WEBVTT 0:00:07.380000 --> 0:00:11.520000 This video is going to cover the Cisco configuration register. 0:00:11.520000 --> 0:00:18.500000 My name is Keith Bogart and I will be your instructor for this video as 0:00:18.500000 --> 0:00:21.700000 well as all the other ones in the series coming up. 0:00:21.700000 --> 0:00:24.460000 And specifically what we're going to look at is the configuration register 0:00:24.460000 --> 0:00:32.860000 from the How do I use it to accomplish certain objectives? 0:00:32.860000 --> 0:00:36.920000 So let's start. What is this thing called the configuration register? 0:00:36.920000 --> 0:00:40.220000 Rouders and switches both have it. 0:00:40.220000 --> 0:00:44.760000 So the configuration register is a special set of bits located within 0:00:44.760000 --> 0:00:50.240000 NV RAM. It's 16 bits located in NV RAM that are looked at the moment the 0:00:50.240000 --> 0:00:52.800000 switch or the router is powered on. 0:00:52.800000 --> 0:00:55.840000 So really the purpose of those bits is to control some of the boot up 0:00:55.840000 --> 0:00:58.620000 characteristics of that device. 0:00:58.620000 --> 0:01:01.920000 Now there's a certain default setting for the configuration register and 0:01:01.920000 --> 0:01:03.320000 I'll show you what that is in just a moment. 0:01:03.320000 --> 0:01:07.820000 You'll certainly need to memorize that for the CCT and moving on with 0:01:07.820000 --> 0:01:10.860000 life. But there are other settings that you can have as well to control 0:01:10.860000 --> 0:01:13.100000 some of these characteristics. 0:01:13.100000 --> 0:01:14.960000 So let's take a look. 0:01:14.960000 --> 0:01:16.960000 We know that it's 16 bits in length. 0:01:16.960000 --> 0:01:19.940000 So what I've drawn here on the bottom are, I'll make this a little bit 0:01:19.940000 --> 0:01:25.280000 bigger, are the 16 bits and it's actually counted from bit 0 to bit 15. 0:01:25.280000 --> 0:01:28.620000 So whenever you see documents describing the configuration registering 0:01:28.620000 --> 0:01:32.720000 what each bit stands for, it actually won't start with bit 1. 0:01:32.720000 --> 0:01:34.600000 It'll start with bit 0. 0:01:34.600000 --> 0:01:36.120000 So just keep that in mind. 0:01:36.120000 --> 0:01:40.080000 Bit 4 here, I've already populated with a 0 because bit 4 is not used 0:01:40.080000 --> 0:01:42.940000 for anything. So it doesn't have any relevance. 0:01:42.940000 --> 0:01:44.360000 But all the other bits do. 0:01:44.360000 --> 0:01:49.700000 So let's start with bits 0 through 3. 0:01:49.700000 --> 0:01:52.100000 In other words, the first 4 bits. 0:01:52.100000 --> 0:01:56.860000 The main point of the first 4 bits is really to do is to control when 0:01:56.860000 --> 0:01:58.760000 this device boots up. 0:01:58.760000 --> 0:02:02.800000 If it's going to look for the Cisco iOS image in the normal place, which 0:02:02.800000 --> 0:02:08.300000 is flash memory, or if it's going to send out a broadcast like net boot 0:02:08.300000 --> 0:02:12.140000 request, trying to see if there's any TFTP servers out there anywhere 0:02:12.140000 --> 0:02:15.680000 that have an iOS image to download, or if it's just going to be stuck 0:02:15.680000 --> 0:02:21.040000 in Ramon. So that is bits 0 through 3. 0:02:21.040000 --> 0:02:25.920000 And the default setting of those bits is 0010. 0:02:25.920000 --> 0:02:30.920000 So by default, in the configuration register, the last number is 2. 0:02:30.920000 --> 0:02:32.960000 And you can see here, that is 2. 0:02:32.960000 --> 0:02:35.380000 0010 is the number 2. 0:02:35.380000 --> 0:02:39.060000 Now we know that bit 4 has no significance. 0:02:39.060000 --> 0:02:46.360000 Bit number 6 causes the system software to ignore NV Ram contents. 0:02:46.360000 --> 0:02:48.160000 Now one would this be useful? 