04 - cisco foundations - basic ip addressing1.txt

8/13/2019 04 - Cisco Foundations - Basic IP Addressing1.txt

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I was having a conversation with myaunt a couple weeks ago, who telecommutes,

works from home, works for a very large aircraftcompany, and she was having some computer issues

and I was, I can't just fix something,I always have to explain how it works.

And I said, "Okay, so you'vegot your computer here.

You want to go that website right?

So you're going to have to access it somehow."

And she turns and looks at me and she goes,"Oh, you mean like get to its IP address?"

[Laughing] And I said, "What doyou know about IP addresses?"

You know? And we kind of laughed and blew itoff, but my aunt is the least technical person

that I would, the least technical person I wouldever expect to wing out a term like IP address

to me, but that's how common it's become.

IP addressing rules the world.

It rules out everything communicateson the internet

and rules the realm of our Cisco networks.

So of course it's going to be

a massive topic of this series.

So let's get started in it.

This is going to be basic IP addressingwhere we understand what the IP address is.


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Kind of your digital home.

You get to know your neighborhood.

What IP addresses are around you.

Who can you talk to without intervention.

How to find your friends on thenetwork using a protocol called ARP.

And then I would say just a massive conceptthat I want to plant in your mind of,

how do you move around the network?

How do you combine layer 2 and layer

3 addresses together to communicate?

I'd like to think of IP addressingas your digital home.

Because it works that way in the real world.

You have a house.

You have an address for your house of 55

West East Street that you tell people, "Hey,

if you want to visit my housecome to 55 West East Street."

And they go, "Okay, great, I'llsee you there at 5 o'clock."

And that's how they reach you.

Well every single device that is connected

to a network also has anaddress known as an IP address.

That's how it communicates and that'show people know how to reach it.


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3600:01:53,546 --> 00:01:56,006So an IP address is four octets.

3700:01:56,006 --> 00:01:58,086So we'll just generate one here.

3800:01:58,086 --> 00:02:01,29610.5.9.52.

3900:02:01,606 --> 00:02:07,676Each one of these octets, each one of theseis an octet, has a value from 0 to 255.

4000:02:08,216 --> 00:02:10,316Now there are some specific rules.

4100:02:10,316 --> 00:02:13,486

Like I just can't come in there and say,"I want all zeros as my IP address."

4200:02:13,486 --> 00:02:16,276There are all 255's and there'seven rules beyond that.

4300:02:16,276 --> 00:02:18,836But we'll unfold those as we go.

44

00:02:18,836 --> 00:02:22,076For now, let's just know thatthose are all possibilities.

4500:02:22,076 --> 00:02:27,936I could have an IP address10.5.255.9 and that works a-okay.

4600:02:27,936 --> 00:02:31,326I mean these are all just potentialsthat I could assign to my computer.

4700:02:31,816 --> 00:02:36,206The rule is that every computer in thenetwork is going to need its own IP address.

4800:02:36,206 --> 00:02:40,516I mean you don't share an address with yourneighbor and you don't to these devices.


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4900:02:40,516 --> 00:02:42,006It has to be unique.

5000:02:42,416 --> 00:02:49,806Now these IP addresses are combinedwith a subnet mask, always, and usually,

5100:02:49,806 --> 00:02:51,876I'd say almost always, a default gateway.

5200:02:52,526 --> 00:02:58,126In a nutshell, the IP addressdefines your house or your location.

5300:02:58,126 --> 00:03:03,146So, this is how people reach meon the network and also the source

5400:03:03,146 --> 00:03:04,916that I come from when I try to talk to them.

5500:03:04,916 --> 00:03:08,686It's, you know, how they know to get back tome when I'm trying to communicate to them.

5600:03:09,216 --> 00:03:11,936The subnet mask defines your neighborhood.

5700:03:12,796 --> 00:03:17,216Okay, wait a sec, let's figure out whatthat means before we go any further.

5800:03:18,126 --> 00:03:19,826I've got the IP address right here.

5900:03:19,946 --> 00:03:24,626172.30.100.30.

