sub secription jerimy ccna 200-101 switching - welcome to the world of switching.txt

8/11/2019 sub secription jerimy ccna 200-101 Switching - Welcome to the World of Switching.txt

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In the realm of networks you'll find there'sall kinds of devices out there, firewalls,

intrusion prevention system, NAS --

I mean there's all kinds of stuffthat can plug into a network.

However, there's two core devices that reallymake it work -- switches and routers --

both of which Cisco has staked their name on.

They will tell you, "We make the best

switch and router than money can buy,"

700:00:24,466 --> 00:00:26,766and I will tell you I absolutely agree.

800:00:26,906 --> 00:00:29,566It takes a lot of money, and it is the best.

900:00:29,566 --> 00:00:34,916So with that being said, switches is where most

people get their start into the Cisco world

1000:00:35,146 --> 00:00:40,496because they take a lot more normal dayto day stuff, normal day to day changes,

1100:00:40,496 --> 00:00:44,796as compared to routers that a lot of time youjust set up and forget about unless you are

1200:00:44,846 --> 00:00:47,546in a very dynamic and expanding organization.

1300:00:47,996 --> 00:00:51,006So switches are a lot of your day-to-day.

1400:00:51,006 --> 00:00:52,376So we'll start there, here.

15

00:00:52,826 --> 00:00:54,416We'll start there, here.


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1600:00:55,266 --> 00:00:56,166Did you get that?

1700:00:56,316 --> 00:01:00,206So we'll look at the different devices, kind of

the evolutions that switches have gone through.

1800:01:00,396 --> 00:01:02,696A big one for your understanding

1900:01:02,696 --> 00:01:05,686and certification purpose iscollision and broadcast domains.

20

00:01:05,686 --> 00:01:06,896And then I want to walk you

2100:01:06,896 --> 00:01:10,076through an end-to-end scenario,a day in the life of a switch.

2200:01:11,676 --> 00:01:17,276So the realm is 1980s' timeframe, Bengalsare singing Walk Like an Egyptian,

2300:01:17,276 --> 00:01:21,266big hair is the norm, and networkhubs are hitting the market.

2400:01:21,576 --> 00:01:25,90610 megabits per second speed isscreaming, this is life-changing events,

2500:01:25,906 --> 00:01:28,986where we now can have computers sharing data

2600:01:28,986 --> 00:01:32,396without people walking floppy disksback and forth down the aisles.

2700:01:32,396 --> 00:01:34,736I mean, that's the kind oftimeframe that we're in.

28

00:01:34,736 --> 00:01:38,776Ethernet is developing the standard of carriersense -- I should say it is developed --


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4100:02:31,396 --> 00:02:33,186That's where we have a collision.

4200:02:33,186 --> 00:02:39,436And that is collision detection, that's the

ability for the devices to be like, "Oh,

4300:02:39,436 --> 00:02:43,496we both sent at the same time,our data is scrambled, my bad."

4400:02:43,496 --> 00:02:48,816They run a back-off algorithm that they bothback off and then wait a certain amount of time

4500:02:48,816 --> 00:02:52,186to send again and then they both send andhope they don't collide a second time.

4600:02:52,516 --> 00:02:55,186Because collisions are really takingdown their network performance.

4700:02:55,186 --> 00:02:57,376And that was one of the things with token ring.

4800:02:57,516 --> 00:03:01,216Token ring said we're going to sendthis little ring around the network.

4900:03:01,376 --> 00:03:02,436I shouldn't say send a ring.

5000:03:02,436 --> 00:03:06,646Send this token around the networkthat all the computers are plugged into

5100:03:06,856 --> 00:03:10,476and only whoever has thetoken can send at a time.

5200:03:10,566 --> 00:03:13,926So this token is going bzz, bzz, bzz,you know, flying at the speed of light

5300:03:13,926 --> 00:03:17,736around this ring network, the devices


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are grabbing, adding their data.

5400:03:17,736 --> 00:03:19,456It never had a collision.

55

00:03:19,456 --> 00:03:22,336That was carrier sense multipleaccess collision avoidance,

5600:03:23,866 --> 00:03:25,896which you might say, "Well, that's gone," right?

5700:03:25,896 --> 00:03:26,936So token ring's gone.

5800:03:26,936 --> 00:03:30,886Well, yes, token ring is gone for the most part.

5900:03:30,986 --> 00:03:34,426However, collision avoidancehas reared its ugly head again.

6000:03:34,646 --> 00:03:35,776I shouldn't say ugly head.

6100:03:35,776 --> 00:03:37,696It's there in Wi-Fi.

6200:03:38,086 --> 00:03:42,916Wireless networks don't have the abilityto detect collisions, so they've gone back

6300:03:42,916 --> 00:03:46,906to a type of collision avoidancesystem, but that's a total other topic.

6400:03:46,906 --> 00:03:52,176So hubs are sitting here inEthernet running in such a sense

6500:03:52,176 --> 00:03:55,196that they have only one personable to send at a time.

66

00:03:55,196 --> 00:03:57,386Now, let me put a definition to that.


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6700:03:57,616 --> 00:04:01,316That is short for one-collision domain.

6800:04:02,796 --> 00:04:08,926Key topic to know: a hub, no matter how many

ports it has -- it could have, what is that,

6900:04:08,926 --> 00:04:14,026eight ports like I'm staring at,or 20 or 950,000 ports on a hub...

7000:04:14,026 --> 00:04:17,816it would not have that, but itwould all be one-collision domain

7100:04:17,956 --> 00:04:24,096which in rough English would just be howmany people can send or receive at a time.

7200:04:24,526 --> 00:04:26,916Now, I also want to emphasize the "or" there.

7300:04:27,706 --> 00:04:30,946"Or receive" means you arein a half-duplex world.

7400:04:31,266 --> 00:04:33,746Send or receive, so I'm prettymuch saying, "Well,

7500:04:33,746 --> 00:04:35,906I can send something or I can receive something.

7600:04:35,906 --> 00:04:36,706I cannot do both."

7700:04:36,706 --> 00:04:37,996It's like a walkie-talkie.

7800:04:38,616 --> 00:04:43,366Now, that was the world of the hub: oneperson sending or receiving at a time.

7900:04:43,606 --> 00:04:48,166

So the larger and larger your network group,the more and more collisions you would have


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8000:04:48,166 --> 00:04:51,776because there's more of a chance that people aresending and receiving, or sending or receiving,

8100:04:51,776 --> 00:04:55,706

at the same time and you're getting collisions,your network performance is going down.

