WEBVTT

0:00:05.620000 --> 0:00:10.260000
 Okay, so I think I know what's
 wrong with switch number one.

0:00:10.260000 --> 0:00:15.120000
 Now before I do it, let me
 go in here and show you.

0:00:15.120000 --> 0:00:24.680000
 Okay. So let's go into
 switch number one.

0:00:24.680000 --> 0:00:32.640000
 S one. Okay, right here, if you can
 see this, when I type in S one, it

0:00:32.640000 --> 0:00:35.440000
 said connection refused
 by remote host.

0:00:35.440000 --> 0:00:42.320000
 When I type in S one or R one, the
 terminal server says, okay, I need

0:00:42.320000 --> 0:00:47.840000
 to establish a new connection to S
 one, which is on octal cable one or

0:00:47.840000 --> 0:00:50.680000
 R one, which is on octal
 cable number three.

0:00:50.680000 --> 0:00:51.620000
 But here's the thing.

0:00:51.620000 --> 0:00:54.940000
 If the terminal server looks around
 and says, uh oh, there's already an

0:00:54.940000 --> 0:00:57.700000
 electrical connection on that octal
 cable, that octal cable is already

0:00:57.700000 --> 0:01:02.400000
 being used to host a console session,
 then I'll get this message.

0:01:02.400000 --> 0:01:06.520000
 This is basically saying you can't create
 a new session to S one because

0:01:06.520000 --> 0:01:09.120000
 S one already has a session to it.


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 So that my next logical question would
 be then, okay, well, which session

0:01:11.840000 --> 0:01:17.560000
 is it? And I can just do
 the show session command.

0:01:17.560000 --> 0:01:21.940000
 It says right here, okay, connection
 number one is going to S one.

0:01:21.940000 --> 0:01:23.960000
 I don't know if you can
 see that very well.

0:01:23.960000 --> 0:01:26.660000
 I think I can make that a little
 bit bigger right there.

0:01:26.660000 --> 0:01:28.840000
 Connection number one
 is going to S one.

0:01:28.840000 --> 0:01:33.440000
 So now all I have to press is the number
 one and then enter and that gets

0:01:33.440000 --> 0:01:36.660000
 me into that existing connection.

0:01:36.660000 --> 0:01:42.360000
 All right. So why is fast ethernet
 zero slash one not lighting up?

0:01:42.360000 --> 0:01:45.380000
 Why is it not giving me
 pretty colors here?

0:01:45.380000 --> 0:01:47.740000
 Show IP interface brief.

0:01:47.740000 --> 0:01:51.040000
 And if you look at my CCNA videos,
 you'll learn a lot more about that

0:01:51.040000 --> 0:01:56.360000
 command. All right.

0:01:56.360000 --> 0:02:00.940000
 So this says fast ethernet zero one
 is down down and yet I absolutely

0:02:00.940000 --> 0:02:03.300000
 do have a cable connecting to it.

0:02:03.300000 --> 0:02:06.400000
 Ah, I think I know what
 the problem is.

0:02:06.400000 --> 0:02:14.100000
 The setup here on my desk is my laptop
 is connected into a docking station.

0:02:14.100000 --> 0:02:19.640000
 When I took this cable right here, I
 connected it directly into the RJ45

0:02:19.640000 --> 0:02:22.180000
 jack of the laptop itself.

0:02:22.180000 --> 0:02:26.900000
 My suspicion is that when it's in a docking
 station, it probably deactivates

0:02:26.900000 --> 0:02:31.440000
 that because the docking station
 itself has an RJ45 jack.

0:02:31.440000 --> 0:02:35.020000
 So I bet you if I plug this into the
 docking stations, our RJ45 jack,

0:02:35.020000 --> 0:02:37.820000
 let's say, oh, yes, there it is.

0:02:37.820000 --> 0:02:42.740000
 If I can just find
 that connection.

0:02:42.740000 --> 0:02:48.640000
 Let's see here. And where is it?

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 There it is. And do
 we have success?

0:02:56.720000 --> 0:02:58.520000
 Now I see the lights going
 on on the switch.

0:02:58.520000 --> 0:03:01.200000
 So that was it. It wasn't
 a cable problem.