0:02:48.160000 --> 0:02:51.680000 Later on, I'll show you a video about how to do password recovery on a 0:02:51.680000 --> 0:02:55.520000 Cisco device. But this is the critical way that you accomplish that. 0:02:55.520000 --> 0:03:00.580000 If you don't know what the enable password or the enable secret is of 0:03:00.580000 --> 0:03:04.080000 your device, number one, you've got to be physically right next to it. 0:03:04.080000 --> 0:03:07.220000 There's no way to do password recovery remotely. 0:03:07.220000 --> 0:03:10.600000 Once you're physically next to it, you power cycle the device, you hit 0:03:10.600000 --> 0:03:14.660000 the break key while it's power cycling, it goes into a state called Ramon. 0:03:14.660000 --> 0:03:15.460000 And it'll actually say that. 0:03:15.460000 --> 0:03:17.460000 It'll say Ramon next to it. 0:03:17.460000 --> 0:03:21.400000 Now from Ramon, you can change your configuration register. 0:03:21.400000 --> 0:03:23.440000 And I'll show you how to do that in just a moment. 0:03:23.440000 --> 0:03:32.040000 But the key point is, if you set bit number 6 to a 1, that tells the device, 0:03:32.040000 --> 0:03:36.460000 hey, when I reset you, when I reload you, ignore the startup configuration 0:03:36.460000 --> 0:03:39.540000 file. Just bypass it entirely. 0:03:39.540000 --> 0:03:42.920000 And that will give you a way to get into a enable mode of your router 0:03:42.920000 --> 0:03:46.480000 switch, because it doesn't have the startup configuration file to look 0:03:46.480000 --> 0:03:52.560000 for. Now by default, that bit is set to zero, which means do not ignore 0:03:52.560000 --> 0:03:59.780000 NV Ram. Go in there, look at your startup configuration, and pull that. 0:03:59.780000 --> 0:04:03.980000 Now bit 7, this is sort of a nebulous bit that took me a little bit a 0:04:03.980000 --> 0:04:06.300000 little while to understand what this was. 0:04:06.300000 --> 0:04:10.340000 By default, bit 7 is set to a zero. 0:04:10.340000 --> 0:04:15.340000 If you turn it on to a 1, this does something which calls, enables the 0:04:15.340000 --> 0:04:19.000000 original equipment manufacturer bit. 0:04:19.000000 --> 0:04:20.440000 What does that mean? 0:04:20.440000 --> 0:04:22.480000 Well, I did a little bit of testing here. 0:04:22.480000 --> 0:04:24.740000 And this is what I found. 0:04:24.740000 --> 0:04:29.740000 So the OEM bit, we'll expand this. 0:04:29.740000 --> 0:04:34.740000 So this shows you what all the output is that you'll see when your Cisco 0:04:34.740000 --> 0:04:39.580000 iOS router or switch boots normally, when you power cycle it, when you 0:04:39.580000 --> 0:04:43.880000 reload it. I thought, well, what would happen if I set that OEM bit? 0:04:43.880000 --> 0:04:47.720000 What if I changed my configuration register so that bit was a 1? 0:04:47.720000 --> 0:04:48.500000 And here's what it does. 0:04:48.500000 --> 0:04:55.140000 If you go down right here, this section right here, that's normal. 0:04:55.140000 --> 0:04:56.580000 That's the default behavior. 0:04:56.580000 --> 0:05:02.040000 If you set the OEM bit, that section is not displayed. 0:05:02.040000 --> 0:05:05.620000 Now, it kind of brings to mind the question, why would I want to do that? 0:05:05.620000 --> 0:05:09.140000 Why would I not want to display that little section when booting up my 0:05:09.140000 --> 0:05:11.140000 router switch? I don't know. 0:05:11.140000 --> 0:05:12.820000 You'll have to answer that question for yourself. 0:05:12.820000 --> 0:05:18.620000 But that was the only actionable effect I saw when I set the OEM bit. 0:05:18.620000 --> 0:05:21.560000 Was it this section that I have highlighted here was not displayed? 0:05:21.560000 --> 0:05:24.940000 It was hidden when my router switch was loaded. 0:05:24.940000 --> 0:05:28.720000 So the long and short of it is, there's probably not much of a reason 0:05:28.720000 --> 0:05:32.560000 to mate to screw around with the OEM bit. 0:05:32.560000 --> 0:05:40.000000 All right, bit eight, disables the break function. 0:05:40.000000 --> 0:05:42.080000 Now, what does that mean? 0:05:42.080000 --> 0:05:45.580000 So this bit is set to a 1. 