8200:04:56,976 --> 00:05:04,606Likewise, you run into challenges with security,meaning a hub, if you bring up the OSI model.

8300:05:04,606 --> 00:05:06,736You know, you've got your seven layers,dut, dut, dut, dut, dut, dut, dut.

8400:05:06,956 --> 00:05:11,526Down here is the physical layer,which is where the hub resides.

8500:05:11,596 --> 00:05:14,936Physical layer devices haveno intelligence at all.

8600:05:15,276 --> 00:05:18,836

They receive electric signalsand they send electric signals,

8700:05:18,836 --> 00:05:20,216and that's exactly what this does.

8800:05:20,216 --> 00:05:25,176When this guy sends a packet -- let'ssay it's destined for this guy --

8900:05:25,416 --> 00:05:28,626what the hub does is receive it andsay, "Well, I just got some data.

9000:05:28,906 --> 00:05:32,006I'm going to send it outall of the network ports."

9100:05:32,786 --> 00:05:36,266This guy will get it, but so will

this guy, and so will this guy,

92


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00:05:36,476 --> 00:05:39,116and whatever other guys areattached to that network.

9300:05:39,116 --> 00:05:42,986Now, he's got the sad face because

his monitor is not a perfect square,

9400:05:43,176 --> 00:05:45,376but also because he is a hacker.

9500:05:45,736 --> 00:05:49,296He is using a program like Wire Shark.

9600:05:49,296 --> 00:05:53,676

It used to be called Ethereal,which you can freely download.

9700:05:53,676 --> 00:05:56,896It's like those programs we justtalked about in the Council Connection.

9800:05:56,976 --> 00:06:02,066You just type in Wire Shark in Google anddownload it, and what it will do is capture all

9900:06:02,066 --> 00:06:05,166of the data that it is receivingon that network port

10000:06:05,166 --> 00:06:08,646and store it so you can actually look at it.

10100:06:08,646 --> 00:06:12,756If you were good at Wire Shark, which ittakes a little training, but not much.

10200:06:13,446 --> 00:06:15,476Wait a sec, I've shown you Wire Shark.

10300:06:15,596 --> 00:06:16,286What am I talking about?

10400:06:16,286 --> 00:06:17,576You know what Wire Shark is all about.

10500:06:17,866 --> 00:06:21,616


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You can reassemble Excel spreadsheetsthat are being transferred.

10600:06:21,796 --> 00:06:26,686You can capture voice conversationsthat are happening, record phone calls

10700:06:26,686 --> 00:06:30,396that are being used by voice over --you can see emails that were being sent.

10800:06:30,396 --> 00:06:35,426I mean, everything is able to be seenbecause a hub sends everything everywhere.

109

00:06:35,426 --> 00:06:38,846So today -- that's enough abouthubs because they are network death.

11000:06:38,986 --> 00:06:44,556You do not or should not use thesein production because, number one,

11100:06:44,556 --> 00:06:49,046the collisions alone will slow your network toa crawl; and second off, the security, I mean,

11200:06:49,046 --> 00:06:51,706it's just, this is yesteryear technology.

11300:06:51,966 --> 00:06:55,366Also a hub maxed out at 100 megabits per second.

11400:06:55,416 --> 00:06:59,046Once it reached that speed, that's whereeverybody's like, "Okay, we've gone switching."

11500:06:59,046 --> 00:07:00,896You won't find a gigabit hub.

11600:07:01,836 --> 00:07:05,286So we move into the 1990s.

11700:07:05,286 --> 00:07:08,616The Bengals are now not singing

Walk Like an Egyptian.

118


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00:07:08,706 --> 00:07:11,476Actually, it's really funny.

11900:07:11,476 --> 00:07:14,936The Bengals performed at a Cisco live event.

12000:07:14,936 --> 00:07:18,176You know, Cisco's big, once-a-yearconference here in the United States.

12100:07:18,176 --> 00:07:24,836And they sang Walk Like anEgyptian and they forgot the words.

12200:07:24,836 --> 00:07:27,436

They got to like halfway throughand the girl was singing --

12300:07:27,436 --> 00:07:28,606you know, it's a really fast song.

12400:07:28,606 --> 00:07:31,676It's hard to keep up with and she's like,"I just totally," they forgot the words

125

00:07:31,676 --> 00:07:33,146to their own song and they made a joke about it.

12600:07:33,146 --> 00:07:34,316It was funny.

12700:07:34,316 --> 00:07:36,696Nonetheless, the Bengals areforgetting their own lyrics,

12800:07:36,776 --> 00:07:40,326we're coming out with network bridges in 1990s.

12900:07:40,326 --> 00:07:45,076The network bridges was this transitionarydevice between the hubs and switches

13000:07:45,386 --> 00:07:50,036which broke the network intomultiple-collision domains.

13100:07:50,316 --> 00:07:55,286


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Now, looking at it -- I couldn'tfind a picture of a network bridge.

13200:07:55,556 --> 00:08:00,946Looking at it you can't really tell much of adifference other than bridges had limited ports.

13300:08:00,946 --> 00:08:08,556You wouldn't find a 32- or 48- or 64-portbridge that you would plug your devices into.

13400:08:08,886 --> 00:08:12,086These were really expensive devicesthat you would have your hubs,

135

00:08:12,936 --> 00:08:17,886with all your devices attached, and as itstarted maxing out, like you're getting a lot

13600:08:17,886 --> 00:08:22,796of collision, you would introduce abridge which would have maybe two,

13700:08:22,796 --> 00:08:25,126maybe three, four different ports on it.

13800:08:25,126 --> 00:08:26,456And that bridge...

13900:08:28,606 --> 00:08:32,386would separate the multiple hub-based domains.

14000:08:32,386 --> 00:08:35,486Remember, over here, only oneperson can send at a time.

14100:08:35,486 --> 00:08:40,716So a bridge would, number one, introducemore than one-collision domains.

14200:08:40,986 --> 00:08:43,756Every port on a bridge is a collision domain.

14300:08:43,756 --> 00:08:47,156So over here we can have one

person sending or receiving.

144


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00:08:47,436 --> 00:08:50,896Over here we can have oneperson sending or receiving.

14500:08:50,896 --> 00:08:55,406So now we can have multiple people sending

or receiving at a time on the network,

14600:08:55,406 --> 00:09:00,536and the bridge is now introducing intelligence.