0:03:01.200000 --> 0:03:04.440000
 It wasn't a problem with
 the switch port.

0:03:04.440000 --> 0:03:07.140000
 Simply a fact that my laptop was
 connected to a docking station.

0:03:07.140000 --> 0:03:11.760000
 All right. All useful
 troubleshooting tips.

0:03:11.760000 --> 0:03:12.780000
 All right. So that's that.

0:03:12.780000 --> 0:03:15.320000
 So let's go ahead and continue
 my wiring here.

0:03:15.320000 --> 0:03:18.160000
 Let's see here. Let me get
 back to my whiteboard.

0:03:18.160000 --> 0:03:22.500000
 So now I want to connect 024 on
 switch 1 to 024 on switch 2.

0:03:22.500000 --> 0:03:28.080000
 And for that, I'm going to want
 to use this red crossover cable.

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 Okay. Just did that.

0:03:37.260000 --> 0:03:39.860000
 And sure enough, the lights are
 starting to come on right now.

0:03:39.860000 --> 0:03:41.940000
 And you can't see what I'm seeing.


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 But what happens is initially
 the lights go on.

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 There's sort of an amber
 or a brownish color.

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 And they stay that for a while.

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 And then they turn green.

0:03:51.200000 --> 0:03:54.140000
 So green means the switch port is wide
 open for sending and receiving

0:03:54.140000 --> 0:03:58.620000
 traffic. Amber or brown that happens first
 means it's actually going through

0:03:58.620000 --> 0:04:00.100000
 something called spanning tree.

0:04:00.100000 --> 0:04:02.580000
 And if you take my CCNA videos, you'll
 learn what spanning tree is.

0:04:02.580000 --> 0:04:05.640000
 That something is taught
 at the ICND2 level.

0:04:05.640000 --> 0:04:08.920000
 But spanning tree has to do some stuff
 first before it opens up the port

0:04:08.920000 --> 0:04:13.180000
 and the light turns green so
 it can actually be used.

0:04:13.180000 --> 0:04:16.460000
 Okay. So I did the switch
 1 to switch 2 connection.

0:04:16.460000 --> 0:04:18.780000
 Now let's just finish this off with
 the switch 2 to the router 1.

0:04:18.780000 --> 0:04:21.100000
 That's going to be
 a straight through.

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 Okay. So on switch 2, I'm going
 to take 0 slash 1 right there.

0:04:32.920000 --> 0:04:36.720000
 There we go. Okay.

0:04:36.720000 --> 0:04:39.520000
 And now to complete my,
 so that's building 1.

0:04:39.520000 --> 0:04:40.720000
 Building 1's done now.

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 Now to complete my cable, I'm going
 to do the stuff here in red.

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 So I need to connect
 my WAN cable now.

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 And for my WAN cable, that's where
 I'm going to use this funny looking

0:04:50.900000 --> 0:04:54.260000
 guy. Let me make this a little bit
 bigger here so you can see it.

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 So this is a serial cable.

0:04:57.320000 --> 0:04:59.720000
 And you can see it's got a special
 connection on the end of it.

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 And I think I have a bigger
 picture of it for you.

0:05:03.100000 --> 0:05:11.440000
 There we go. So the one I have is significantly
 shorter than that, but

0:05:11.440000 --> 0:05:13.520000
 it looks almost identical to that.


0:05:13.520000 --> 0:05:16.120000
 The ends of it look like this.

0:05:16.120000 --> 0:05:20.020000
 I honestly don't, I think this is called
 a DB60 connector because it has

0:05:20.020000 --> 0:05:23.580000
 something like 60 pins, but
 I don't quote me on that.

0:05:23.580000 --> 0:05:27.080000
 But when it comes to serial cables, there's
 all sorts of different connectors.

0:05:27.080000 --> 0:05:30.320000
 Basically the type you get is dependent
 on what are you connecting it

0:05:30.320000 --> 0:05:32.980000
 to, right? You need to connect, whatever
 you connect it to has to support

0:05:32.980000 --> 0:05:36.700000
 that type of connection.

0:05:36.700000 --> 0:05:44.460000
 And I don't know if you can really read
 it on here, but one into the cable,

0:05:44.460000 --> 0:05:55.200000
 this end right here, right
 here, it's written as DCE.