0:05:45.580000 --> 0:05:50.200000 Now, what that means is, disables the break function. 0:05:50.200000 --> 0:05:58.300000 So when you are booting up a router or a switch, there's a long time when 0:05:58.300000 --> 0:06:02.280000 it's displaying all these messages like you just saw in that text document 0:06:02.280000 --> 0:06:04.920000 just described to you. 0:06:04.920000 --> 0:06:13.620000 So when this bit is set to a 1, that means that the break function is 0:06:13.620000 --> 0:06:16.140000 only going to be workable. 0:06:16.140000 --> 0:06:20.680000 It's only going to take effect within the first probably 10 seconds or 0:06:20.680000 --> 0:06:23.200000 so of the boot up process. 0:06:23.200000 --> 0:06:27.500000 In other words, if you want to break into Raman, you've got about 10 seconds 0:06:27.500000 --> 0:06:33.300000 to do when the device first boots up. 0:06:33.300000 --> 0:06:35.540000 So that means that the break sequence on your keyboard, it's ignoring 0:06:35.540000 --> 0:06:38.120000 it. That's what that bit stands for. 0:06:38.120000 --> 0:06:41.240000 If that bit is a zero, that means the break key or the break sequence 0:06:41.240000 --> 0:06:45.660000 will work at any point in time when you're during the boot up cycle, when 0:06:45.660000 --> 0:06:47.100000 you're trying to get into Raman. 0:06:47.100000 --> 0:06:48.460000 So that's all that means. 0:06:48.460000 --> 0:06:53.240000 And the default setting there is one bit number nine, which is also zero 0:06:53.240000 --> 0:06:56.200000 says use a secondary bootstrap. 0:06:56.200000 --> 0:06:59.940000 So when that's set to a zero, that means do not use a secondary bootstrap. 0:06:59.940000 --> 0:07:05.100000 From everything I saw from all the research I did, vast majority, 99% 0:07:05.100000 --> 0:07:09.040000 of all the Cisco riders and switches do not use a secondary bootstrap 0:07:09.040000 --> 0:07:12.980000 and they advise against setting this bit. 0:07:12.980000 --> 0:07:15.580000 So you should never set bit number nine. 0:07:15.580000 --> 0:07:17.840000 There's no reason to do that. 0:07:17.840000 --> 0:07:20.560000 A secondary bootstrap for those of you who are a little curious as to 0:07:20.560000 --> 0:07:26.440000 what it is, is that a long time ago, long time ago in the age of computers, 0:07:26.440000 --> 0:07:32.560000 a primary bootstrap was like 10 basic lines of real basic code that used 0:07:32.560000 --> 0:07:35.520000 to be, they used to plug it in and like a punch card of a real simple 0:07:35.520000 --> 0:07:40.760000 computer. And those first initial 10 lines of code help the computer know 0:07:40.760000 --> 0:07:43.680000 how am I supposed to read my disk drive? 0:07:43.680000 --> 0:07:47.440000 How exactly do I read a disk drive so I can keep going, so I can keep 0:07:47.440000 --> 0:07:51.260000 booting up? That was called the initial bootstrap. 0:07:51.260000 --> 0:07:54.960000 And then a secondary bootstrap would be one that followed on after that, 0:07:54.960000 --> 0:07:58.500000 that gave even more instructions on how to boot up. 0:07:58.500000 --> 0:08:02.580000 Well these days in these routers and switches, there is no secondary bootstrap. 0:08:02.580000 --> 0:08:06.540000 The primary bootstrap is everything the router switch needs to know to 0:08:06.540000 --> 0:08:10.760000 be able to load its software to read its disk drives and everything else. 0:08:10.760000 --> 0:08:13.620000 So there's no need to set that bit. 0:08:13.620000 --> 0:08:20.600000 So bit 10 and another bit which I'll talk about, which is bit 11, I'm 0:08:20.600000 --> 0:08:23.960000 going to talk about on a subsequent slide, that controls actually bit 0:08:23.960000 --> 0:08:31.020000 10 and 14 talk about broadcast usages. 0:08:31.020000 --> 0:08:33.360000 And I'll have that on the other side, I'm going to skip that for right 0:08:33.360000 --> 0:08:37.720000 now, just know that 10 and 14 by default are set to zero. 0:08:37.720000 --> 0:08:44.400000 Now bits 5, 11 and 12 can be important to you. 0:08:44.400000 --> 0:08:47.640000 This describes the baud rate of the console. 