6000:03:25,696 --> 00:03:36,066I combine that with the subnet mask255.255.255.0 is what I'm assigned to.

6100:03:36,066 --> 00:03:37,856Now, you as an administrator, set this up.

62


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00:03:37,856 --> 00:03:39,556You as an administrator assign those.

6300:03:39,786 --> 00:03:44,466Now at a base level, and trust me it will getmore advanced that this, but I'd say this is,

6400:03:44,646 --> 00:03:48,076for the vast majority of the networks ofthe world, this is all you need to know.

6500:03:48,526 --> 00:03:53,326Wherever you see 255, line that upto the IP address and say, "Okay.

6600:03:53,616 --> 00:03:58,876Those pieces of the addressrepresent my neighborhood or,

67

00:03:59,066 --> 00:04:00,796in technical words, my network."

6800:04:02,066 --> 00:04:04,146My common ground that I communicate on.

6900:04:04,796 --> 00:04:10,236Wherever I see a zero over here, thatrepresents who I am in that neighborhood or,

70

00:04:10,356 --> 00:04:12,966technically speaking, thehost of that neighborhood.

7100:04:13,626 --> 00:04:17,636Okay. So we've got these two key pieces.

7200:04:17,636 --> 00:04:21,916And before I even add in the defaultgateway, I want to make sure we unpack

7300:04:21,916 --> 00:04:23,966that and understand what that means.

7400:04:24,246 --> 00:04:31,696So if I am this computer, 172.30.100.30,and I'm plugged into a switch

75


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00:04:33,186 --> 00:04:41,516and I have another computer over there thatI want to talk to who's 172.30.100.150.

7600:04:41,896 --> 00:04:42,886Let's give them that IP address.

7700:04:42,886 --> 00:04:46,486Now assuming I just don't want to write it,they both have that subnet mask on there.

7800:04:47,016 --> 00:04:50,266I go under this computer, righthere, and I generate a ping.

7900:04:52,036 --> 00:04:54,026Now, what is a ping?

8000:04:54,026 --> 00:04:55,236

That's the first time we've seen it.

8100:04:55,376 --> 00:04:58,056It actually stands for Packet Internet Groper.

8200:04:58,056 --> 00:04:59,776That was the original name of it.

8300:04:59,776 --> 00:05:05,266It actually has been changed to be a little more

politically correct, but the goal of a Ping is

8400:05:05,266 --> 00:05:08,436to test connect network connectivityand if you're using a Windows PC,

8500:05:08,436 --> 00:05:11,636what it's actually doing isputting the entire alphabet.

86

00:05:11,696 --> 00:05:17,006I mean A through Z into a packet alongwith numbers 1, 2, 3, 4, 5, 6, 7, 8, 9.

8700:05:17,006 --> 00:05:21,116It throws it all into a packet andsends it to wherever you specify.

88


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00:05:21,326 --> 00:05:24,606And then when the other sidereceives it, it sends it back.

8900:05:24,606 --> 00:05:27,626It's a way of testing that we cancommunicate across the network, at least,

9000:05:27,876 --> 00:05:29,666by sending the alphabet to a device.

9100:05:29,666 --> 00:05:34,746And I will say Ping is your numberone network utility all the time.

9200:05:34,746 --> 00:05:37,726That will be your friend in the network world.

9300:05:38,946 --> 00:05:42,886

So, with this host, let'sgive a practical example.

9400:05:42,886 --> 00:05:45,346I'm going to open up my command prompts,

9500:05:45,346 --> 00:05:53,396that's where you would use Ping from,and type in Ping 172.30.100.150.

96

00:05:53,666 --> 00:05:56,976Now, I'm typing it right here, but I'm prettysure it won't work because I don't think

9700:05:56,976 --> 00:05:59,046that address exists, I'm justshowing you what I would type.

9800:05:59,616 --> 00:06:00,606What happens then?

9900:06:01,486 --> 00:06:04,726This computer and its internalbrain goes, "Okay.

10000:06:04,726 --> 00:06:08,586I'm trying to Ping 172.30.100.150.

101


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00:06:09,106 --> 00:06:09,696Interesting.