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 And this end right here
 is written as DTE.

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 And that's actually going to be important
 when it comes to the configuration

0:06:07.340000 --> 0:06:15.160000
 side. So I can plug either end of this
 into my routers, but I will have

0:06:15.160000 --> 0:06:17.120000
 to know which side is DCE.

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 And I'll tell you why
 in just a second.

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 So let's go ahead and make
 sure that the end is not.

0:06:20.840000 --> 0:06:25.120000
 And then go back to my diagram here
 and I'll plug router one to router

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 two. So looking at my picture,
 where is that?

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 Right here. So here's router one and
 router two, and I'm going to use

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 that special cable to connect
 from here to here.

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 So let me go ahead and do that.

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 Okay, I've just connected
 router one's port.

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 Now I'm going to connect
 router two.

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 Now serial connections are becoming
 a thing of the past.

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 These days, Ethernet,
 hold on a second.

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 These days, Ethernet is by far the
 most predominant technology.

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 So serial cables are becoming
 less and less popular.

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 But I've connected
 those two together.

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 Now it says slot one, but I don't necessarily
 know, like these over here,

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 these fast ether, it's clearly said,
 oh, that's fast ethernet zero slash

0:07:31.660000 --> 0:07:34.280000
 one or fast ethernet
 zero slash zero.

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 But I don't know if I'm going to configure
 this interface, and if I'm

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 going to label my diagram with the interface,
 I need to know exactly what

0:07:42.420000 --> 0:07:43.800000
 interface number that is.

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 Is it just serial one?

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 Is it serial one slash something?

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 So in order to do that, I'm going
 to get into the router.

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 Let's go to show session.

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 Do I already have a connection
 to the router?

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 Yes, connection number three.

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 And right now it's presenting me with what's
 called the initial configuration

0:08:11.340000 --> 0:08:16.300000
 dialogue, because I wiped out the configuration
 of this router before

0:08:16.300000 --> 0:08:19.160000
 this class to set it back
 to factory defaults.

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 And this is the dialogue that messes
 you get when you power up a router

0:08:22.780000 --> 0:08:25.520000
 or switch and it has
 no configuration.

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 So I do not want to go into the initial
 configuration dialogue because

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 that'll take me a million years to
 do just like three simple things.

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 Instead, I say no, I'll give it a chance
 here to do whatever it's going

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 to do. There we go.

0:08:47.780000 --> 0:08:51.500000
 And I can use that same command I showed
 you before, show IP interface

0:08:51.500000 --> 0:08:58.880000
 brief. And this particular case, now
 I know my serial, serial zero slash

0:08:58.880000 --> 0:09:03.900000
 one slash zero. So I'm going to
 label my diagram with that.

0:09:03.900000 --> 0:09:12.680000
 So this will be zero
 slash one slash zero.

0:09:12.680000 --> 0:09:16.520000
 Zero slash one slash zero.

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 And when I connected it in, router one
 has the end of the cable that was

0:09:25.560000 --> 0:09:30.520000
 labeled as DTE. Router
 two is labeled as DCE.

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 Why do I care? Why
 is that important?

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 The reason that's important is because
 remember what's going on on a cabling.

0:09:42.100000 --> 0:09:45.300000
 We have electrical signaling.

0:09:45.300000 --> 0:09:49.860000
 So we have different electrical
 pulses going off that cable.

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 And now I am not an electrical engineer,
 but let me sort of describe to

0:09:54.840000 --> 0:09:57.800000
 you the way it was just, I read something
 a long time ago that sort of

0:09:57.800000 --> 0:10:00.340000
 made an image in my head.

0:10:00.340000 --> 0:10:07.120000
 So think about you have two batteries
 in your hand, a little nine volt

0:10:07.120000 --> 0:10:11.240000
 battery and a car, an
 automotive battery.

0:10:11.240000 --> 0:10:14.900000
 You put the nine volt battery to your
 tongue, right, gives you a little

0:10:14.900000 --> 0:10:19.440000
 zap, right? You put that car battery
 to your tongue and it burns the hair

0:10:19.440000 --> 0:10:20.560000
 off of your head.

