problems 0:00:30.760000 --> 0:00:34.020000 at Layer 1 and Layer 2. 0:00:34.020000 --> 0:00:36.380000 So, let's go ahead and get right into that. 0:00:36.380000 --> 0:00:40.400000 So, before we jump into it, there is a troubleshooting progression. 0:00:40.400000 --> 0:00:43.700000 Basically, a series of two or three questions we have to ask ourselves 0:00:43.700000 --> 0:00:48.920000 in order to identify where do we start, on what device do we start our 0:00:48.920000 --> 0:00:49.920000 troubleshooting. 0:00:49.920000 --> 0:00:53.200000 So the first question you have to get an answer to is, is the problem 0:00:53.200000 --> 0:00:57.220000 reported by only a single person or by a group of people? 0:00:57.220000 --> 0:01:01.360000 If you have a whole bunch of people in a company or an office who are 0:01:01.360000 --> 0:01:05.720000 complaining of a lack of network connectivity, or maybe they have network 0:01:05.720000 --> 0:01:09.020000 connectivity but they just can't get to a certain website or a certain 0:01:09.020000 --> 0:01:14.120000 file server, then you know the problem is not on their laptops. 0:01:14.120000 --> 0:01:17.580000 You don't have to start at the laptop or PC level. 0:01:17.580000 --> 0:01:20.660000 Clearly, that's something in the network itself. 0:01:20.660000 --> 0:01:24.620000 So you would start by troubleshooting probably at either the switch that 0:01:24.620000 --> 0:01:27.940000 they're all connected to or the default gateway that they're all connected 0:01:27.940000 --> 0:01:31.260000 to, but you wouldn't have to start at the host level. 0:01:31.260000 --> 0:01:35.540000 Now, if it is a single person, if it's only one person who's complaining 0:01:35.540000 --> 0:01:39.300000 of the problem, you can simply say, you're fired and then get rid of that 0:01:39.300000 --> 0:01:40.820000 person and no more problem. 0:01:40.820000 --> 0:01:42.500000 Well, it's probably not that easy. 0:01:42.500000 --> 0:01:46.180000 But if it is a single person, is it only affecting a single destination 0:01:46.180000 --> 0:01:51.200000 or application? Or is it affecting all network access by that person? 0:01:51.200000 --> 0:01:57.040000 Once again, if someone says, hey, Keith, I can do web browsing, but my 0:01:57.040000 --> 0:01:59.340000 instant messaging is not working. 0:01:59.340000 --> 0:02:03.940000 Or I can't do any web browsing, but my email is working. 0:02:03.940000 --> 0:02:06.940000 Well, then in that case, because remember, we're focusing in this session 0:02:06.940000 --> 0:02:11.540000 on layer one and layer two problems, it's not going to be a layer one 0:02:11.540000 --> 0:02:16.380000 or layer two problem on that laptop all the way to the default gateway 0:02:16.380000 --> 0:02:20.360000 that laptop is connected to, because if it was a problem at the physical 0:02:20.360000 --> 0:02:25.400000 layer or the data link layer, they wouldn't have any connectivity at all. 0:02:25.400000 --> 0:02:29.560000 It wouldn't be selective connectivity, it would be no connectivity. 0:02:29.560000 --> 0:02:35.340000 So, if the issue affects all network connectivity on a single device, 0:02:35.340000 --> 0:02:41.060000 now we have troubleshoot at layer one and then layer two at the OSI model. 0:02:41.060000 --> 0:02:42.420000 So how do we do it? 0:02:42.420000 --> 0:02:47.340000 Well, let's start by troubleshooting at the physical layer on that host. 0:02:47.340000 --> 0:02:50.940000 So, whole bunch of things here we can check off the list. 0:02:50.940000 --> 0:02:54.800000 Number one, is the host device powered on? 0:02:54.800000 --> 0:02:58.900000 I know this seems like really simple, but physical layer also includes, 0:02:58.900000 --> 0:03:02.600000 is the device turned on or is it turned off? 0:03:02.600000 --> 0:03:07.480000 So, you know, this some might say is an ID10 error. 0:03:07.480000 --> 0:03:10.980000 In case you've never seen this acronym here stands for problem exists 0:03:10.980000 --> 0:03:15.060000 between keyboard and share, which is the human being. 0:03:15.060000 --> 0:03:19.920000 So, hopefully this is not the problem, but got to ask the question, is 0:03:19.920000 --> 0:03:21.680000 your device turned on? 0:03:21.680000 --> 0:03:27.240000 Now, let's assume the person does have their laptop or PC turned on, then 0:03:27.240000 --> 0:03:29.380000 we move on to the next step. 0:03:29.380000 --> 0:03:31.800000 Okay, they say they can't get onto the network. 0:03:31.800000 --> 0:03:35.280000 Well, the next question is, is their laptop, I'm assuming we're using 0:03:35.280000 --> 0:03:38.360000 a laptop here, plugged into the network cable. 0:03:38.360000 --> 0:03:43.100000 So, in other words, are we expecting this user to have a wired Ethernet 0:03:43.100000 --> 0:03:45.220000 connection into the network? 