0:08:47.640000 --> 0:08:50.740000 So if you're connected to the console, you've probably heard, you've probably 0:08:50.740000 --> 0:08:54.080000 read a lot of documents that say, hey, if you want to connect to the console, 0:08:54.080000 --> 0:09:00.060000 the router switch, the numbers you got to memorize are 96, 8, none and 0:09:00.060000 --> 0:09:07.440000 one. In other words, 96 baud rate, 8 data bits, no stop bits, 8, none, 0:09:07.440000 --> 0:09:13.000000 one parity bit, 8, none one, and then no flow control. 0:09:13.000000 --> 0:09:16.000000 But the main thing is that 9,600 was the baud. 0:09:16.000000 --> 0:09:17.620000 That's the default baud. 0:09:17.620000 --> 0:09:19.160000 Well, what if I want to change that? 0:09:19.160000 --> 0:09:22.580000 What if I want to make the baud rate faster or slower? 0:09:22.580000 --> 0:09:24.920000 The combination of these three bits would allow you to do that. 0:09:24.920000 --> 0:09:28.380000 In the next slide, I'll show you what all the permutations are for affecting 0:09:28.380000 --> 0:09:36.480000 that. Bit 13, which is set to one by default, says boot the default flash 0:09:36.480000 --> 0:09:40.560000 software if the network boot fails. 0:09:40.560000 --> 0:09:43.860000 So if it tries to do network boot and that fails, boot the regular iOS 0:09:43.860000 --> 0:09:48.360000 and that is the default behavior. 0:09:48.360000 --> 0:09:53.100000 And then 14, I talked about broadcast, we'll get to that in the next slide. 0:09:53.100000 --> 0:09:58.660000 And then 15 enables diagnostic messages and ignores the contents of NV 0:09:58.660000 --> 0:10:03.200000 RAM. This is another bit that I thought, hmm, nobody ever talks about 0:10:03.200000 --> 0:10:07.040000 Bit 15. What diagnostic messages are they talking about? 0:10:07.040000 --> 0:10:10.920000 What happens if you enable Bit 15 in your configuration register? 0:10:10.920000 --> 0:10:13.220000 Well, it says ignores the contents of NV RAM. 0:10:13.220000 --> 0:10:14.860000 So that seems pretty clear. 0:10:14.860000 --> 0:10:18.700000 That means if you've got a startup config, it will ignore it. 0:10:18.700000 --> 0:10:21.500000 But what are these diagnostic messages it's talking about? 0:10:21.500000 --> 0:10:23.000000 Well, I did an experiment. 0:10:23.000000 --> 0:10:27.420000 I set my configuration register, I turned on bit 15, and let me show you 0:10:27.420000 --> 0:10:29.780000 what the results were of that. 0:10:29.780000 --> 0:10:34.920000 So here is with bit 15 set. 0:10:34.920000 --> 0:10:39.900000 So the first stuff here is pretty much the same, but you'll notice there's 0:10:39.900000 --> 0:10:45.980000 a lot of stuff you can see when your device is booting up. 0:10:45.980000 --> 0:10:50.480000 All sorts of information about, it looks to me like memory sections, although 0:10:50.480000 --> 0:10:53.660000 I don't know what this stuff is talking about, but there may be certain 0:10:53.660000 --> 0:10:57.060000 situations when the Cisco TAC needs to see this. 0:10:57.060000 --> 0:11:01.340000 But this is all the information, this diagnostic information, this displayed 0:11:01.340000 --> 0:11:08.700000 when you enable bit 15 in your configuration register. 0:11:08.700000 --> 0:11:11.500000 So clearly it's not something you would normally have to do and you can 0:11:11.500000 --> 0:11:15.480000 see down here below it's ignoring the startup configuration file. 0:11:15.480000 --> 0:11:18.340000 It's giving me my initial configuration dialogue, even though I actually 0:11:18.340000 --> 0:11:21.560000 did have a startup configuration file. 0:11:21.560000 --> 0:11:25.780000 So I've never heard of a case where somebody was advised to enable bit 0:11:25.780000 --> 0:11:30.760000 15 where all of this stuff was necessary, but I suppose it probably does 0:11:30.760000 --> 0:11:35.240000 exist. And now you know, after watching this video, what type of stuff 0:11:35.240000 --> 0:11:38.860000 you'll see if you enable bit 15. 