0:10:20.560000 --> 0:10:25.220000
 Both have electrical energy, but the
 quantity that that jolt that you

0:10:25.220000 --> 0:10:29.340000
 got was definitely different because
 the voltage is different.

0:10:29.340000 --> 0:10:35.240000
 Someone described the concepts
 of amps and volts to me.

0:10:35.240000 --> 0:10:37.680000
 Back a long time ago, I was literally
 like wondering what does that mean?

0:10:37.680000 --> 0:10:40.720000
 You know, amps and volts, because when
 it comes to electricity, you'll

0:10:40.720000 --> 0:10:43.600000
 see that. You know,
 120 volt outlet.

0:10:43.600000 --> 0:10:46.160000
 You know, three amps.

0:10:46.160000 --> 0:10:47.100000
 What does that mean?

0:10:47.100000 --> 0:10:49.520000
 Here's the way someone
 described it.

0:10:49.520000 --> 0:10:52.020000
 They said, think of
 it about this way.

0:10:52.020000 --> 0:10:55.420000
 Electricity running through a cable,
 what is it really happening?

0:10:55.420000 --> 0:10:57.580000
 It's electrons running through
 that cable, right?

0:10:57.580000 --> 0:11:01.520000
 So the electrons, the electrical, the
 negative charge of an atom, electrons

0:11:01.520000 --> 0:11:04.780000
 going through the copper
 in that cable.

0:11:04.780000 --> 0:11:06.580000
 That is your electricity.

0:11:06.580000 --> 0:11:12.160000
 So they said, imagine that instead
 of electricity, you had a hose with

0:11:12.160000 --> 0:11:19.220000
 water. And each electron is corresponding
 to a drop of water in that hose.

0:11:19.220000 --> 0:11:25.340000
 Okay? So if you had the water turned
 on, you put your hand up against

0:11:25.340000 --> 0:11:29.400000
 the end of that hose, you could measure
 how much pressure was coming out

0:11:29.400000 --> 0:11:32.780000
 of that hose. So that
 would be like volts.

0:11:32.780000 --> 0:11:36.200000
 The greater the volts, the
 greater the pressure.

0:11:36.200000 --> 0:11:40.000000
 So like if I turn up the hose, I've got
 more water going through and it's

0:11:40.000000 --> 0:11:42.600000
 putting more pressure
 against my hand.

0:11:42.600000 --> 0:11:48.160000
 So if I have a battery that's a nine volt
 battery and a hundred volt battery,

0:11:48.160000 --> 0:11:51.560000
 the nine volt battery, the electrons
 it's putting against my tongue are

0:11:51.560000 --> 0:11:53.360000
 very weak in pressure.

0:11:53.360000 --> 0:11:56.960000
 The hundred volt battery,
 much stronger in pressure.

0:11:56.960000 --> 0:12:00.040000
 Okay? This will make sense
 here in just a second.

0:12:00.040000 --> 0:12:05.380000
 Trust me. And then when it comes to
 amps, someone described it this way.

0:12:05.380000 --> 0:12:10.880000
 They said using that same concept of
 water in a hose, if I take a look

0:12:10.880000 --> 0:12:16.740000
 at like say one foot of that hose, I
 could measure how many water droplets

0:12:16.740000 --> 0:12:21.020000
 are passing through that one
 foot in like a second.

0:12:21.020000 --> 0:12:25.060000
 If I just have the water turned on, this
 is like a as a trickle, the water

0:12:25.060000 --> 0:12:28.560000
 droplets, there's not that many going
 through that one foot section of

0:12:28.560000 --> 0:12:30.760000
 hose in that period of time.

0:12:30.760000 --> 0:12:34.600000
 If I turn the water up, then there's
 more going through there in that

0:12:34.600000 --> 0:12:38.320000
 period of time. That's like
 amps in electricity.

0:12:38.320000 --> 0:12:42.540000
 If I take a amps, you know, the higher
 the amps means the more electrons

0:12:42.540000 --> 0:12:45.000000
 are being pushed through faster.

0:12:45.000000 --> 0:12:47.200000
 They're being pushed through
 more quickly through there.