0:03:45.220000 --> 0:03:48.520000 So, they would want to look on their laptop or you'd want to look on their 0:03:48.520000 --> 0:03:51.420000 laptop and look for that little RJ45 jack. 0:03:51.420000 --> 0:03:55.300000 We talked about that one of the previous videos and say, hey, there it 0:03:55.300000 --> 0:03:59.680000 is and clearly no cable is connected to it, but there should be. 0:03:59.680000 --> 0:04:03.620000 So, now we need to find an Ethernet cable somewhere laying around, connect 0:04:03.620000 --> 0:04:08.340000 it to that port, and then connect the other end of that cable to the RJ45 0:04:08.340000 --> 0:04:11.380000 jack. So, the RJ45 jack on the side of their cube or the side of their 0:04:11.380000 --> 0:04:15.980000 office, most likely that user is not going to connect directly into a 0:04:15.980000 --> 0:04:18.960000 switch or router, because the switch or router is going to be sitting 0:04:18.960000 --> 0:04:21.500000 in a wiring closet locked away somewhere. 0:04:21.500000 --> 0:04:25.660000 So, what they're going to plug into is an RJ45 jack in their cube or in 0:04:25.660000 --> 0:04:26.860000 their training room. 0:04:26.860000 --> 0:04:31.740000 Now, just because you've plugged into cable, definitely that need to be 0:04:31.740000 --> 0:04:35.660000 there. But how do you know still at the physical layer that plugging into 0:04:35.660000 --> 0:04:38.940000 the cable is actually accomplished anything? 0:04:38.940000 --> 0:04:43.560000 Well, right here, if you plug into that cable, what you're looking for, 0:04:43.560000 --> 0:04:48.440000 as we see here, is the nice, shiny, pretty lights. 0:04:48.440000 --> 0:04:51.980000 So, on the side of that laptop, you should see some sort of LEDs start 0:04:51.980000 --> 0:04:55.580000 blinking, just like you see right there, which indicates that there is 0:04:55.580000 --> 0:04:58.980000 actually electrical connectivity across that cable. 0:04:58.980000 --> 0:05:04.100000 If you plug in that cable and you don't see any LEDs, it just stays dark. 0:05:04.100000 --> 0:05:07.680000 Well, then that means either the other end of the cable, wherever that 0:05:07.680000 --> 0:05:10.860000 cable goes, is not connected to anything. 0:05:10.860000 --> 0:05:16.440000 Or it is connected to something, but what it's connected to is not operational. 0:05:16.440000 --> 0:05:17.180000 And we'll get to that. 0:05:17.180000 --> 0:05:18.600000 We'll get to that. 0:05:18.600000 --> 0:05:24.020000 So, if you plug in the ethernet cable and there's no lights, now you, 0:05:24.020000 --> 0:05:27.880000 as the network administrator, as the field engineer, you have to trace 0:05:27.880000 --> 0:05:30.680000 that cable. You have to say, okay, it clearly goes into the side of this 0:05:30.680000 --> 0:05:32.300000 jack here in the wall. 0:05:32.300000 --> 0:05:33.660000 Where does it go on the other side? 0:05:33.660000 --> 0:05:36.680000 You'll have to get out your topology diagrams or somehow figure out where 0:05:36.680000 --> 0:05:40.320000 the cable on the other side of that cube or wall, where it finally goes 0:05:40.320000 --> 0:05:43.180000 and terminates in most likely a switch. 0:05:43.180000 --> 0:05:46.080000 You'll probably connect to an ethernet switch somewhere. 0:05:46.080000 --> 0:05:49.660000 Now, while we're talking about Wi-Fi, since Wi-Fi is becoming much more 0:05:49.660000 --> 0:05:53.800000 prevalent than wired ethernet these days, same type of thing. 0:05:53.800000 --> 0:05:55.320000 Physical layer now. 0:05:55.320000 --> 0:05:58.740000 On a lot of laptops, there's a physical little switch somewhere on the 0:05:58.740000 --> 0:06:03.580000 laptop that actually can turn on and turn off the Wi-Fi nitcard within 0:06:03.580000 --> 0:06:05.600000 that laptop. So, look for that. 0:06:05.600000 --> 0:06:07.500000 Like in this case, it's on the side here. 0:06:07.500000 --> 0:06:10.760000 And if it's red like this, that means, hey, that switch is in the off 0:06:10.760000 --> 0:06:14.120000 position. It may have been accidental, who knows. 0:06:14.120000 --> 0:06:18.000000 But you've got to turn that Wi-Fi nitcard on, otherwise it can't work. 0:06:18.000000 --> 0:06:25.160000 So, turn on and wait like a minute or so, and you should hopefully have 0:06:25.160000 --> 0:06:27.840000 connectivity restored. 0:06:27.840000 --> 0:06:33.000000 Now, there's another way that a nitcard, both a Wi-Fi nitcard and a regular 0:06:33.000000 --> 0:06:37.240000 LAN connected to an ethernet cable nit could be turned off. 0:06:37.240000 --> 0:06:39.180000 And that is within software. 0:06:39.180000 --> 0:06:42.960000 All operating systems, certainly all flavors of Windows, have the ability 0:06:42.960000 --> 0:06:46.840000 within software to actually disable your nitcard. 0:06:46.840000 --> 0:06:48.840000 So, that would be the next thing you'd want to check. 0:06:48.840000 --> 0:06:53.600000 You say, okay, the cable's plugged in, not getting any lights. 