14700:09:00,606 --> 00:09:04,516OSI model, we're now moving up to layertwo, we're at the data link layer,

148

00:09:05,916 --> 00:09:10,806which is where this device resides,and it learned the MAC addresses.

14900:09:11,006 --> 00:09:14,946So the hub, we've got, we'll say, 10computers over here and 10 computers over here.

15000:09:15,046 --> 00:09:21,966This bridge, as the computers are sending andreceiving, it's learning which MAC addresses

15100:09:21,966 --> 00:09:25,376or which data link layer addressesare on each side of the network.

15200:09:25,376 --> 00:09:27,186So now you get some limited filtering.

15300:09:27,476 --> 00:09:32,416When somebody sends something that belongson, let's say, this side of the network.

15400:09:32,416 --> 00:09:33,256Let's say this guy sends.

15500:09:33,586 --> 00:09:34,326It hits the hub.

15600:09:34,326 --> 00:09:38,906

The hub sends it everywhere, includingthe bridge, and the bridge goes, "Oh,


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15700:09:39,056 --> 00:09:42,786well it looks like that was sent to thisMAC address," we'll call it MAC One.

15800:09:43,676 --> 00:09:45,986

"That was sent to this MAC address over here.

15900:09:46,256 --> 00:09:49,276So I'm not going to forward thaton to this side of the network.

16000:09:49,276 --> 00:09:49,886They don't need it."

161

00:09:51,006 --> 00:09:54,046So that's where our filtering came into play.

16200:09:54,046 --> 00:09:56,406So now, if you sent to theother side of the network --

16300:09:56,406 --> 00:10:00,326let's say we sent from the left side ofthe network here over to the right --

16400:10:00,326 --> 00:10:02,626as soon as it hits this hub, itexplodes and goes everywhere,

16500:10:02,626 --> 00:10:04,416so you're not really getting much filtering

16600:10:04,416 --> 00:10:07,186since we still have these layerone devices, but it was good.

16700:10:07,186 --> 00:10:09,226I mean, this was a good step.

16800:10:09,226 --> 00:10:12,196Now, here is the big Achillesheel of the bridges.

16900:10:12,606 --> 00:10:14,136

They were software-based.

170


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00:10:14,226 --> 00:10:17,796So these guys would slow down your network.

17100:10:17,856 --> 00:10:22,886When I first started teaching,I actually started with Novell

17200:10:23,186 --> 00:10:25,156and then moved into Microsoft technology.

17300:10:25,156 --> 00:10:29,346Talk about Windows serverMCSE certification back then.

17400:10:29,346 --> 00:10:34,376

And one of the things, I still remember this forsome reason, I was talking about how Windows,

17500:10:34,376 --> 00:10:37,876Windows 2000 I think it was, could do RAID.

17600:10:38,116 --> 00:10:41,096Meaning it could do RAIDlevel one or RAID level five,

177

00:10:41,096 --> 00:10:43,746which is mirroring two hard drives together.

17800:10:43,746 --> 00:10:46,376And I had a guy in class go "Ah, ha, ha, yeah...

17900:10:46,576 --> 00:10:50,046like I would do that with Windows."

18000:10:50,046 --> 00:10:51,186And back then I didn't know better.

18100:10:51,186 --> 00:10:53,496I was like, "Well, why wouldn'tyou do that with Windows?"

18200:10:53,496 --> 00:10:54,316He says, "No, no, no.

183

00:10:54,486 --> 00:10:56,486We buy separate hardware to do that.


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18400:10:56,486 --> 00:10:59,466We buy RAID controller cards,"which are now common everywhere.

18500:10:59,716 --> 00:11:02,356

RAID controller cards that offload that,

18600:11:02,356 --> 00:11:04,736so Windows doesn't have toworry about mirroring those.

18700:11:04,736 --> 00:11:09,996Well, in the same sense, Windows would slow downa lot if you actually tried to do RAID with it

18800:11:09,996 --> 00:11:12,246because it's having to keepup with hard drive functions.

18900:11:12,246 --> 00:11:13,226Same thing here.

19000:11:13,226 --> 00:11:17,536The bridge is learning all theseMAC addresses in the software.

19100:11:17,536 --> 00:11:22,106It's processing them in the software, soas stuff goes from one side of the network

19200:11:22,106 --> 00:11:26,796to the other, it slows down because of theprocessing that's taking place on that device.

19300:11:28,136 --> 00:11:31,936And now we make the turninto the new millennium.

19400:11:31,936 --> 00:11:36,316Around year 2000, you start seeing networkswitches becoming a commonplace thing.

19500:11:36,506 --> 00:11:37,316And it's funny.

19600:11:37,316 --> 00:11:39,606I'm thinking "Okay, we had


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the '80s with the Bengals.

19700:11:39,606 --> 00:11:43,876What do you say happened aroundthe turn of the generation?"

19800:11:43,876 --> 00:11:45,436You know, it's like the Y2K scare.

19900:11:45,436 --> 00:11:46,616Well, that's an event.

20000:11:46,616 --> 00:11:49,386There's nothing that really characterizesthings that have happened, you know,

20100:11:49,596 --> 00:11:55,366maybe the dissolution of normal relationshipsto where now everybody communicates via texting

20200:11:55,366 --> 00:11:58,066and Facebook and no longerface-to-face because that's weird

20300:11:58,166 --> 00:12:02,126

to actually see somebody and talk to them.

20400:12:02,126 --> 00:12:05,236I'm saying that's weird tohave natural relationships.

20500:12:05,236 --> 00:12:07,796Here I am talking to myselfstaring at a screen, yeah.

20600:12:08,046 --> 00:12:09,636I'm a lot better, right?

20700:12:09,636 --> 00:12:12,496So anyway, here we are in this switching world.

20800:12:12,496 --> 00:12:15,256Every port now has its owncollision, and you know what?

20900:12:15,256 --> 00:12:17,066Let me actually move this to the top.


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21000:12:17,596 --> 00:12:23,076Because everything that I said about bridgesis the same when it comes to switches; however,

211

00:12:23,246 --> 00:12:25,646we now have a very high port density.

21200:12:25,716 --> 00:12:27,666Like a lot of devices can plug into these.

21300:12:27,666 --> 00:12:30,106We're no longer limited totwo or three or four ports.

21400:12:30,106 --> 00:12:34,156But the biggest thing thatchanged was the creation of ASICs.

21500:12:34,596 --> 00:12:35,366What are those?