0:12:47.200000 --> 0:12:49.660000
 Now like I said, I'm not an electrical
 engineer, but I've sort of used

0:12:49.660000 --> 0:12:52.420000
 this analogy to visualize
 things in the past.

0:12:52.420000 --> 0:12:59.300000
 And so how that relates to this is that
 all of these protocols like Ethernet,

0:12:59.300000 --> 0:13:04.320000
 they say we're going to break data
 down into electrical energy.

0:13:04.320000 --> 0:13:07.840000
 And the electrical energy is simply
 going to be represented as ones and

0:13:07.840000 --> 0:13:09.980000
 zeros. What does that mean?

0:13:09.980000 --> 0:13:15.240000
 That means if I'm sending the letter
 A across a wire, it's going to break

0:13:15.240000 --> 0:13:20.460000
 that A down into like say 1, 1, 0, 0, 0,
 and then it's going to use electrical

0:13:20.460000 --> 0:13:24.360000
 energy to represent those
 ones and those zeros.

0:13:24.360000 --> 0:13:26.280000
 So it might say, okay, here's
 what I'm going to do.

0:13:26.280000 --> 0:13:31.200000
 Ethernet might have a rule that says,
 well, to represent a 1, I'm going

0:13:31.200000 --> 0:13:35.320000
 to raise the voltage to a certain level,
 a certain pressure, and I'm going

0:13:35.320000 --> 0:13:38.500000
 to hold it for a certain amount
 of time and then let it go.

0:13:38.500000 --> 0:13:41.960000
 And when I'm transmitting a 0, I'm going
 to raise the voltage maybe just

0:13:41.960000 --> 0:13:46.700000
 to a different level and hold it for
 maybe a different amount of time

0:13:46.700000 --> 0:13:48.140000
 and then let it go.

0:13:48.140000 --> 0:13:51.940000
 So that's how electrical energy can
 be used to represent ones and zeros.

0:13:51.940000 --> 0:13:56.260000
 It's a variation of like the voltage,
 how much voltage you use and how

0:13:56.260000 --> 0:13:58.880000
 long you hold it before
 you let it go.

0:13:58.880000 --> 0:14:04.740000
 So when a nitcard like on my laptop sees
 voltage coming in, it says, okay,

0:14:04.740000 --> 0:14:08.880000
 number one, is that voltage coming
 in what Ethernet would define as a

0:14:08.880000 --> 0:14:12.580000
 1 or a 0? If the voltage is like this,
 it says, okay, that's not within

0:14:12.580000 --> 0:14:14.080000
 the scope of a 1 or a 0.

0:14:14.080000 --> 0:14:15.400000
 That's just electrical garbage.

0:14:15.400000 --> 0:14:18.140000
 But let's say the voltage comes
 in, it's like this much.

0:14:18.140000 --> 0:14:21.360000
 It says, okay, well, according to the
 rules of Ethernet, that much voltage

0:14:21.360000 --> 0:14:26.000000
 is a 1. And so, when look at that,
 it sees it go away and says, okay,

0:14:26.000000 --> 0:14:29.120000
 that was a 1. Now, voltage
 comes in like this.

0:14:29.120000 --> 0:14:32.560000
 Oh, according to Ethernet, that much
 voltage is a 0 and then that goes

0:14:32.560000 --> 0:14:34.260000
 away. All right.

0:14:34.260000 --> 0:14:39.980000
 So for that to happen, the network
 interface card on my laptop or on a

0:14:39.980000 --> 0:14:45.920000
 router or on a switch has to be monitoring
 that voltage as it comes in.

0:14:45.920000 --> 0:14:48.300000
 Because there's going to be periods
 of time when the voltage comes in

0:14:48.300000 --> 0:14:50.660000
 and there's going to be periods of time
 when it's let go and there's nothing.

0:14:50.660000 --> 0:14:53.480000
 It's just idle. There's
 nothing on that wire.

0:14:53.480000 --> 0:15:00.300000
 So it's sort of like, you know, you are
 waiting for a letter to be delivered.

0:15:00.300000 --> 0:15:04.860000
 And yet there's somebody in your neighborhood
 that is stealing your mail.