0:06:53.600000 --> 0:06:56.820000 I've traced it. It is connected on the other end to whatever it's supposed 0:06:56.820000 --> 0:07:01.700000 to be. The Wi-Fi nitcard, I made sure on the exterior of the laptop, I 0:07:01.700000 --> 0:07:03.180000 found that little switch. 0:07:03.180000 --> 0:07:04.760000 It is in the on position. 0:07:04.760000 --> 0:07:07.720000 And I look up at the ceiling and I see the Wi-Fi access point. 0:07:07.720000 --> 0:07:09.260000 It's got lights on it. 0:07:09.260000 --> 0:07:11.540000 Clearly, it is turned on. 0:07:11.540000 --> 0:07:15.660000 Now we need to go into the software of the device. 0:07:15.660000 --> 0:07:20.460000 So, basically the way that you're going to do this is, I've got some screen 0:07:20.460000 --> 0:07:21.960000 shots here of this. 0:07:21.960000 --> 0:07:27.260000 Now, this is showing you from Windows 10, but the procedure is pretty 0:07:27.260000 --> 0:07:29.840000 much the same in all flavors of Windows. 0:07:29.840000 --> 0:07:33.520000 You'll somehow find your way into the control panel of Windows. 0:07:33.520000 --> 0:07:36.640000 So, Windows 10, right from there from the start, and you've got the little 0:07:36.640000 --> 0:07:39.760000 gear wheel, little fly wheel there, and that will help you get into the 0:07:39.760000 --> 0:07:43.660000 settings. Once you click on that, you'll want to click on where it says 0:07:43.660000 --> 0:07:48.040000 Network and Internet, and then you'll want to find where it says Change 0:07:48.040000 --> 0:07:52.860000 Adapter Options, and right there, you can see, hey, look at that. 0:07:52.860000 --> 0:07:57.500000 My ethernet card is disabled, so I want to select, I want to right click 0:07:57.500000 --> 0:08:01.340000 on that and select the Enable box. 0:08:01.340000 --> 0:08:05.940000 So, whether it's a Wi-Fi nit or a wired nit, it could potentially be disabled 0:08:05.940000 --> 0:08:10.500000 in software, so that would be the next thing that you'd want to check. 0:08:10.500000 --> 0:08:12.500000 Okay, so let's say you've checked all that. 0:08:12.500000 --> 0:08:15.320000 What else at the physical layer could it possibly be? 0:08:15.320000 --> 0:08:21.480000 Well, maybe they actually do have an ethernet cable, so we're going back 0:08:21.480000 --> 0:08:23.800000 to wired network connectivity now. 0:08:23.800000 --> 0:08:25.460000 What's the wrong cable type? 0:08:25.460000 --> 0:08:28.560000 So, back in, I believe it was section one of these videos here. 0:08:28.560000 --> 0:08:31.720000 We talked about ethernet cables and how there's something called straight 0:08:31.720000 --> 0:08:34.620000 through and crossover cables. 0:08:34.620000 --> 0:08:41.040000 Now, most Wi-Fi nic adapters these days are smart enough to where this 0:08:41.040000 --> 0:08:42.120000 isn't really an issue. 0:08:42.120000 --> 0:08:47.480000 If you plug in the wrong kind of cable using this thing called MDIX, it 0:08:47.480000 --> 0:08:51.700000 can automatically detect that, and internally, electrically, it can adjust 0:08:51.700000 --> 0:08:52.920000 itself for that. 0:08:52.920000 --> 0:08:56.780000 But you can't guarantee, you can't bank on that, not all nic cards support 0:08:56.780000 --> 0:09:00.160000 that. So, remember, rule of thumb, you need to know the difference between 0:09:00.160000 --> 0:09:01.480000 a straight through and a crossover cable. 0:09:01.480000 --> 0:09:02.900000 We already talked about that. 0:09:02.900000 --> 0:09:04.720000 I'm not going to go into that in great detail. 0:09:04.720000 --> 0:09:07.760000 And since we're talking about the host device here, it really depends 0:09:07.760000 --> 0:09:09.660000 on what the host is connected to. 0:09:09.660000 --> 0:09:15.000000 Now, like I said, nine times out of ten, that laptop per PC will be connected 0:09:15.000000 --> 0:09:19.940000 to a wired ethernet to most likely an ethernet switch. 0:09:19.940000 --> 0:09:23.600000 So, when you're going from a laptop to a switch, which of these two cables 0:09:23.600000 --> 0:09:26.700000 do you think you should see connected there? 0:09:26.700000 --> 0:09:29.180000 Well, hopefully you said straight through. 0:09:29.180000 --> 0:09:30.040000 That would be correct. 0:09:30.040000 --> 0:09:33.620000 From a laptop to a switch or from a PC to a switch, you have using a straight 0:09:33.620000 --> 0:09:38.660000 through cable. On the very rare circumstances, where a laptop per PC might 0:09:38.660000 --> 0:09:42.640000 be directly connected into an interface on a router, then you will be 0:09:42.640000 --> 0:09:44.660000 looking for a crossover cable. 0:09:44.660000 --> 0:09:49.180000 So, maybe the cable was wrong, and that's why you're not getting any connectivity. 