21600:12:35,826 --> 00:12:39,536Application-specific integrated circuitry.

21700:12:39,966 --> 00:12:45,146Such a huge concept for ournetwork devices, because this moved

21800:12:45,516 --> 00:12:49,586that software-based processingof the bridge into the hardware.

21900:12:49,836 --> 00:12:52,396And you're going to see this topiccome up again and again and again.

22000:12:52,766 --> 00:12:55,256All ASICs are is somebody engineered a chip.

22100:12:55,376 --> 00:12:59,276Here's my little chip, a little chip with wiresand connections and all that kind of stuff

222

00:12:59,276 --> 00:13:04,246to where in the hardware the intelligenceof the device, it's able to handle it


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22300:13:04,246 --> 00:13:06,026without relying on any kind of software.

22400:13:06,026 --> 00:13:12,146

And any time you introduce ASICs intothe picture, you introduce a lot of speed

22500:13:12,146 --> 00:13:14,976because you have it all beingprocessed in hardware.

22600:13:15,216 --> 00:13:16,866No longer does the softwarehave to get involved.

22700:13:16,866 --> 00:13:21,086ASICS has changed the world ofswitching or bridging, I should say,

22800:13:21,086 --> 00:13:22,786to where now switching is commonplace.

22900:13:22,786 --> 00:13:25,146ASICs changed the world of VPNs.

23000:13:25,816 --> 00:13:29,426We would no longer be able toscale virtual private networks,

23100:13:29,426 --> 00:13:33,816which is encrypted tunnels running acrossthe internet, if we didn't have these ASICs,

23200:13:33,816 --> 00:13:35,966these chips that handle a lot of the encryption,

23300:13:35,966 --> 00:13:39,396because the encryption alone wouldbury the software of the device.

23400:13:39,816 --> 00:13:43,456So ASICS are a world-changing event.

235

00:13:43,456 --> 00:13:47,176They cause a lot of thesedevices to just move a lot faster.


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23600:13:47,176 --> 00:13:54,556Now we have switches where it's able to moveas fast as the hubs were, which is wire speed.

237

00:13:54,556 --> 00:13:58,506As electric signals are coming in,it's processing and sending them out.

23800:13:58,506 --> 00:14:01,226Every port on a switch isits own collision domain.

23900:14:01,606 --> 00:14:06,556So when you come to a switch, you

look at how many ports there are.

24000:14:06,556 --> 00:14:09,806Let's say it's a 24-port switchor this one looks like a 20...

24100:14:09,966 --> 00:14:12,836they got these two weird ports,so maybe a 26-port switch,

242

00:14:12,836 --> 00:14:15,816so you've got 26-collision domains.

24300:14:15,926 --> 00:14:21,976And again, going back to our simple definition,26 people, 26 devices plugged in there can send

24400:14:22,456 --> 00:14:26,926and -- ooh, there's a big change-- and receive at the same time.

24500:14:27,276 --> 00:14:31,806We've gone full duplex to where now insteadof a walkie-talkie, you're like a telephone

24600:14:31,806 --> 00:14:34,836to where both people can talk on topof each other and still understand,

24700:14:34,836 --> 00:14:37,416

at least in the computer world,still understand each other.


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24800:14:37,416 --> 00:14:44,006So when you say this is a 100-megabit persecond switch, or 100-megabit per second port,

24900:14:44,216 --> 00:14:48,326

really you're getting 200 megabits persecond if you're running it at full duplex

25000:14:48,326 --> 00:14:54,166because you get 100 send and 100 receivethat you can do at the same time.

25100:14:54,166 --> 00:14:59,746Now, all network speeds are rated athalf duplex, so when you see a gigabit-

25200:14:59,746 --> 00:15:04,986or a 100-megabit per second port, it'sbeing rated at half duplex, so I mean,

25300:15:04,986 --> 00:15:07,446you truly can never go above that speed.

25400:15:07,606 --> 00:15:09,806It's just now you can do send

and receive at the same time.

25500:15:09,806 --> 00:15:12,126Totally kind of life-changing event there.

25600:15:12,416 --> 00:15:14,296You also support varying port speeds.

25700:15:14,296 --> 00:15:17,726A hub had to have all the same speed.

25800:15:17,926 --> 00:15:22,936If it was a 10-megabit per second port, everyport on that hub, a 10-megabit per second hub,

25900:15:22,936 --> 00:15:24,906every port on the hub wouldbe 10-megabits per second.

260

00:15:24,906 --> 00:15:28,196But with switches you could have, forinstance, these guys, and this is common,


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26100:15:28,436 --> 00:15:34,696over on the left being 100-megabit persecond connection and these two guys

262

00:15:34,696 --> 00:15:40,456over on the right might be 1,000 megabits persecond or a gigabit, or as technology continues

26300:15:40,456 --> 00:15:43,106to evolve, we're going tosee these being common,

26400:15:43,296 --> 00:15:49,1761,000-megabit per second ports is

normal customer plug-ins and normal use

26500:15:49,176 --> 00:15:53,866and then maybe these uplinks are10,000 megabits per second, or 10 gig,

26600:15:53,866 --> 00:15:59,526or now 40,000 megabits per second or 40gigabits per second uplinks that you can have.

267

00:15:59,526 --> 00:16:04,806So that way you can have switches that aredaisy-chained together to where, you know,

26800:16:04,806 --> 00:16:08,096you've got all these guys thatare all 100 and this is 1,000,

26900:16:08,096 --> 00:16:11,946so that way this doesn't become a bottleneckand all these guys are 100 and this is 1,000,

27000:16:11,946 --> 00:16:17,076so that way you can link these togetherwithout bottlenecking them on these speeds.

27100:16:17,226 --> 00:16:22,916These switches are managed and intelligentto where -- and I'll flip that term.

272

00:16:22,916 --> 00:16:25,696They're intelligent in the sensethat they have the same capabilities


22/45

27300:16:25,696 --> 00:16:28,306of the bridge to learn MAC addresses.

27400:16:28,306 --> 00:16:32,836

So as these switches power on, they will learnall the different devices that are on there.

27500:16:32,836 --> 00:16:40,296So now when this guy sends a packet into theswitch, it will be able to send it out to just

27600:16:40,296 --> 00:16:43,476that guy because he knowswhere the MAC address is at.

27700:16:44,056 --> 00:16:45,256He's located all of it.