0:15:04.860000 --> 0:15:08.280000
 Okay. So you're going to want to, you're
 going to be looking out your

0:15:08.280000 --> 0:15:12.840000
 window periodically to see if the post
 office, if the mailman or mail

0:15:12.840000 --> 0:15:14.900000
 woman delivers, your letter.

0:15:14.900000 --> 0:15:18.680000
 And if you're looking at just the right
 time, you'll see that letter delivered

0:15:18.680000 --> 0:15:20.900000
 so you can run out
 there and grab it.

0:15:20.900000 --> 0:15:24.940000
 But if you've turned away from your
 window and you're in your kitchen,

0:15:24.940000 --> 0:15:29.640000
 the mailman could come, deliver the
 letter, the mailman could leave, the

0:15:29.640000 --> 0:15:31.540000
 thief could come steal
 that letter.

0:15:31.540000 --> 0:15:34.360000
 Now, when you look out there,
 the mailman is not there.

0:15:34.360000 --> 0:15:37.160000
 And if you check your post office
 box, there's nothing in it.

0:15:37.160000 --> 0:15:38.300000
 Same thing with a nit card.

0:15:38.300000 --> 0:15:43.560000
 A nit card, like billions of times per
 second, checks the wire and says,

0:15:43.560000 --> 0:15:45.280000
 okay, is there voltage
 coming in right now?

0:15:45.280000 --> 0:15:46.180000
 No, there's not.

0:15:46.180000 --> 0:15:47.140000
 Okay, I'll stop.

0:15:47.140000 --> 0:15:48.980000
 Let me check. Is there voltage
 coming in right now?

0:15:48.980000 --> 0:15:49.700000
 No, there's not.

0:15:49.700000 --> 0:15:51.320000
 I'll stop. So it's
 checking the wire.

0:15:51.320000 --> 0:15:55.620000
 It's scanning the wire for these
 pulses of electrical energy.

0:15:55.620000 --> 0:16:00.620000
 So what could happen is, is
 there something coming in?

0:16:00.620000 --> 0:16:01.520000
 No, there's not.

0:16:01.520000 --> 0:16:02.080000
 The wire's empty.

0:16:02.080000 --> 0:16:06.660000
 It looks away and in that microsecond
 or nanosecond that's looking away,

0:16:06.660000 --> 0:16:12.220000
 the voltage comes in as a one or a
 zero, drops, and then it looks and

0:16:12.220000 --> 0:16:17.020000
 it missed it. So in all these networking
 protocols, we have to have something

0:16:17.020000 --> 0:16:18.880000
 built in called clocking.

0:16:18.880000 --> 0:16:24.060000
 Clocking says, when I put the voltage
 on the wire as a one or a zero,

0:16:24.060000 --> 0:16:28.840000
 I want to make sure I do it in sync with
 when you are looking at the wire

0:16:28.840000 --> 0:16:32.440000
 so that you can see that
 voltage when it comes in.

0:16:32.440000 --> 0:16:37.640000
 Now, Ethernet, because Ethernet is a
 LAN protocol, it says, look, devices

0:16:37.640000 --> 0:16:39.560000
 are really close to each other.

0:16:39.560000 --> 0:16:43.740000
 So their clocking will be, if not
 identical, it'll be really close.

0:16:43.740000 --> 0:16:47.280000
 So Ethernet has a lot of built in protocols
 to make sure that voltage

0:16:47.280000 --> 0:16:50.900000
 levels aren't missed, that ones and
 zeros aren't missed, or if they are,

0:16:50.900000 --> 0:16:54.220000
 only a few of them at the front end
 are missed that aren't really that

0:16:54.220000 --> 0:16:56.000000
 critical anyway.

0:16:56.000000 --> 0:16:59.180000
 But when we're talking about a WAN connection,
 like this red connection

0:16:59.180000 --> 0:17:03.640000
 here where the devices could be miles
 apart from each other, clocking

0:17:03.640000 --> 0:17:05.000000
 becomes very important.

0:17:05.000000 --> 0:17:08.160000
 It becomes very important that when
 this guy puts a one or zero on the

0:17:08.160000 --> 0:17:12.860000
 wire, when it goes five or six or ten
 miles to this guy, he is looking

0:17:12.860000 --> 0:17:17.920000
 at the wire at the exact time when
 that pulse comes in so he can read

0:17:17.920000 --> 0:17:19.700000
 it and he can understand it.