0:09:49.180000 --> 0:09:52.520000 So, that's pretty much it at the physical layer of the host. 0:09:52.520000 --> 0:09:56.880000 If you've checked off all of that stuff, the last thing is possibly a 0:09:56.880000 --> 0:10:01.240000 bad cable. It's theoretically possible that the cable you have has been 0:10:01.240000 --> 0:10:03.700000 damaged in some way. 0:10:03.700000 --> 0:10:05.160000 Try moving it around. 0:10:05.160000 --> 0:10:08.700000 You might see the LEDs come on and go off, indicating that some of the 0:10:08.700000 --> 0:10:10.380000 cable is broken somewhere. 0:10:10.380000 --> 0:10:11.600000 So, try swapping it out. 0:10:11.600000 --> 0:10:14.180000 Find another cable, try putting it in there. 0:10:14.180000 --> 0:10:17.840000 And if you've ruled that out, at that point, we're done with physical 0:10:17.840000 --> 0:10:20.320000 layer issues. At least on the host. 0:10:20.320000 --> 0:10:23.500000 At this point, there's no more layer one issues to troubleshoot on the 0:10:23.500000 --> 0:10:26.440000 host. So, now we move to layer two issues. 0:10:26.440000 --> 0:10:31.180000 Now, on the host device, the laptop or the PC, there's not a lot of stuff 0:10:31.180000 --> 0:10:34.820000 that can go wrong at layer two at the data link layer. 0:10:34.820000 --> 0:10:36.200000 There's a couple of things, though. 0:10:36.200000 --> 0:10:39.820000 So, let's just talk about what those might be. 0:10:39.820000 --> 0:10:42.780000 So, number one, Ethernet duplex. 0:10:42.780000 --> 0:10:45.440000 So, if you've never heard this term before, I'm not going to go into the 0:10:45.440000 --> 0:10:49.460000 great details of how Ethernet works. 0:10:49.460000 --> 0:10:54.260000 But, when Ethernet was first developed, the rules of Ethernet said, when 0:10:54.260000 --> 0:10:57.780000 one device is transmitting onto the cable, when it's sending its electrical 0:10:57.780000 --> 0:11:01.680000 energy on the cable, all the other devices connected to that same cable 0:11:01.680000 --> 0:11:03.500000 have to be quiet. 0:11:03.500000 --> 0:11:07.820000 That's called half duplex, where only one device can talk at a time. 0:11:07.820000 --> 0:11:09.580000 All the other devices have to be listening. 0:11:09.580000 --> 0:11:14.440000 If two devices are half duplex, do talk at the same time, their electrical 0:11:14.440000 --> 0:11:18.000000 signals run into each other and become meaningless garbage. 0:11:18.000000 --> 0:11:21.300000 That's called a collision, which would definitely destroy any chances 0:11:21.300000 --> 0:11:24.040000 you have of sending or receiving data. 0:11:24.040000 --> 0:11:30.080000 Now, these days, most NIT cards support what's called auto negotiation, 0:11:30.080000 --> 0:11:34.180000 which means that as soon as the NIT card detects electrical connectivity, 0:11:34.180000 --> 0:11:35.860000 some signaling goes back and forth. 0:11:35.860000 --> 0:11:36.920000 This all happens in the background. 0:11:36.920000 --> 0:11:39.720000 You as a human being don't have to do anything. 0:11:39.720000 --> 0:11:42.500000 The signaling goes back and forth between the NIT card and your laptop 0:11:42.500000 --> 0:11:47.240000 or PC, and most likely the switch port it's connected to. 0:11:47.240000 --> 0:11:51.000000 And they automatically decide what duplex they want to talk in. 0:11:51.000000 --> 0:11:54.060000 Now, most likely, if you're connected directly to a switch port, auto 0:11:54.060000 --> 0:11:58.400000 negotiation will negotiate for you what's called full duplex, which means 0:11:58.400000 --> 0:12:02.060000 you and the switch can talk at exactly the same time. 0:12:02.060000 --> 0:12:05.160000 Remember, when you looked at ethernet cabling, how I told you how ethernet 0:12:05.160000 --> 0:12:10.640000 cable is actually multiple strands of wire paired up and rolled up inside 0:12:10.640000 --> 0:12:12.640000 one physical cable. 0:12:12.640000 --> 0:12:15.740000 So full duplex simply means that while I'm transmitting electrical signals 0:12:15.740000 --> 0:12:20.520000 on my transmit pin, the switch can also, if it wants to, transmit data 0:12:20.520000 --> 0:12:24.720000 back to me on its transmit pin, because these are two separate wires. 0:12:24.720000 --> 0:12:25.580000 They don't actually talk. 0:12:25.580000 --> 0:12:28.420000 So full duplex is okay in that environment. 0:12:28.420000 --> 0:12:34.600000 Where duplex could be a potential issue would be if there's a duplex mismatch. 0:12:34.600000 --> 0:12:39.600000 So if you have one side that's running at half duplex and the other that's 0:12:39.600000 --> 0:12:43.440000 running at full duplex, that's not going to kill your connection. 0:12:43.440000 --> 0:12:45.580000 That won't stop you dead in the water. 0:12:45.580000 --> 0:12:49.020000 But what that could mean is, let's say this is the half duplex side. 0:12:49.020000 --> 0:12:52.780000 What that translates to is the full duplex side says, oh, I can talk whenever 0:12:52.780000 --> 0:12:56.500000 I want. Full duplex says, I don't have to worry about collisions. 