27800:16:45,256 --> 00:16:48,536He will even learn, for instance, ifyou start daisy-chaining them like this,

27900:16:48,536 --> 00:16:51,876you've got 20 MAC addresses down

here, we'll say, that it's learned.

28000:16:51,876 --> 00:16:56,526This switch will learn that all 20 of thoseMAC addresses are accessible on this one port.

28100:16:57,556 --> 00:17:02,066So it's not uncommon to see one port with20 MAC addresses, which tells you, "Okay,

28200:17:02,066 --> 00:17:04,396that port must be daisy-chainedto another device

28300:17:04,396 --> 00:17:07,226that has all kinds of devices plugged into it."

28400:17:07,226 --> 00:17:10,656So that's the intelligent side.

28500:17:10,876 --> 00:17:13,966The managed side is going to be


23/45

what we get into with the Cisco iOS.

28600:17:13,966 --> 00:17:16,476We can do things with our switches.

287

00:17:16,596 --> 00:17:17,646We can change things.

28800:17:17,646 --> 00:17:18,886We can modify settings.

28900:17:18,886 --> 00:17:20,436We can add features.

290

00:17:20,436 --> 00:17:24,456Now, one of the nice things about Ciscoswitches, out of the box, they work.

29100:17:24,926 --> 00:17:26,016That's great.

29200:17:26,156 --> 00:17:29,266You plug them in, you plug in yourcomputers, and it's working like a switch,

29300:17:29,496 --> 00:17:34,106but you're only getting limitedfeature set by doing that.

29400:17:34,106 --> 00:17:35,606You're just getting the base functionality.

29500:17:35,606 --> 00:17:41,606You might as well go buy some other brandor what you'll hear is an unmanaged switch,

29600:17:41,606 --> 00:17:43,426with doesn't really have the iOS.

29700:17:43,426 --> 00:17:44,836It doesn't have features.

29800:17:44,836 --> 00:17:47,996You just plug it in and plug stuff

together and it just kind of works.

299


24/45

00:17:47,996 --> 00:17:51,286It learns MAC addresses and does its thing.

30000:17:51,286 --> 00:17:53,846Cisco adds features that you can configure.

30100:17:53,846 --> 00:17:56,526That's going to be what we talkabout in the switching world today.

30200:17:56,856 --> 00:18:00,516Now, I know you're looking at, I was justthinking of what else about these things?

30300:18:00,546 --> 00:18:04,516

They smell good and they're smooth-- now, I'm only half joking.

30400:18:04,516 --> 00:18:07,976When you open, if you have theprivilege of opening a Cisco switch,

30500:18:07,976 --> 00:18:10,386it has that new cellophane smell.

306

00:18:10,466 --> 00:18:13,256It only lasts for about 10 secondsafter you pull it out of the box.

30700:18:13,526 --> 00:18:14,326It's so good.

30800:18:14,416 --> 00:18:17,436After you've opened a number of thesedevices, you know, initially it's like "Ooh,

30900:18:17,436 --> 00:18:21,576that's repulsive," but after a little whileyou're like, "Man, I just, I love that."

31000:18:21,576 --> 00:18:24,726It's like Pavlov's dogs, youknow, you kind of jingle the bell.

31100:18:24,936 --> 00:18:27,966

Like when I smell that cellophaneI'm like, "Ooh, new Cisco device.


25/45

31200:18:27,966 --> 00:18:29,086Where is it?"

31300:18:29,346 --> 00:18:31,926So it smells good and it is smooth to touch.

31400:18:31,926 --> 00:18:35,926It is. You install these into racks -- you know,I'm kind of tongue-in-cheek on saying that.

31500:18:36,186 --> 00:18:40,776But this is the core of what ournetworks use to connect devices.

316

00:18:42,356 --> 00:18:46,526One more piece that I want to add onhere, because it was on the title slide,

31700:18:46,526 --> 00:18:50,006I didn't add it in my bullets, isthe concept of a broadcast domain.

31800:18:51,256 --> 00:18:54,916A broadcast domain essentially means,

31900:18:54,916 --> 00:19:00,116how far will a broadcast messagego before it's stopped, okay?

32000:19:00,116 --> 00:19:03,906So a broadcast, broadcasts justhappen in the network world.

32100:19:03,906 --> 00:19:05,596They're partially how computers work.

32200:19:05,806 --> 00:19:10,966Like when this computer boots up, if it'susing DHCP, it doesn't have an IP address,

32300:19:11,016 --> 00:19:14,976so it will send a broadcast messagesaying, "Hello, anybody out there?

324

00:19:15,116 --> 00:19:18,716I don't have an address,"an IP address, I should say,


26/45

32500:19:18,716 --> 00:19:20,946"but if somebody could giveme one that would be great."

326

00:19:21,326 --> 00:19:22,986It's looking for a DHCP server.

32700:19:23,356 --> 00:19:28,956Now, on a switch, just like a hub,broadcasts will go to all ports.

32800:19:29,416 --> 00:19:31,376That's one of our scalability concerns.

32900:19:31,376 --> 00:19:34,426A hub you can only scale toa few devices, I mean, 30,

33000:19:34,426 --> 00:19:36,94640 devices you're startingto really hit the max.

33100:19:37,196 --> 00:19:39,956Switches you can get into

the hundreds of devices.

33200:19:40,126 --> 00:19:45,496You know, 200, 300, 400 devices, but eventuallyyou're going to reach a point where you get

33300:19:45,496 --> 00:19:48,396so many broadcasts becauseeverybody's kind of chitter-chattering

33400:19:48,396 --> 00:19:51,616around that you're impacting yourcomputer and network performance.

33500:19:51,616 --> 00:19:55,166So you start dividing it upinto more broadcast domains,

33600:19:55,166 --> 00:19:58,006and we'll talk about how that's possible, but

I just wanted to throw that term out there

337


27/45


28/45

00:20:48,226 --> 00:20:51,816so once you exceed that,now you're kind of stuck.

35100:20:51,816 --> 00:20:54,776So a lot of people will start

going with things like fiber.

35200:20:54,776 --> 00:20:57,566You know, a lot of times there'll bebuildings across the street from each other;

35300:20:57,566 --> 00:21:01,996they need to run cables that are longer than100 meters or just a really big building,

35400:21:01,996 --> 00:21:04,476so they'll start putting fiber in here.

35500:21:04,476 --> 00:21:07,526This is actually known as an SFP module.

35600:21:07,676 --> 00:21:09,816It's a fiber-optic modulethat you can slide in there.

35700:21:09,926 --> 00:21:10,976You buy them separately.