0:11:38.860000 --> 0:11:44.660000 So let's go into a little bit more detail now about the console baud rate. 0:11:44.660000 --> 0:11:50.200000 So we know that there's three bits that determine that, 12, 11, and 5. 0:11:50.200000 --> 0:11:52.420000 Now I'll give you a little caveat here. 0:11:52.420000 --> 0:11:56.120000 A lot of documents out there on the Cisco configuration register only 0:11:56.120000 --> 0:11:58.440000 mention bits 12 and 11. 0:11:58.440000 --> 0:12:01.980000 They say that only bits 12 and 11 are for the console rate, and clearly 0:12:01.980000 --> 0:12:08.980000 if I only have bits of bauds. 0:12:08.980000 --> 0:12:12.120000 But I did find this one little hidden document, this little gem tucked 0:12:12.120000 --> 0:12:15.640000 away that also explained that bit 5 was relevant. 0:12:15.640000 --> 0:12:20.080000 And after going through that document and performing my tests, sure enough, 0:12:20.080000 --> 0:12:23.120000 there are actually eight combinations of baud. 0:12:23.120000 --> 0:12:25.360000 And here you can see what they are. 0:12:25.360000 --> 0:12:27.280000 I'll go ahead and expand this a little bit. 0:12:27.280000 --> 0:12:33.080000 So when you have the default configuration register of 0x21.02, so this 0:12:33.080000 --> 0:12:33.680000 will be the default. 0:12:33.680000 --> 0:12:37.700000 If you never touch it, this is the default setting. 0:12:37.700000 --> 0:12:44.420000 You can see that bits 12, 11, and 5, which specify your console baud rate 0:12:44.420000 --> 0:12:48.980000 are 0, 0, 0, which is set to the default of 9,600. 0:12:48.980000 --> 0:12:53.640000 However, if you change in those bits to anything else, you can see what 0:12:53.640000 --> 0:12:55.540000 the resulting combinations are. 0:12:55.540000 --> 0:13:01.680000 You can actually go all the way up to a baud rate of 115,200. 0:13:01.680000 --> 0:13:05.000000 Now, a little caveat about this one. 0:13:05.000000 --> 0:13:09.920000 In the lab, I tried from the normal Cisco iOS command prompt, and I'll 0:13:09.920000 --> 0:13:14.840000 show you what the command is for that in just a second, to change my configuration 0:13:14.840000 --> 0:13:22.100000 register so that bits 12, 11, and 5 were set and turned on. 0:13:22.100000 --> 0:13:31.280000 I believe that actually gave me a configuration register of 0x3922. 0:13:31.280000 --> 0:13:36.260000 If I do 3922, then those three bits in red are turned on. 0:13:36.260000 --> 0:13:37.380000 And it wouldn't take it. 0:13:37.380000 --> 0:13:38.820000 In other words, it did take it. 0:13:38.820000 --> 0:13:40.560000 It didn't give me any error messages. 0:13:40.560000 --> 0:13:43.020000 But when it booted up, nothing was changed. 0:13:43.020000 --> 0:13:44.580000 It was still 9,600. 0:13:44.580000 --> 0:13:47.360000 And when I looked at it, it still said 2,102. 0:13:47.360000 --> 0:13:51.940000 The only way I could actually get it to accept that special number where 0:13:51.940000 --> 0:13:56.780000 those three bits were turned on is if I broke into Ramon first during 0:13:56.780000 --> 0:14:02.440000 the boot up process, change the configuration register from Ramon, then 0:14:02.440000 --> 0:14:06.560000 I was able to get that baud rate of 115,200. 0:14:06.560000 --> 0:14:09.980000 I have not tried it with the other numbers on this list. 0:14:09.980000 --> 0:14:13.120000 So I'm just warning you, there are certain numbers on this list that may 0:14:13.120000 --> 0:14:17.200000 not work from regular Cisco iOS command mode. 0:14:17.200000 --> 0:14:20.860000 You might have to go into Ramon mode to get the settings to match the 0:14:20.860000 --> 0:14:22.300000 diagram that you see here. 0:14:22.300000 --> 0:14:27.080000 But I can verify I have tested it with the highest number 115,200. 