0:12:56.500000 --> 0:12:58.540000 I can talk whenever I want. 0:12:58.540000 --> 0:13:02.660000 Whereas the half duplex side says, I can only talk when this guy's not 0:13:02.660000 --> 0:13:06.100000 talking. When he's quiet, it's my turn. 0:13:06.100000 --> 0:13:10.140000 So if I have full duplex on one side and half duplex on the other, you 0:13:10.140000 --> 0:13:14.000000 could have a situation where every time this guy wants to send data, he 0:13:14.000000 --> 0:13:18.600000 says, oh, I can't. 0:13:18.600000 --> 0:13:22.420000 And so you end up having a very, very slow network connectivity. 0:13:22.420000 --> 0:13:25.540000 Every once in a while he'll be able to squeak in there and put an ethernet 0:13:25.540000 --> 0:13:28.300000 frame on the wire when this guy is idle. 0:13:28.300000 --> 0:13:32.280000 But if this guy is transmitting a lot, it means he's going to be waiting 0:13:32.280000 --> 0:13:35.880000 a lot. And maybe dropping ethernet frames because he just can't get them 0:13:35.880000 --> 0:13:39.860000 on the wire. He's not smart enough to realize, hey, you can transmit the 0:13:39.860000 --> 0:13:41.560000 same time he can. 0:13:41.560000 --> 0:13:42.780000 Full duplex is okay. 0:13:42.780000 --> 0:13:46.320000 But if I have a duplex mismatch, he doesn't know that. 0:13:46.320000 --> 0:13:48.700000 So how do I check if I have a duplex mismatch? 0:13:48.700000 --> 0:13:52.660000 Remember, if I have auto negotiation on both sides, this should not be 0:13:52.660000 --> 0:13:56.160000 an issue. Auto negotiation should take care of what the duplex should 0:13:56.160000 --> 0:14:01.060000 be. The only time this is normally an issue is if when somebody hard codes 0:14:01.060000 --> 0:14:04.400000 the duplex on one side, they go into their net card and they manually 0:14:04.400000 --> 0:14:10.260000 specify full or half duplex and that would cause a duplex mismatch on 0:14:10.260000 --> 0:14:13.180000 the other side. So how do we check that? 0:14:13.180000 --> 0:14:16.280000 Well, once again, you want to go into your control panel and you want 0:14:16.280000 --> 0:14:20.680000 to go into your network and internet settings, adapter options. 0:14:20.680000 --> 0:14:22.760000 Now in this case, you're going to want to right click on your adapter 0:14:22.760000 --> 0:14:24.920000 and select properties. 0:14:24.920000 --> 0:14:28.560000 Then from there, under your adapter, you'll want to click on the configure 0:14:28.560000 --> 0:14:32.380000 button. So when you're configuring layer one and layer two characteristics 0:14:32.380000 --> 0:14:35.100000 of your adapter, it's in that configure button. 0:14:35.100000 --> 0:14:38.760000 And when you click on that, you'll see somewhere in there. 0:14:38.760000 --> 0:14:43.920000 Now this is for my Intel 82579 LM adapter. 0:14:43.920000 --> 0:14:47.880000 So it uses a different, you know, driver than yours probably does, but 0:14:47.880000 --> 0:14:54.340000 somewhere in there, you'll have an option to change your speed and duplex. 0:14:54.340000 --> 0:14:57.380000 Leave it set to auto negotiation like we see here. 0:14:57.380000 --> 0:14:58.460000 That's the default. 0:14:58.460000 --> 0:15:04.660000 But for example, from this laptop here, I set mine to 100 megabits and 0:15:04.660000 --> 0:15:05.080000 full width of the adapter. 0:15:05.080000 --> 0:15:06.840000 So if I do 100 megabits and I'm going to do a little duplex, that would 0:15:06.840000 --> 0:15:12.920000 be a problem because the switch I'm connected to is doing auto negotiation. 0:15:12.920000 --> 0:15:16.340000 And when one device is doing auto negotiation and the other device is 0:15:16.340000 --> 0:15:20.160000 not, the one that's doing auto negotiation says, Hey, you're not telling 0:15:20.160000 --> 0:15:21.220000 me what you're doing. 0:15:21.220000 --> 0:15:23.260000 You're not giving me my auto negotiation messages. 0:15:23.260000 --> 0:15:25.700000 So I know what kind of duplex to do with you. 0:15:25.700000 --> 0:15:30.920000 And so the auto negotiation side will, by default, fall back to half duplex. 0:15:30.920000 --> 0:15:35.600000 So if I do 100 in full right here, the other side is doing auto will end 0:15:35.600000 --> 0:15:38.180000 up being 100 and half. 0:15:38.180000 --> 0:15:40.240000 And then we'll have that duplex mismatch. 0:15:40.240000 --> 0:15:45.740000 So that's a potential issue, unlikely that you'll see that, but it's possible. 0:15:45.740000 --> 0:15:49.880000 So from a wired Ethernet perspective at layer two, that's pretty much 0:15:49.880000 --> 0:15:52.820000 it. That's pretty much the only data link layer issue that you could potentially 0:15:52.820000 --> 0:15:55.320000 run into on the host side. 0:15:55.320000 --> 0:15:59.460000 If we're talking about Wi-Fi, which, like I said, is much more prevalent. 