10200:06:10,196 --> 00:06:18,566Because I'm looking at subnet mask and I realize172.30.100.150 is in the same network as me."

10300:06:18,896 --> 00:06:20,106How do I know?

10400:06:20,106 --> 00:06:23,086Well, because he's in the same neighborhood.

10500:06:23,086 --> 00:06:27,126He has the same first three octetswhich I line up to my subnet mask

10600:06:27,126 --> 00:06:28,526and realize he's in my neighborhood.

10700:06:28,836 --> 00:06:34,496Now that's a huge point because whatthat tells him is I'm able to reach

10800:06:34,496 --> 00:06:37,886that device using a broadcast message.

10900:06:38,636 --> 00:06:43,756[Pause] This is number one

concept of the day right here.

11000:06:44,236 --> 00:06:48,716A broadcast message, meaning I can say,[yelling] "Hellooooo neighborhood!"

11100:06:48,716 --> 00:06:52,216I mean imagine yourself walkingout of your house with a megaphone

112

00:06:52,216 --> 00:06:54,266and going, "Helloooo my neighborhood!

11300:06:54,266 --> 00:07:01,936[echoing sound] I would like tospeak to [echo sound] Susan Newport!"

11400:07:02,046 --> 00:07:02,506


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You know [laughing].

11500:07:02,596 --> 00:07:05,156You're just yelling out with this megaphone.

11600:07:05,386 --> 00:07:09,016Everybody comes out of their houseand goes, "What's that guy doing?"

11700:07:09,016 --> 00:07:12,836And they're all like, "Well, he's lookingfor someone saying the name Susan Newport.

11800:07:12,836 --> 00:07:14,036Well that was disturbing.

11900:07:14,036 --> 00:07:16,296I'm going to go back in my housebecause I'm not Susan Newport."

12000:07:16,456 --> 00:07:19,536But somewhere down the street you hearthis little, [female voice] "Oh hello.

12100:07:19,846 --> 00:07:20,486That's me."

12200:07:20,836 --> 00:07:26,666And Susan comes running down to some, you know,

made-for-TV music and you guys are united.

12300:07:26,666 --> 00:07:29,456Right? Where did I go with that?

12400:07:29,456 --> 00:07:32,126So that's what the broadcast is there to do.

12500:07:32,416 --> 00:07:36,856Sometimes these analogies just come to me

and they just turn odd halfway through.

12600:07:36,856 --> 00:07:43,666He's going to send a broadcast, actually a veryspecially crafted one known as ARP broadcast.

12700:07:43,666 --> 00:07:45,266Address Resolution Protocol.


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12800:07:45,266 --> 00:07:49,016He's sending a message just like that,you know, I' m looking for Susan example.

12900:07:49,016 --> 00:07:53,256He's sending a message to his networkneighborhood saying, "Hello neighborhood!

13000:07:53,256 --> 00:07:56,316I'm looking for 72.30.100.150.

13100:07:56,316 --> 00:07:58,386Could that person please stand forward?"

13200:07:58,646 --> 00:08:02,626Now all of the devices receive that message.

133

00:08:02,626 --> 00:08:04,276They're all disturbed.

13400:08:04,846 --> 00:08:09,746But mind you, they have processorsthat can handle being disturbed.

13500:08:09,746 --> 00:08:13,256Broadcasts happen all the timein a local area network and most

13600:08:13,256 --> 00:08:15,196of them, these devices will ignore.

13700:08:15,196 --> 00:08:16,426This is a perfect example.

13800:08:16,426 --> 00:08:17,286He's saying, "Hello.

139

00:08:17,286 --> 00:08:18,686I'm trying to find 150."

14000:08:18,946 --> 00:08:21,466They receive it and they go, "Well, I'm not 150.

14100:08:21,466 --> 00:08:22,896I'm going back in my house."


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14200:08:23,006 --> 00:08:25,196This person receives it and goes, "Oh, oh.

14300:08:25,196 --> 00:08:26,586That's me, that's me, that's me!

14400:08:26,876 --> 00:08:29,406Let me send you, what's he trying to find?

14500:08:30,056 --> 00:08:32,406Let me send you my MAC address."