0:14:27.080000 --> 0:14:29.280000 And that does indeed work. 0:14:29.280000 --> 0:14:32.180000 So if you're trying to do some sort of disaster recovery or something, 0:14:32.180000 --> 0:14:37.860000 trying to download, for example, a Cisco iOS image over the console port, 0:14:37.860000 --> 0:14:39.160000 right? This is something you need to know. 0:14:39.160000 --> 0:14:43.020000 What if somebody blows away your iOS and in your flash memory, you have 0:14:43.020000 --> 0:14:48.000000 no iOS. Well, then you have to use something called X modem or Y modem 0:14:48.000000 --> 0:14:51.920000 to download your iOS image over the console port. 0:14:51.920000 --> 0:14:59.020000 Well, iOS images can easily be 30, 40, 50 megabits in size or bigger. 0:14:59.020000 --> 0:15:04.180000 And that will take forever to do if you're doing 96, 100, and 96, 100, 0:15:04.180000 --> 0:15:06.120000 you're talking about hours to download it. 0:15:06.120000 --> 0:15:09.580000 So that would be a classic case where first you'd want to change your 0:15:09.580000 --> 0:15:14.920000 configuration register to get the highest baud rate possible of 115, 200. 0:15:14.920000 --> 0:15:18.580000 And then that'll dramatically speed up anything you have to download across 0:15:18.580000 --> 0:15:20.120000 the console port. 0:15:20.120000 --> 0:15:29.260000 Now I also want to talk about the bits of 14 and 10 that reference the 0:15:29.260000 --> 0:15:30.720000 broadcast usage. 0:15:30.720000 --> 0:15:35.640000 You may have seen some circumstances where you powered on a router switch 0:15:35.640000 --> 0:15:39.060000 and it's kind of irritating because you had to wait for a while because 0:15:39.060000 --> 0:15:42.820000 it would said looking for service dash config and sending out a bunch 0:15:42.820000 --> 0:15:49.980000 of broadcasts. So routers and switches can be configured that when they 0:15:49.980000 --> 0:15:53.740000 boot up, they will automatically all on the road start sending out these 0:15:53.740000 --> 0:15:59.080000 broadcasts saying, hey, is there a TFTP or an FTP server out there? 0:15:59.080000 --> 0:16:03.960000 I need to get a config called default config where they're trying to download 0:16:03.960000 --> 0:16:06.300000 their config via a server. 0:16:06.300000 --> 0:16:09.720000 And then if that doesn't exist, well, then you just have to wait for it 0:16:09.720000 --> 0:16:12.980000 to time out, which takes about two or three minutes before you finally 0:16:12.980000 --> 0:16:15.280000 get access to the console port. 0:16:15.280000 --> 0:16:20.220000 So what these bits are controlling is when that happens, when the router 0:16:20.220000 --> 0:16:24.340000 or switch decides to send out its own broadcast because it's trying to 0:16:24.340000 --> 0:16:29.200000 retrieve a file or retrieve some software, what do you want the format 0:16:29.200000 --> 0:16:31.980000 of that broadcast to be? 0:16:31.980000 --> 0:16:37.780000 Now, by default, these bits are both set to zero. 0:16:37.780000 --> 0:16:43.280000 Bit 14 and 10 is set to zero, which means the broadcast is all ones, 1111. 0:16:43.280000 --> 0:16:45.380000 But you can change that. 0:16:45.380000 --> 0:16:49.480000 For example, notice here in my drawing, I have a router. 0:16:49.480000 --> 0:16:54.180000 He has an interface that has 5.111 on one interface and I've configured 0:16:54.180000 --> 0:16:57.880000 99.111 on the other interface. 0:16:57.880000 --> 0:17:04.120000 Well, if I change my configuration register to 0x6502, that is actually 0:17:04.120000 --> 0:17:08.780000 setting bit 14 and bit 10 to a 1. 0:17:08.780000 --> 0:17:12.000000 It's setting both those bits to a 1. 0:17:12.000000 --> 0:17:14.080000 Well, what happens when they're set to a 1? 0:17:14.080000 --> 0:17:18.240000 Well, when bit 14 is set to a 1, that means when it sends out a broadcast, 0:17:18.240000 --> 0:17:22.140000 it's going to retain the network number of whatever that interface is. 0:17:22.140000 --> 0:17:25.200000 So when it sends out a broadcast to the left, it'll retain the network 0:17:25.200000 --> 0:17:29.360000 number of 5. When it sends out to the right, it'll retain the network 0:17:29.360000 --> 0:17:37.220000 number of 99. When bit 10 is set to 1, that means the host portion is 0:17:37.220000 --> 0:17:39.400000 going to be all ones. 0:17:39.400000 --> 0:17:41.500000 Now, actually, I probably need to hold on a second. 