0:17:19.700000 --> 0:17:24.640000
 So for that reason, on this type of a
 connection, on a serial connection,

0:17:24.640000 --> 0:17:27.280000
 one side provides a heartbeat.

0:17:27.280000 --> 0:17:30.840000
 One side provides this constant
 electrical heartbeat.

0:17:30.840000 --> 0:17:35.360000
 And the other side listens
 to that and locks onto it.

0:17:35.360000 --> 0:17:39.140000
 And now that they're synchronized with
 their clocking, they can both transmit,

0:17:39.140000 --> 0:17:42.260000
 they can both receive, and they don't
 have to worry about missing the

0:17:42.260000 --> 0:17:48.660000
 ones and zeros. That's where
 DCE and DTE come into play.

0:17:48.660000 --> 0:17:55.540000
 In a lab like this where I'm connecting
 two routers, right here, two routers

0:17:55.540000 --> 0:17:59.080000
 back to back with a serial cable.

0:17:59.080000 --> 0:18:00.960000
 This is my connection.

0:18:00.960000 --> 0:18:04.520000
 One of these interfaces is going to
 have to provide this clocking, this

0:18:04.520000 --> 0:18:07.180000
 heartbeat, because it's
 a serial interface.

0:18:07.180000 --> 0:18:10.480000
 It's expecting to connect to something
 really, really far away.

0:18:10.480000 --> 0:18:13.000000
 The other side is going
 to receive the clocking.

0:18:13.000000 --> 0:18:17.660000
 The DCE side is the one that
 provides the clocking.

0:18:17.660000 --> 0:18:19.640000
 There's actually going to be a command
 I'm going to type in called the

0:18:19.640000 --> 0:18:23.380000
 clock rate command
 on the DCE side.

0:18:23.380000 --> 0:18:27.000000
 That's why I said it was important for
 me to know which end of the cable

0:18:27.000000 --> 0:18:31.520000
 was labeled DCE versus DTE.

0:18:31.520000 --> 0:18:35.040000
 Now you might be wondering, well, what
 if I get into a network environment

0:18:35.040000 --> 0:18:38.740000
 where I'm not physically
 in front of the routers?

0:18:38.740000 --> 0:18:43.460000
 I know they're connected via serial,
 but I don't know which side is DCE

0:18:43.460000 --> 0:18:46.960000
 or DTE. I don't know which side needs
 the clocking command because I can't

0:18:46.960000 --> 0:18:50.960000
 see the cable. Well, there's a command
 you can issue to actually give

0:18:50.960000 --> 0:18:54.260000
 you that information.

0:18:54.260000 --> 0:19:04.040000
 Bring this up. So that command is show
 controllers and then you type in

0:19:04.040000 --> 0:19:05.940000
 your serial interface.

0:19:05.940000 --> 0:19:13.000000
 A lot of gobbley-gook in here, but what
 you're looking for, and I'll zoom

0:19:13.000000 --> 0:19:18.200000
 in on it here to make it a little bit
 bigger, is you're looking for this.

0:19:18.200000 --> 0:19:23.020000
 Right here about the
 third line down, DTE.

0:19:23.020000 --> 0:19:27.360000
 So I know that this router, I am not going
 to need the clock command because

0:19:27.360000 --> 0:19:29.620000
 that's the DTE side.

0:19:29.620000 --> 0:19:31.420000
 And that's router number one.

0:19:31.420000 --> 0:19:36.200000
 So it must be router number
 two that requires that.

0:19:36.200000 --> 0:19:45.600000
 Let's go ahead and look
 on router number two.

0:19:45.600000 --> 0:19:50.620000
 Alright, so show controller
 serial 010.

0:19:50.620000 --> 0:19:55.000000
 And here we see DCE.

0:19:55.000000 --> 0:19:57.500000
 So this side is going
 to need the clock.

0:19:57.500000 --> 0:20:00.080000
 So I'm just going to go into that interface
 right now, interface serial

0:20:00.080000 --> 0:20:05.420000
 010. And the command, I'll zoom
 in on it here so you can see it.