14600:08:33,006 --> 00:08:37,486Huge. ARP I call the MAC address sonar.

14700:08:37,806 --> 00:08:44,436Its goal is to, if I know what IP address I'm

trying to access, which in this case is 150,

14800:08:44,436 --> 00:08:48,756its goal is to figure out whatMAC address that device has.

14900:08:48,926 --> 00:08:52,456And in this case it's easybecause we're both on same network.

150

00:08:52,616 --> 00:08:57,386This guy can go, "Hello 172.30.100.150.

15100:08:57,386 --> 00:08:57,616Who are you?"

15200:08:57,616 --> 00:09:00,806He responds back with a unicast.

15300:09:01,556 --> 00:09:03,006

What is that?

15400:09:03,006 --> 00:09:08,066A direct message meaning he's going,"Okay, well I saw that broadcast come in

15500:09:08,226 --> 00:09:10,856and I saw the source MAC


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address that you're coming from.

15600:09:10,856 --> 00:09:13,516So I'm going to send a messagestraight back to you."

15700:09:13,516 --> 00:09:17,366Meaning I don't want to bother Boband Joe over here who's already had

15800:09:17,366 --> 00:09:19,386to be bothered by your initial broadcast.

15900:09:19,386 --> 00:09:25,146I'm just going to send my MAC addressdirectly back to you and now magic happens.

16000:09:25,446 --> 00:09:31,266Now this guys goes, "I have all the pieces of

the puzzle that I need to send my alphabet A,B,

16100:09:31,266 --> 00:09:33,796,D," you know, this is a PING message, right?

16200:09:33,796 --> 00:09:39,446This is the payload of what I'm trying tosend to the destination IP address of 150

16300:09:39,446 --> 00:09:46,246

from a source IP address of 30, to a destinationMAC address, again we have these two levels

16400:09:46,246 --> 00:09:48,576of addressing, we talked aboutthis in the previous nugget,

16500:09:48,916 --> 00:09:53,236to the destination MAC address of,well whatever this guy tells me.

16600:09:53,236 --> 00:09:55,976These MAC addresses are alsoa well known format.

16700:09:56,146 --> 00:09:56,676Let me show you.

168


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00:09:57,566 --> 00:10:00,186Open, oop, if I can get it open.

16900:10:00,446 --> 00:10:03,696Open a command prompt here andI'll do a, well let's do ARP-A,

17000:10:03,696 --> 00:10:06,216which actually shows al l the MAC addresses.

17100:10:06,216 --> 00:10:09,846It says, I want to know all the MACaddresses that you know about on your network.

17200:10:09,846 --> 00:10:13,756And, you know, I've got my ownlittle network here and this is me.

17300:10:13,756 --> 00:10:17,636

I'm 172.30.100.150.

17400:10:17,636 --> 00:10:19,476He's like oh well of courseI know my own MAC address.

17500:10:19,476 --> 00:10:24,036I learned about that because that's me, but I'vealso learned about the MAC address of my router.

176

00:10:24,586 --> 00:10:27,916These are all, let me giveyou the format of the MAC.

17700:10:28,216 --> 00:10:33,236MAC addresses are all 12characters long, hexadecimal.

17800:10:33,816 --> 00:10:37,736That means you have the option of0 through 9 at your disposable,

17900:10:37,916 --> 00:10:42,486as well as A through F. Theway that they look can differ.

18000:10:42,746 --> 00:10:50,276Windows formats them with, you know, 00-11-11,you know, it uses that kind of format.


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18100:10:50,536 --> 00:10:57,276I've seen plenty of other devices thatformat them like, you know, zero, zero:55:11.

18200:10:57,556 --> 00:11:04,666Other devices, yet, go in there, as a matter offact Cisco does this a lot, and says 0014-5192-,

18300:11:04,666 --> 00:11:07,186I mean you might go, "Well, come on!

18400:11:07,186 --> 00:11:08,536What's the standard?"

18500:11:08,746 --> 00:11:10,266They're all valid standards.

186

00:11:10,266 --> 00:11:14,546It just depends how the person decided toformat on it, but here's the common ground.