35800:21:12,006 --> 00:21:15,206I think SFP stands for "small form factor..."

35900:21:17,706 --> 00:21:19,536pluggable.

36000:21:20,476 --> 00:21:24,216I had to pause and look it up.

36100:21:24,406 --> 00:21:25,776Everybody just says SFP.

36200:21:25,916 --> 00:21:28,396For some reason the acronymisn't used very often.

36300:21:28,396 --> 00:21:30,626But this has a fiber-optic connection.


29/45


30/45

37600:22:24,496 --> 00:22:27,686where you have four slotswhere you can plug in SFPs.

37700:22:27,686 --> 00:22:30,196

Now you might say, "Why doyou have them changeable?"

37800:22:30,356 --> 00:22:32,376Well, there's different kindsof fiber you can get.

37900:22:32,376 --> 00:22:36,316There's multi-mode fiber, whichis really easy to work with

38000:22:36,316 --> 00:22:39,176and a lot cheaper to make because it's plastic.

38100:22:39,176 --> 00:22:43,966And so multi-mode fiber has the ability ofbeing really easy to work with and really cheap,

38200:22:44,146 --> 00:22:46,846but it doesn't go as far as single-mode fiber.

38300:22:47,136 --> 00:22:51,486And single-mode fiber is always glassthat, you know, if you were to open this

38400:22:51,486 --> 00:22:55,236up with a little razor, you would seereally, really thin glass that it's using

38500:22:55,426 --> 00:22:57,626and a lot more difficult to workwith and a lot more expensive.

38600:22:57,626 --> 00:23:02,406So based on what your needs are, you can buysingle-mode or multi-mode fiber interfaces

38700:23:02,406 --> 00:23:04,816and then you just have to -- you've justgot to make sure they're compatible.

38800:23:04,816 --> 00:23:07,676


31/45


32/45

00:23:51,876 --> 00:23:54,726So let's say, now we've seen our MAC addresses.

40200:23:54,726 --> 00:23:59,356MAC addresses are 12 characters, so let'sjust say this happy computer right here is 11;

40300:23:59,356 --> 00:24:04,9661;11;11;11;11.

40400:24:05,086 --> 00:24:06,186You'll see them written this way.

40500:24:06,536 --> 00:24:08,536That's a common way to write a MAC address.

40600:24:08,536 --> 00:24:09,886You'll also see them written this way.

40700:24:09,886 --> 00:24:16,336This is a lot of times what you'll see inthe Cisco world: 2222:2222 or Microsoft a lot

40800:24:16,336 --> 00:24:21,696of times, like if you open a

command prompt and do an IP config,

40900:24:23,496 --> 00:24:25,846all -- Microsoft likes using dashes.

41000:24:26,066 --> 00:24:28,876So, for instance, it'll showyou MAC addresses like this.

41100:24:29,306 --> 00:24:32,986So I'll make this guy, let's just useall three styles here on the screen.

41200:24:32,986 --> 00:24:40,41633;33;33;33;33;33, so reallythe style doesn't matter so much

41300:24:40,416 --> 00:24:42,736as that there's 12 characters inside of it.

41400:24:42,736 --> 00:24:45,336So every MAC address is 12 characters long.


33/45

41500:24:45,336 --> 00:24:50,346So this guy, let's say the guy on theleft, the happy computer is talking

416

00:24:50,346 --> 00:24:52,446to the straight-faced computer in the middle.

41700:24:53,036 --> 00:24:57,066So he's going to send a frame,let's just say I ping...

41800:24:57,526 --> 00:25:03,486let's see, I'm trying to thinkof how far back I'll go here.

41900:25:03,486 --> 00:25:08,786Okay. So let's just say IPaddress-wise, this guy is 10.1.1.1;

42000:25:08,986 --> 00:25:11,636this guy is 10.1.1.2 on an IP address.

42100:25:11,636 --> 00:25:17,026So on this computer I type

in ping 10.1.1.2, right?

42200:25:17,316 --> 00:25:21,466What's the first messagethat's going to be sent?

42300:25:21,466 --> 00:25:24,096An ARP -- address resolution protocol --

42400:25:24,096 --> 00:25:28,826saying, "Okay, great, I see that you're pinging10.1.1.2, but I've got to create a frame.

42500:25:28,826 --> 00:25:32,666I've got to have source and destination IPaddresses, source and destination MAC address.

42600:25:32,706 --> 00:25:38,026I don't have the MAC address for10.1.1.2," so ARP is a broadcast message.

42700:25:38,116 --> 00:25:40,276


34/45

So it's going to say, "Hello, network.

42800:25:40,276 --> 00:25:42,836Who is 10.1.1.2?"

429

00:25:42,836 --> 00:25:43,826So that hits the switch.

43000:25:43,826 --> 00:25:48,266Now this is, both of these switches arenow considered one broadcast domain.

43100:25:50,116 --> 00:25:55,656So it's going to receive that broadcast andsend it out to all ports that are active.

43200:25:55,656 --> 00:25:58,226I mean, there's nothing pluggedin, so this guy gets the broadcast,

43300:25:58,226 --> 00:25:59,616this guy, it shoots across to fiber.

43400:25:59,616 --> 00:26:02,376These two get the broadcast

saying, "Who is 10.1.1.2?"

43500:26:02,376 --> 00:26:05,196Now, this is the only onethat will respond to that one,

43600:26:05,196 --> 00:26:08,146so the straight-faced computercomes back and says "Oh, that's me."

43700:26:08,446 --> 00:26:11,896So -- and I jumped a little ahead.

43800:26:12,036 --> 00:26:13,066He goes, "Oh, that's me.

43900:26:13,206 --> 00:26:15,896I am 10.1.1.2; this is my MAC address."

440

00:26:15,896 --> 00:26:17,736But let me take a step back.


35/45

44100:26:17,736 --> 00:26:22,776As soon as this broadcast came into theswitch, I mean, if we were to grab that

44200:26:22,776 --> 00:26:26,016

and use Wire Shark and look at it, wewould say, "Okay, it's an ARP message.

44300:26:26,016 --> 00:26:27,336It's trying to find a MAC address.

44400:26:27,336 --> 00:26:32,256It's coming from the sourceIP address of 10.1.1.1.

44500:26:32,506 --> 00:26:36,576It's looking for the destinationIP address of 10.1.1.2.

44600:26:36,576 --> 00:26:42,436It's coming from the source MAC addressof 11;11, you know, this guy right here.