0:15:59.460000 --> 0:16:02.560000 Another thing that could be wrong is maybe the host is connected to the 0:16:02.560000 --> 0:16:07.640000 wrong SSID. Now, if you don't know anything about Wi-Fi, real brief tutorial 0:16:07.640000 --> 0:16:13.360000 here, the Wi-Fi access point that's in the ceiling is like about 10 times 0:16:13.360000 --> 0:16:17.400000 a second broadcasting out this signal saying, Hey, here's the name of 0:16:17.400000 --> 0:16:18.680000 the network you can connect to. 0:16:18.680000 --> 0:16:20.420000 Here's my network name. 0:16:20.420000 --> 0:16:23.920000 And sometimes access points will broadcast more than one network. 0:16:23.920000 --> 0:16:27.080000 This is very common, for example, if you're in a hotel, we're in a hotel 0:16:27.080000 --> 0:16:32.320000 that might have one network, which is called an SSID, one SSID, which 0:16:32.320000 --> 0:16:39.680000 is for people who've got like a frequent rewards club, like in Hilton 0:16:39.680000 --> 0:16:43.520000 chain, right? Hilton has what's called Hilton Honors. 0:16:43.520000 --> 0:16:46.700000 You can be a Hilton Honors member and collect points whenever you go to 0:16:46.700000 --> 0:16:50.020000 their hotel. So they might have an SSID just for that. 0:16:50.020000 --> 0:16:53.500000 Then they might have another SSID that access point is advertising for 0:16:53.500000 --> 0:16:57.640000 non- Hilton Honors people, just regular guests. 0:16:57.640000 --> 0:17:01.560000 And then maybe they have another SSID that's just for the employees of 0:17:01.560000 --> 0:17:05.460000 that hotel. So it's possible, especially in a hotel environment, that 0:17:05.460000 --> 0:17:08.500000 someone may have connected to the wrong SSID. 0:17:08.500000 --> 0:17:13.020000 Now, usually when that happens, what you'll see is on somewhere on your 0:17:13.020000 --> 0:17:16.920000 laptop or PC, the little indicator of your Wi-Fi will most likely have 0:17:16.920000 --> 0:17:21.620000 an exclamation point somewhere on it, like we see right here, which indicates 0:17:21.620000 --> 0:17:27.300000 that at the physical layer, you're connected to the Wi-Fi, but either 0:17:27.300000 --> 0:17:31.400000 at the data link or possibly even the network layer, something went wrong. 0:17:31.400000 --> 0:17:34.860000 You don't have full connectivity to the internet. 0:17:34.860000 --> 0:17:37.200000 So how would we find that out? 0:17:37.200000 --> 0:17:41.480000 Well, in addition to seeing that, you would just want to open up and see, 0:17:41.480000 --> 0:17:43.960000 you know, what Wi-Fi settings do you see? 0:17:43.960000 --> 0:17:46.100000 What Wi-Fi networks do you see? 0:17:46.100000 --> 0:17:49.100000 Well, you can see right here, in my particular case, I'm connected to 0:17:49.100000 --> 0:17:51.800000 Hilton Honors corporate. 0:17:51.800000 --> 0:17:53.880000 I should have been connected to this. 0:17:53.880000 --> 0:17:56.060000 I'm not a Hilton employee. 0:17:56.060000 --> 0:17:57.300000 I don't work for Hilton. 0:17:57.300000 --> 0:18:00.040000 I don't know what the password is for the Hilton Honors corporate, so 0:18:00.040000 --> 0:18:01.860000 I connected to the wrong network. 0:18:01.860000 --> 0:18:05.740000 And that means that at layer two, I didn't fully connect. 0:18:05.740000 --> 0:18:09.780000 I didn't supply all the credentials that I should. 0:18:09.780000 --> 0:18:14.200000 So within Wi-Fi, at layer two, the most common problem is an authentication 0:18:14.200000 --> 0:18:18.660000 problem. The Wi-Fi network you're connecting to is expecting some sort 0:18:18.660000 --> 0:18:22.060000 of password, and you don't have it. 0:18:22.060000 --> 0:18:24.720000 So that's as far as the host is concerned. 0:18:24.720000 --> 0:18:27.820000 We've looked at all the possible things on the host side that could be 0:18:27.820000 --> 0:18:30.460000 wrong, and what we could do to fix it. 0:18:30.460000 --> 0:18:33.840000 So let's assume for a moment that the issue is not with the host. 0:18:33.840000 --> 0:18:38.560000 So let's move on now to identify and correcting things at the physical 0:18:38.560000 --> 0:18:42.160000 layer on the network device. 0:18:42.160000 --> 0:18:46.160000 Now, in order to do this, you as the field engineer or the network admin 0:18:46.160000 --> 0:18:51.020000 are going to have to have some real basic knowledge of Cisco iOS commands 0:18:51.020000 --> 0:18:53.120000 and how they work. 0:18:53.120000 --> 0:18:58.540000 At the CCNA level is where I go into a gory detail of Cisco iOS and how 0:18:58.540000 --> 0:19:00.960000 it works and everything, but I'm just going to give you just enough right 0:19:00.960000 --> 0:19:05.360000 now that if you've got access to a router switch, you could type in one 0:19:05.360000 --> 0:19:10.400000 of the four basic commands that you see here, and extrapolate from the 0:19:10.400000 --> 0:19:12.820000 output what you're looking for. 0:19:12.820000 --> 0:19:17.240000 So quick tutorial of iOS modes. 