18700:11:14,866 --> 00:11:16,486They all have 12 characters.

18800:11:17,006 --> 00:11:23,736They all have values that will be 0 through 9or A through F for each one of those characters.

18900:11:24,046 --> 00:11:31,346So, my computer sends the broadcast messageout, gets the MAC address of this device back.

19000:11:32,636 --> 00:11:37,506Once that happens, he has everythingthat he needs to send his little A, B, C,

19100:11:37,506 --> 00:11:39,016D or whatever you're trying to send.

19200:11:39,016 --> 00:11:42,706You're sending an MP3 file, an e-mail, orwhatever you're trying to send over to that guy.

19300:11:42,706 --> 00:11:44,236He's got everything that he needs.


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19400:11:44,236 --> 00:11:45,576The destination MAC address.

19500:11:45,876 --> 00:11:49,056The source MAC address, ofcourse, because he knows who he is.

19600:11:49,306 --> 00:11:52,606Now that is sent in here andour switch does the magic.

19700:11:52,886 --> 00:11:54,496Remember, that's what switches do.

19800:11:54,496 --> 00:11:55,826Talked about that in the last nugget.

19900:11:56,076 --> 00:11:58,276

These are layer 2 devices.

20000:11:58,276 --> 00:11:59,896They learn MAC addresses.

20100:12:00,066 --> 00:12:04,816So as soon as he sings this, or as soon as hesees this PING message comes in and says, "Oh,

20200:12:05,086 --> 00:12:08,106

I see," as a matter of fact, hedoesn't even see the IP addresses.

20300:12:08,106 --> 00:12:10,026His functionality is limited.

20400:12:10,026 --> 00:12:11,876He doesn't even see what the message is.

20500:12:12,036 --> 00:12:16,066

All this switch does is say, "Okay I see thedestination MAC address you're trying to go to

20600:12:16,236 --> 00:12:20,806and I looked and I learned that that guygoes out port, you know, 9, on these.

20700:12:20,806 --> 00:12:22,246


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So I'm going to send that right out here.

20800:12:22,496 --> 00:12:25,816He receives the alphabet, he repliesback, kind of flips these around,

20900:12:25,816 --> 00:12:27,546says here's the source, here's the destination.

21000:12:27,546 --> 00:12:35,256So that is, oh, if I could emphasizehow amazingly important that concept is,

21100:12:35,256 --> 00:12:38,296and I know some of you aregoing, "Okay I get all that.

21200:12:38,296 --> 00:12:40,366I get that, but what's the dog?"

21300:12:40,916 --> 00:12:43,226[Laughing] I just realizedI have a dog on my site.

21400:12:43,406 --> 00:12:44,146This is ARP.

21500:12:44,566 --> 00:12:45,676That's what ARP is.

21600:12:45,676 --> 00:12:47,156ARP is a broadcast protocol.

21700:12:47,156 --> 00:12:48,996It's like that loud dog in your neighborhood.

21800:12:48,996 --> 00:12:52,996That's the analogy I was planning to usebefore, you know "Sound of Music" and Susan

21900:12:52,996 --> 00:12:54,916and everything else came out in my brain.

22000:12:55,166 --> 00:12:57,566There's a dog barking saying, "Hello, hello!

221


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00:12:57,566 --> 00:12:58,086Who is, who is?"

22200:12:58,086 --> 00:13:01,066You know and tried to resolvethe MAC address that way.

22300:13:01,416 --> 00:13:02,436But that's how it works.

22400:13:02,436 --> 00:13:04,766So, before I move on.

22500:13:05,816 --> 00:13:07,536Two more key facts.

22600:13:07,936 --> 00:13:12,336One, so that's what the [pause] subnet mask is.

22700:13:12,586 --> 00:13:15,006That's also, well hang on I said that backwards.

22800:13:15,006 --> 00:13:15,936That's what the IP address.

22900:13:15,936 --> 00:13:18,496That's also what this subnet mask is.

230

00:13:18,756 --> 00:13:24,676But we did everything that we did rightthere without the use of default gateway.