44700:26:42,796 --> 00:26:47,376And it's going to the destination

MAC address of, I don't know.

44800:26:47,626 --> 00:26:51,296Now, you might say, "Well, wait asecond; it doesn't know this MAC address.

44900:26:51,296 --> 00:26:52,286It has to have something in there."

45000:26:52,536 --> 00:26:53,776Well, it absolutely does.

45100:26:54,146 --> 00:26:56,536It's destination MAC address is FFFFFF.

45200:26:56,536 --> 00:27:02,606Remember, MAC addresses are hexadecimal,so A through F are valid characters.

453

00:27:02,606 --> 00:27:08,406And the very, very last possible MAC addressin all the scheme, FFFFFF, means a broadcast.


36/45

45400:27:08,746 --> 00:27:09,436That's what that means.

45500:27:09,436 --> 00:27:13,516

So the switch receives it destined tothis MAC address that it will never learn

45600:27:13,516 --> 00:27:18,736on any individual port and it says, "Okay,well, that MAC address, it says go everywhere.

45700:27:18,736 --> 00:27:20,466But I just learned something."

45800:27:21,276 --> 00:27:25,996By seeing this broadcast message come intothe switch it goes, "Oh, oh, oh, wait a sec.

45900:27:26,126 --> 00:27:30,056On port -- " let's just say this is port 0/2.

46000:27:30,056 --> 00:27:31,946You know, this one up here was 0/1.

46100:27:31,946 --> 00:27:39,166So it says "Okay, 0/2 is really 1111:1111:1111."

46200:27:39,166 --> 00:27:43,426So now the switch has becomeone MAC address smarter.

46300:27:44,646 --> 00:27:50,516Now this guy comes back and says, "Oh,that's me, let me send my ARP reply."

46400:27:50,516 --> 00:27:52,156Here's his ARP message.

46500:27:52,156 --> 00:27:55,476"I'm coming from the source IPaddress going to this destination,

46600:27:55,686 --> 00:27:59,386

coming from this source MACaddress, going to this destination."


37/45

46700:27:59,386 --> 00:28:00,706Let me just zoom in on that.

46800:28:00,706 --> 00:28:01,886You know if I were to break that packet down,

46900:28:01,886 --> 00:28:05,216it would say the destinationMAC address is the ones.

47000:28:05,216 --> 00:28:08,986The source MAC address is thetwos and it will come into switch.

471

00:28:08,986 --> 00:28:10,446Now, two things happen here.

47200:28:11,086 --> 00:28:13,296One is, let's say the switch is looking at,

47300:28:13,296 --> 00:28:17,676let's just say that is port0/12, or let's say 0/11.

474

00:28:17,796 --> 00:28:20,636I'm trying to be accurate looking at the switch.

47500:28:20,636 --> 00:28:21,646Let's say 0/15.

47600:28:21,646 --> 00:28:24,766So it's going to say, "Okay, Ijust learned another MAC address

47700:28:24,766 --> 00:28:26,106because I just saw a frame come in there.

47800:28:26,106 --> 00:28:28,006It is 2222.

47900:28:28,396 --> 00:28:33,016So I now know that that computeris available on port 0/15."

48000:28:33,016 --> 00:28:34,096Now, this is all in the CAM.


38/45

48100:28:34,096 --> 00:28:39,766All in the memory of the switch, so if Ipull the plug on this switch at any time,

482

00:28:39,946 --> 00:28:43,656all of this goes away and it has torelearn all of these MAC addresses.

48300:28:43,656 --> 00:28:47,606So that's the first thing it does is itlearns that MAC address is on that port.

48400:28:47,606 --> 00:28:49,566But now it's become smarter.

48500:28:50,056 --> 00:28:52,456It goes, "Oh, it looks like you'retrying to go to the destination

48600:28:52,456 --> 00:28:55,786of 111111, you know, all the ones.

48700:28:55,786 --> 00:28:56,626I know where that guy is.

48800:28:56,726 --> 00:28:58,016He's on port 0/2."

48900:28:58,016 --> 00:29:02,966So now instead of sending the reply to allports, the switch is just going to say, "Okay,

49000:29:02,966 --> 00:29:08,706let me switch you right over here down tothis device" and only those two get it.

49100:29:08,706 --> 00:29:12,726And now point-to-point communicationcan happen between those guys

49200:29:12,726 --> 00:29:16,896without disturbing anybody else becausethe switch has learned their MAC address.

49300:29:17,206 --> 00:29:19,406Now, let's talk of real world.


39/45

49400:29:19,546 --> 00:29:20,856Okay, a switch powers on.

49500:29:21,156 --> 00:29:26,496

How long is it going to take beforeit learns all of the MAC addresses

49600:29:26,496 --> 00:29:28,146on the network, or the ones that it needs?

49700:29:28,766 --> 00:29:31,396I would say five to 10 seconds.

498

00:29:31,896 --> 00:29:34,266I know. Really, that fast?

49900:29:34,266 --> 00:29:38,056Yeah. I mean hundreds of devices it canlearn in five to 10 seconds because all

50000:29:38,056 --> 00:29:41,356of these guys are talking, and if you'retalking about powering on a switch, well,

50100:29:41,466 --> 00:29:45,116as that switch is powering on, the devicesare chatting They need IP addresses.

50200:29:45,116 --> 00:29:46,036They want to communicate.

50300:29:46,036 --> 00:29:51,416So the switch is gaining knowledge essentiallyright after it boots and is ready to do that.

50400:29:51,416 --> 00:29:54,976It's ready to go, so it does not takelong for these guys to learn at all.

50500:29:55,516 --> 00:30:01,646Also keep in mind these entrieshave a life span of five minutes,

506

00:30:02,446 --> 00:30:06,436meaning if the device goesquiet for five minutes --


40/45

50700:30:06,436 --> 00:30:11,576and this is by default, you can change it -- theswitch will forget where that MAC address is.

508

00:30:11,906 --> 00:30:13,796So this guy goes quiet.

50900:30:13,936 --> 00:30:15,446He disappears from the table.

51000:30:15,446 --> 00:30:16,276Now, no big deal.

511

00:30:16,276 --> 00:30:20,536That just means the next time somebody has tocommunicate with him, the switch will treat it

51200:30:20,536 --> 00:30:25,716like a broadcast, because it's goingto say, "I don't know where 111111 is."

51300:30:25,716 --> 00:30:28,086So it will send it everywhereand then relearn that.