0:19:17.240000 --> 0:19:24.180000 When you get into a Cisco iOS router or a switch, and I'm going to get 0:19:24.180000 --> 0:19:27.100000 into one right now so you can see it. 0:19:27.100000 --> 0:19:32.560000 All right, so if you connect to INE's rack rentals and you rent some time 0:19:32.560000 --> 0:19:36.480000 on our CCNA or CCMP racks, this is what you'll see. 0:19:36.480000 --> 0:19:39.680000 So you get into a device. 0:19:39.680000 --> 0:19:44.180000 I want that name as a little confusing, so let me get into this device 0:19:44.180000 --> 0:19:52.140000 right here. Okay, so when you very first get into a Cisco router switch, 0:19:52.140000 --> 0:19:56.660000 most likely you'll see some sort of a name, router for, that's just a 0:19:56.660000 --> 0:19:59.160000 descriptive name, there's no way to predict what it's going to be, but 0:19:59.160000 --> 0:20:02.360000 the main thing you're looking for is after the name, what is the symbol 0:20:02.360000 --> 0:20:07.540000 that you see? If the symbol is the greater than sign, that tells you you're 0:20:07.540000 --> 0:20:12.240000 in a particular mode called user exec mode, or sometimes it's called exec 0:20:12.240000 --> 0:20:14.860000 mode, you want to get out of that mode. 0:20:14.860000 --> 0:20:17.820000 There's really next to nothing you can do from this mode. 0:20:17.820000 --> 0:20:21.120000 Now of those four commands I just showed you, some of them you can do 0:20:21.120000 --> 0:20:23.700000 from here. Let's find out. 0:20:23.700000 --> 0:20:26.800000 One of the commands that you're going to do most frequently in troubleshooting 0:20:26.800000 --> 0:20:30.540000 is the show running dash config command. 0:20:30.540000 --> 0:20:35.440000 That particular command, not available at this mode. 0:20:35.440000 --> 0:20:41.140000 Another command, show IP interface brief. 0:20:41.140000 --> 0:20:45.780000 That output is available at this mode, so you can do that one. 0:20:45.780000 --> 0:20:48.880000 As a matter of fact, you might be wondering, well, what commands can I 0:20:48.880000 --> 0:20:50.440000 do from this mode? 0:20:50.440000 --> 0:20:53.920000 All of your verification, your monitoring commands are going to start 0:20:53.920000 --> 0:20:55.560000 with the word show. 0:20:55.560000 --> 0:20:57.120000 Show this, show that. 0:20:57.120000 --> 0:21:01.560000 What you can do is type is show and then a question mark. 0:21:01.560000 --> 0:21:05.840000 It'll display for you all the show commands are actually available to 0:21:05.840000 --> 0:21:08.640000 you at this particular level. 0:21:08.640000 --> 0:21:12.780000 Chances are, as you work more and more with Cisco iOS, the commands that 0:21:12.780000 --> 0:21:16.040000 you want to do will not be available at this level. 0:21:16.040000 --> 0:21:19.460000 You're going to want to get out of this level and go into the next level 0:21:19.460000 --> 0:21:22.940000 by typing the command enable. 0:21:22.940000 --> 0:21:24.960000 Right here, you might get stuck. 0:21:24.960000 --> 0:21:29.160000 If this is not your router or your switch, the chances are, the person 0:21:29.160000 --> 0:21:33.160000 who owns this router switch has put an enable password on here. 0:21:33.160000 --> 0:21:37.200000 When you type enable, you'll probably be prompted for a password. 0:21:37.200000 --> 0:21:40.840000 If you're fortunate, the person that is right next to you knows what that 0:21:40.840000 --> 0:21:43.980000 password is, or maybe they can shove you aside and type it in if they 0:21:43.980000 --> 0:21:45.680000 don't want to tell you what it is. 0:21:45.680000 --> 0:21:49.200000 But in my particular case, there was no password because I don't have 0:21:49.200000 --> 0:21:52.780000 one. But in pretty much all production networks, routers and switches 0:21:52.780000 --> 0:21:57.020000 have an enable password and you'll need that to get to this level right 0:21:57.020000 --> 0:22:01.040000 here. So this is called privileged exec level. 0:22:01.040000 --> 0:22:03.580000 And this is where you want to be for your troubleshooting. 0:22:03.580000 --> 0:22:08.380000 So from here, you can issue show running dash config. 0:22:08.380000 --> 0:22:14.720000 What the output of this command shows you is all of the non-default configuration 0:22:14.720000 --> 0:22:17.760000 that is in this device. 0:22:17.760000 --> 0:22:21.240000 So if you're a field service engineer or something and you're working 0:22:21.240000 --> 0:22:25.720000 closely with Cisco TAC, they might ask you to collect the output of show 0:22:25.720000 --> 0:22:28.160000 run or show running dash config. 0:22:28.160000 --> 0:22:33.440000 So once again, the series of steps was connect to the router switch, type 0:22:33.440000 --> 0:22:36.640000 enable. If you're prompted for a password, you'll have to know what that 0:22:36.640000 --> 0:22:40.080000 is. And then this type, just type show run. 0:22:40.080000 --> 0:22:43.700000 It's the same thing as show running dash config. 