23100:13:25,226 --> 00:13:27,306And that's why I said usually a default gateway.

23200:13:27,656 --> 00:13:31,536In rare, rare, rare, rare,circumstances you might have that kind

23300:13:31,536 --> 00:13:32,886of network and that's all you want.

23400:13:32,986 --> 00:13:36,696You've got a bunch of devices plugged into aswitch and you just want them to communicate,

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00:13:36,876 --> 00:13:38,176you don't need a default gateway.

23600:13:38,696 --> 00:13:41,516Because I know you already havea feeling of where this is going.

23700:13:42,006 --> 00:13:43,786So what's the default gateway used for?

23800:13:46,136 --> 00:13:47,216[Pause] Get's you off your network.

23900:13:47,816 --> 00:13:52,346Gets you to some other network, which intoday's world most of the time is the internet.

24000:13:52,346 --> 00:13:54,446It doesn't always have to be,

but most of the time it is.

24100:13:54,446 --> 00:14:03,246So, this guy, let me fill this key piecein, he is that 172.30.100.30 and I'll use

24200:14:03,246 --> 00:14:05,206that same story from the last nugget.

24300:14:05,206 --> 00:14:07,516

He wants to go to the Bank of Arizona, right?

24400:14:07,646 --> 00:14:12,946So I go to a web browser andtype in Bankofarizona.com.

24500:14:13,416 --> 00:14:16,496The web browser, actually thePC goes out and finds out, "Oh,

246

00:14:16,496 --> 00:14:22,896the Bank of Arizona is theIP address 216.60.18.8."

24700:14:23,656 --> 00:14:24,466Let's write that up here.

24800:14:24,746 --> 00:14:31,326


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216.60.18.8.

24900:14:32,206 --> 00:14:34,846Come on , somebody is feelingthis puzzle piece fit right now.

25000:14:34,846 --> 00:14:35,646I can feel it.

25100:14:35,886 --> 00:14:37,886You're listening to me andyou're like, "Ugh, ugh, wait,

25200:14:38,026 --> 00:14:39,866are you going to say what Ithink you're going to say?

25300:14:39,866 --> 00:14:40,436I think so."

25400:14:40,866 --> 00:14:44,386So, going in here, he looksat his subnet mask, right?

25500:14:44,956 --> 00:14:47,396He goes, "Okay, I'm in the 172 neighborhood."

25600:14:47,876 --> 00:14:49,916He looks at this guy and goes, "Whoa!

25700:14:49,916 --> 00:14:50,946Stop the train right there.

25800:14:51,286 --> 00:14:52,586Not in my neighborhood."

25900:14:52,866 --> 00:14:56,476Now you can go through the rest of this and sayI'm in 30, he's in 60, I'm on 100, he's in 18.

26000:14:56,476 --> 00:15:00,386I mean these are as far apart as they couldpossibly be in the neighborhood world,

26100:15:00,506 --> 00:15:03,026but all it takes is just one ofthese numbers to be different


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26200:15:03,026 --> 00:15:07,846and he realizes this is not myneighborhood so, fit that piece together.

26300:15:08,406 --> 00:15:13,896He realizes I can't send an Arpmessage and reach that IP address.

26400:15:14,386 --> 00:15:18,786Why not? Because that ismission number two of a router.

26500:15:19,176 --> 00:15:22,046Remember router's mission numberone is to get you where you need

26600:15:22,046 --> 00:15:23,956to go based on IP address information.

26700:15:24,236 --> 00:15:28,556But mission number two is I stop broadcasts.

26800:15:28,556 --> 00:15:31,206That's really, when I, in thevery opening nugget, I said,

26900:15:31,206 --> 00:15:33,186"What's the fundamental function of the router?"

27000:15:33,316 --> 00:15:35,166It is to separate networks.

27100:15:35,266 --> 00:15:36,846This is how it does it.

27200:15:36,846 --> 00:15:42,406It keeps all of this broadcast traffic over hereand all of this broadcast traffic over here.