51400:30:28,086 --> 00:30:30,796The reason it does that isbecause MAC addresses can change.

51500:30:30,796 --> 00:30:33,756Now, it's rare, really rarefor a MAC address to change.

51600:30:33,756 --> 00:30:36,616But somebody could replace a network card.

51700:30:37,086 --> 00:30:40,126You could be doing strangethings with virtualization.

51800:30:40,126 --> 00:30:41,546We'll talk about that later on.

519

00:30:41,736 --> 00:30:46,356But I mean, there's times where the MAC addresscan change, so this guarantees you that device


41/45

52000:30:46,356 --> 00:30:49,986within five minutes will be able tocommunicate or be learned or, you know,

521

00:30:49,986 --> 00:30:52,776that MAC address will be replacedon that switch if it stops talking.

52200:30:53,956 --> 00:30:56,546Welcome to the world of switching indeed.

52300:30:56,906 --> 00:30:59,206That is how a switch functions.

52400:30:59,206 --> 00:31:02,016That is its goal, is to bringtogether all the devices

52500:31:02,016 --> 00:31:05,896into a local area network andallow them to communicate.

52600:31:06,386 --> 00:31:08,776So what do we see, and what

do I want you to do with it?

52700:31:08,776 --> 00:31:10,076You see the bullets on the screen.

52800:31:10,076 --> 00:31:11,936Those are the major points that we hit.

52900:31:11,936 --> 00:31:18,206First thing I would like you to do is grab apiece of paper and in your own words write down,

53000:31:18,576 --> 00:31:25,606"A hub is this" or if maybe you're not awriter, you know, go to a friend, go to a spouse

53100:31:25,606 --> 00:31:27,906and explain to them, "A hub is this.

532

00:31:27,906 --> 00:31:30,846This is the difference betweena hub and a switch."


42/45

53300:31:31,036 --> 00:31:39,776Or, I do this sometimes: I'll be in Best Buyor one of the places where you just go and...

534

00:31:40,156 --> 00:31:44,216waste money on nonsense, but you'llbe in Best Buy and talk to one

53500:31:44,216 --> 00:31:48,016of the employees and seetheir perspective on it.

53600:31:48,016 --> 00:31:52,366I've got some very interesting results from

my surveys where you just go in and say, "Hey,

53700:31:52,366 --> 00:31:54,836I'm looking for a switch, just a small one.

53800:31:54,836 --> 00:31:55,646Where are those at?"

53900:31:55,646 --> 00:31:56,746"Oh, they're over here.

54000:31:56,746 --> 00:31:57,576Here's the box."

54100:31:57,576 --> 00:32:02,096And then throw this kind of question outthere, just say, "Actually somebody told me

54200:32:02,096 --> 00:32:04,246to get a hub, and someonetold me to get a switch,

54300:32:04,246 --> 00:32:06,156and then someone else saidthey're the same thing.

54400:32:06,836 --> 00:32:07,666What do you say?

545

00:32:07,666 --> 00:32:08,986What's best?"


43/45

54600:32:09,586 --> 00:32:10,346And see what they say.

54700:32:10,766 --> 00:32:14,806That is one of the most fun -- now,

don't throw them under the bus.

54800:32:14,806 --> 00:32:17,476Don't be like okay, "No,this is really how it works."

54900:32:17,476 --> 00:32:21,416But sometimes you'll get people who are likeninjas, that are like -- they know exactly.

55000:32:21,706 --> 00:32:23,056Other people will just say I don't know.

55100:32:23,056 --> 00:32:27,696Other people will just make up the most creativeand unique answers that you've ever seen.

55200:32:27,696 --> 00:32:29,766Sometimes they'll look at thebox and see if it says something.

55300:32:29,766 --> 00:32:30,716But it's fun.

55400:32:30,716 --> 00:32:31,906It's a fun survey to take.

55500:32:32,336 --> 00:32:35,586The second thing I want youto do is look at some devices

55600:32:35,586 --> 00:32:37,976and identify how many collision domains,

55700:32:37,976 --> 00:32:40,316how many broadcast domainsexist on each one of those.

55800:32:40,316 --> 00:32:44,306

Now, if these are all daisy-chainedtogether, if I take some cables and go clink,


44/45

55900:32:44,306 --> 00:32:48,326clink and link all these together,how many broadcast domains?

56000:32:49,146 --> 00:32:52,416

One. A broadcast will goeverywhere on those switches.

56100:32:52,416 --> 00:32:53,856How many collision domains?

56200:32:53,856 --> 00:32:54,926Well, start counting.

563

00:32:55,116 --> 00:32:57,526One, two, and that's the consoleboard, so don't count that one,

56400:32:57,526 --> 00:32:58,696you know, start counting those up.

56500:32:58,696 --> 00:33:03,846So if you're preparing for certification,be ready to answer those kinds of questions.

56600:33:03,846 --> 00:33:07,576You know, just based on these devices andhow they're connected, how many, you know,

56700:33:07,576 --> 00:33:09,276you'll see some hubs mixed in with switches.

56800:33:09,276 --> 00:33:11,256How many collision domains exist and all that.

56900:33:11,256 --> 00:33:12,056Now, there's a question.

57000:33:12,316 --> 00:33:16,136What if I take a hub and plugit into that switch port?

57100:33:16,456 --> 00:33:20,316Okay, now how many collision domains do I have?

57200:33:20,706 --> 00:33:24,096


45/45

You know, if I'm just talking aboutthat, that realm of it right now?

57300:33:24,836 --> 00:33:29,666One. It's just one because it doesn't matterhow -- even though I'm plugging into a switch,

57400:33:29,666 --> 00:33:34,006still only one device on thatport is able to send or receive.

57500:33:34,006 --> 00:33:36,896We've gone back down to half duplex --because we're in a hub -- at a time.

576

00:33:36,896 --> 00:33:38,516So again, drill yourself.

57700:33:38,516 --> 00:33:40,636Go through systems like that.

57800:33:40,636 --> 00:33:45,236And then finally, just understandhow the switch is doing what it does.

579

00:33:45,236 --> 00:33:48,876Look at that day in the life of a switchand see how it learns some MAC addresses

58000:33:48,876 --> 00:33:51,156and becomes just more efficient as it runs.

58100:33:51,646 --> 00:33:54,386I hope this has been informative for youand I'd like to thank you for viewing.

sub secription jerimy ccna 200-101 switching - welcome to the world of switching.txt

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