0:22:43.700000 --> 0:22:52.960000 Now some other commands, like I mentioned to you, show IP interface brief. 0:22:52.960000 --> 0:22:55.620000 This is also a very useful command. 0:22:55.620000 --> 0:22:58.680000 It answers questions like, you know, what interfaces does this router 0:22:58.680000 --> 0:23:01.420000 switch have? What's the naming convention? 0:23:01.420000 --> 0:23:04.920000 You know, the type and then how many numbers slash number slash number 0:23:04.920000 --> 0:23:08.880000 is there? Is the interface actually up or not? 0:23:08.880000 --> 0:23:10.260000 This is a very critical thing right here. 0:23:10.260000 --> 0:23:13.900000 These two columns, status and protocol. 0:23:13.900000 --> 0:23:17.880000 Status means physical layer. 0:23:17.880000 --> 0:23:23.740000 If it says administratively down or if it says down, that means the physical 0:23:23.740000 --> 0:23:27.700000 layer is down. That means either there's no cable at all connected to 0:23:27.700000 --> 0:23:31.120000 this device or there is a cable, but we're just not getting any kind of 0:23:31.120000 --> 0:23:32.200000 electrical signaling. 0:23:32.200000 --> 0:23:34.640000 The physical layer is down. 0:23:34.640000 --> 0:23:39.460000 The section here called protocol is for layer two. 0:23:39.460000 --> 0:23:43.760000 That tells you is your layer two encapsulation, whatever it is, Ethernet, 0:23:43.760000 --> 0:23:45.640000 PPP, frame relay. 0:23:45.640000 --> 0:23:49.100000 Is that happy? Is that okay with whatever it's connected to on the other 0:23:49.100000 --> 0:23:53.400000 side? So ideally, what you want to see is this combination right here. 0:23:53.400000 --> 0:23:56.840000 Up, up. That means everything is good. 0:23:56.840000 --> 0:24:01.400000 Any other combination other than up, up requires some sort of troubleshooting 0:24:01.400000 --> 0:24:05.940000 on your part. Any other combination means you've got a physical and or 0:24:05.940000 --> 0:24:08.020000 a data link layer issue. 0:24:08.020000 --> 0:24:12.500000 Now this command here show IP interface brief will work on all Cisco routers 0:24:12.500000 --> 0:24:15.700000 and most Cisco switches. 0:24:15.700000 --> 0:24:19.800000 Another command that's useful that is also available on Cisco routers 0:24:19.800000 --> 0:24:24.800000 and switches is the command show interface and then type in the particular 0:24:24.800000 --> 0:24:26.060000 interface you're concerned with. 0:24:26.060000 --> 0:24:30.800000 Like in this case, if I want to see fast Ethernet 00, show interface fast 0:24:30.800000 --> 0:24:37.320000 Ethernet 00. And this will give you a lot of physical and data link layer 0:24:37.320000 --> 0:24:42.220000 information. For example, not only does it show you the state of that 0:24:42.220000 --> 0:24:47.280000 interface, but shows you for example, am I doing auto negotiation? 0:24:47.280000 --> 0:24:50.920000 Is my speed and duplex automatically negotiated or was it hard set? 0:24:50.920000 --> 0:24:52.560000 We'll look at that in just a second here. 0:24:52.560000 --> 0:24:57.060000 It also shows you down here all sorts of error statistics. 0:24:57.060000 --> 0:25:00.640000 And so if you're working with Cisco's TAC, you might want to say, hey, 0:25:00.640000 --> 0:25:08.240000 I noticed on here that there's been 25 babbles. 0:25:08.240000 --> 0:25:10.860000 And so if I'm working with them, I say, ah, okay, that gives me an idea 0:25:10.860000 --> 0:25:12.260000 as to what's wrong. 0:25:12.260000 --> 0:25:17.780000 So all of this stuff is indicating some kind of physical layer problem 0:25:17.780000 --> 0:25:24.200000 or issue. Now on a switch, there's also another command that's just unique 0:25:24.200000 --> 0:25:25.520000 to switches alone. 0:25:25.520000 --> 0:25:27.340000 It's also very valuable. 0:25:27.340000 --> 0:25:35.580000 And that is the command show interface status show interface status. 0:25:35.580000 --> 0:25:40.960000 You can see here from this one command, it shows you the interface name. 0:25:40.960000 --> 0:25:44.960000 It shows you the status and what you want to see here is the word connected. 0:25:44.960000 --> 0:25:48.560000 If it doesn't say connected and that's the interface that's having problems, 0:25:48.560000 --> 0:25:52.160000 then that means you've got a physical or data link layer issue. 0:25:52.160000 --> 0:25:53.980000 It should say connected. 0:25:53.980000 --> 0:25:55.160000 It shows you your VLAN. 0:25:55.160000 --> 0:25:58.240000 If you're familiar with that, it also shows you, you know, your speed 0:25:58.240000 --> 0:25:59.660000 and your duplex. 0:25:59.660000 --> 0:26:04.280000 If you see a little A in front of it, that means it was auto negotiated. 0:26:04.280000 --> 0:26:07.480000 So now that we know those basic commands right there.