0:20:05.420000 --> 0:20:13.080000
 Clock rate. And if I use a question
 mark, you can see there's lots of

0:20:13.080000 --> 0:20:14.440000
 different rates.

0:20:14.440000 --> 0:20:19.920000
 My experience has been that if I select
 some of these upper rates here,

0:20:19.920000 --> 0:20:21.400000
 the interface flaps.

0:20:21.400000 --> 0:20:23.240000
 It goes like down up, down up.

0:20:23.240000 --> 0:20:24.400000
 I'm not sure why.

0:20:24.400000 --> 0:20:28.480000
 So I tried choosing something towards
 the higher end, but not at the very

0:20:28.480000 --> 0:20:30.800000
 high numbers. I'm not sure why it
 doesn't like the high number.

0:20:30.800000 --> 0:20:32.620000
 So I'm going to choose 800,000.

0:20:32.620000 --> 0:20:37.760000
 Now here's another
 way you could tell.

0:20:37.760000 --> 0:20:43.180000
 What if I had typed that command
 in the wrong router?

0:20:43.180000 --> 0:20:46.860000
 What if I had typed it in on the side
 that was DTE with the router blown

0:20:46.860000 --> 0:20:49.480000
 up and spit and shrapnel
 all over my face?

0:20:49.480000 --> 0:20:51.100000
 No, it wouldn't.

0:20:51.100000 --> 0:20:55.020000
 So let's go into router one.

0:20:55.020000 --> 0:20:58.740000
 Interface serial 010.

0:20:58.740000 --> 0:21:04.380000
 If I tried doing the command
 here, watch what happens.

0:21:04.380000 --> 0:21:09.840000
 It says up error only applies to DCE
 interfaces, so it didn't take the

0:21:09.840000 --> 0:21:19.320000
 command. All right, so I have now got
 a lot of my configuration done,

0:21:19.320000 --> 0:21:21.280000
 my cabling, I should say.

0:21:21.280000 --> 0:21:23.440000
 Now I just need to
 finish this off.

0:21:23.440000 --> 0:21:26.240000
 Router two to switch three.

0:21:26.240000 --> 0:21:27.860000
 So let's just do this here.

0:21:27.860000 --> 0:21:35.700000
 Let's say that on this side I'll have
 fast ethernet 0 slash 1 going to

0:21:35.700000 --> 0:21:46.520000
 0 slash 1 here. And here I will have
 0 slash 24 going to 0 slash 1 here.

0:21:46.520000 --> 0:21:57.320000
 All right, so let me find a couple
 more straight through cables.

0:21:57.320000 --> 0:22:01.440000
 And there's a question, who decides which
 side should be DCE or DTE, some

0:22:01.440000 --> 0:22:04.180000
 authority? It's just whoever
 made the cable.

0:22:04.180000 --> 0:22:08.540000
 The cable itself, one end was labeled
 as DCE, the other was labeled as

0:22:08.540000 --> 0:22:13.600000
 DTE, and the manufacturer of the
 cable just made it that way.

0:22:13.600000 --> 0:22:16.280000
 Like I said, I'm not electrical engineer,
 so I don't know if there's actually

0:22:16.280000 --> 0:22:19.680000
 a difference in the pinout
 or anything like that.

0:22:19.680000 --> 0:22:23.000000
 All right, so let's see here.

0:22:23.000000 --> 0:22:26.920000
 I want router two, 0 slash 1.

0:22:26.920000 --> 0:22:29.500000
 That's this guy right here.

0:22:29.500000 --> 0:22:33.260000
 And I want him connecting the
 0 slash 1 of switch three.

0:22:33.260000 --> 0:22:37.780000
 All right, I did that.

0:22:37.780000 --> 0:22:41.420000
 And lastly, one more straight
 through cable.

0:22:41.420000 --> 0:22:44.020000
 So we're running out of short ones here,
 so I'm going to use some of these

0:22:44.020000 --> 0:22:53.040000
 longer ones. And that's going to be
 the last interface on the switch.

0:22:53.040000 --> 0:22:57.040000
 Going to 0 slash 1 on the router.