0:17:41.500000 --> 0:17:42.460000 I just know something here. 0:17:42.460000 --> 0:17:47.400000 This diagram is a little wrong because based on my subnet mask, it should 0:17:47.400000 --> 0:17:49.080000 have looked something like this. 0:17:49.080000 --> 0:17:51.980000 That makes a little bit more sense because we can see that the router 0:17:51.980000 --> 0:17:56.920000 will say, oh, well, according to my subnet mask, the network is 5.1.1. 0:17:56.920000 --> 0:18:01.760000 So with bit 14 set as a 1, that means I need to retain the network of 0:18:01.760000 --> 0:18:07.560000 5.1.1. As far as the host bits are set, well, bit 10 is a 1, which means 0:18:07.560000 --> 0:18:09.500000 do not set the host bits. 0:18:09.500000 --> 0:18:10.940000 Leave them as zeros. 0:18:10.940000 --> 0:18:13.960000 So this is actually going to be sending out what's called subnet broadcasts 0:18:13.960000 --> 0:18:19.180000 because I've set bits 14 and 10 to 1. 0:18:19.180000 --> 0:18:23.040000 In the real world, I'm not sure when you would ever, ever need to change 0:18:23.040000 --> 0:18:26.940000 these bits or modify them, but I just ran across this and I thought you 0:18:26.940000 --> 0:18:28.780000 might find it kind of interesting to know. 0:18:28.780000 --> 0:18:32.360000 So last couple of slides, how do we change this thing called the configuration 0:18:32.360000 --> 0:18:34.160000 register? How do we set these bits? 0:18:34.160000 --> 0:18:36.100000 Well, you've already seen a little bit of preview of it. 0:18:36.100000 --> 0:18:41.160000 From normal iOS mode, you would just go into global configuration mode 0:18:41.160000 --> 0:18:47.020000 and use the config-register command and then set it as 0x and then four 0:18:47.020000 --> 0:18:49.720000 hexadecimal characters. 0:18:49.720000 --> 0:18:56.520000 Or if you're in Raman mode, you just say conf-reg, altogether conf-reg 0:18:56.520000 --> 0:19:00.180000 and then set your configuration register right there. 0:19:00.180000 --> 0:19:05.420000 Now what you see here are the two most common configuration register settings. 0:19:05.420000 --> 0:19:11.840000 You should definitely memorize that 0x21.02 is the default. 0:19:11.840000 --> 0:19:13.180000 That is the default. 0:19:13.180000 --> 0:19:17.020000 That means load iOS from flash as normal. 0:19:17.020000 --> 0:19:21.600000 If there is a startup configuration file in NV Ram, load that startup 0:19:21.600000 --> 0:19:26.720000 configuration file and set the baud rate to 9600. 0:19:26.720000 --> 0:19:29.880000 Those are the three main components of the default. 0:19:29.880000 --> 0:19:36.020000 Another very popular one you will see is the one on top, 0x2142. 0:19:36.020000 --> 0:19:42.020000 What is that? That basically means do everything except ignore the startup 0:19:42.020000 --> 0:19:43.700000 configuration file. 0:19:43.700000 --> 0:19:48.220000 In other words, load iOS is normal, set the baud rate to 9600. 0:19:48.220000 --> 0:19:53.320000 However, by setting that four in there, that one particular bit that we 0:19:53.320000 --> 0:19:57.760000 talked about earlier which says ignore NV Ram, ignore the startup configuration 0:19:57.760000 --> 0:20:02.160000 file. That's typically used when the startup configuration file contains 0:20:02.160000 --> 0:20:06.080000 some sort of a password that you've forgotten and you want to ignore it. 0:20:06.080000 --> 0:20:08.340000 You want to circumvent it. 0:20:08.340000 --> 0:20:12.680000 And this is how you can see the configuration register with the show version 0:20:12.680000 --> 0:20:15.380000 command at the very bottom of show version. 0:20:15.380000 --> 0:20:19.440000 It tells you what your current configuration register is and what it will 0:20:19.440000 --> 0:20:21.000000 be upon the next reload.