27300:15:42,776 --> 00:15:45,666Now, keep in mind there'sthousands and millions of routers

27400:15:45,666 --> 00:15:48,906out on the internet all keeping theirown broadcast traffic where it belongs,


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27500:15:49,196 --> 00:15:50,876but it separates the broadcast traffic.

27600:15:50,876 --> 00:15:55,126So he knows if he sends an ARP message,a broadcast, it will flood this network,

27700:15:55,386 --> 00:15:59,276but it will never, ever, ever reach Bankof Arizona which is out here somewhere

27800:15:59,276 --> 00:16:01,716in the cloud that he wants to get to.

27900:16:01,716 --> 00:16:03,636Because as soon as it reacheshere, it bounces off.

28000:16:03,636 --> 00:16:04,176Doing [phonetic].

28100:16:04,176 --> 00:16:05,326You know? It gets dropped.

28200:16:05,616 --> 00:16:10,046So, what he has to do, he goes, "Okay,I realize this is not on my network.

28300:16:10,346 --> 00:16:12,256I need to send this to my default gateway."

28400:16:12,516 --> 00:16:16,536Okay. If you're at a pointwhere you're like, "Okay.

28500:16:16,856 --> 00:16:18,376Hang on I need a process pause now."

28600:16:18,646 --> 00:16:23,556What I'm about to say is probably the mostimportant thing you will hear the rest

28700:16:24,286 --> 00:16:26,486of this day.

288


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00:16:26,486 --> 00:16:29,516[Laughing] You can probably tell I'mgiven to drama, but I'm kind of serious.

28900:16:29,696 --> 00:16:36,396So what this guy does, is he says, "I'mgoing to ARP, but not for this IP address.

29000:16:36,396 --> 00:16:38,506Because he knows that will be dropped.

29100:16:38,506 --> 00:16:43,906Instead, I'm going to send an ARPmessage for my default gateway.

29200:16:44,456 --> 00:16:47,336I want the MAC address for my default gateway

29300:16:47,486 --> 00:16:49,696

and this is the kind of packetI'm going to form.

29400:16:50,086 --> 00:16:52,836I'm going to send a Ping becausethat's just what I did or, you know,

29500:16:52,836 --> 00:16:55,056a $50.00 transfer or whateveryou're going to do.

29600:16:55,056 --> 00:16:55,976Ping is the alphabet.

29700:16:55,976 --> 00:17:02,206Right? A, B, C, D. I'm going to send a Pingto the destination IP address of the bank.

29800:17:02,816 --> 00:17:07,136The source IP address it'sgoing to come from is me.

29900:17:07,866 --> 00:17:13,446The destination MAC address it's going togo to is, come on, come on, fill it in.

30000:17:14,476 --> 00:17:15,156The gateway.


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30100:17:15,826 --> 00:17:16,606The router.

30200:17:16,946 --> 00:17:18,236This guy right here.

30300:17:18,486 --> 00:17:23,286The source MAC address it's going togo to or I should say come from, is me.

30400:17:24,386 --> 00:17:28,356This is what allows him to send a Pingmessage to the router because the switch,

30500:17:28,356 --> 00:17:30,196remember the switch doesn'teven see the IP address.

306

00:17:30,196 --> 00:17:31,526I kind of drew a line right here.

30700:17:31,526 --> 00:17:32,216No, it's right here.

30800:17:32,416 --> 00:17:34,206So the gateway is plugged into the switch.

30900:17:34,206 --> 00:17:36,546

He sends the message to the switch.

31000:17:36,756 --> 00:17:39,196The switch doesn't even seethe IP address he's going to.

31100:17:39,196 --> 00:17:40,586They don't have this capability.

31200:17:40,586 --> 00:17:42,296

They just look at MAC addresses.

31300:17:42,296 --> 00:17:44,216So, he sends it to the switch.

31400:17:44,386 --> 00:17:48,276The switch says, "Okay, I'm going to send itto the destination MAC address right here."


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31500:17:48,606 --> 00:17:49,546Which is the gateway.

31600:17:49,546 --> 00:17:51,216The gateway gets it and he's like, "Ooh!

31700:17:51,216 --> 00:17:52,016Ooh! Message for me!"

31800:17:52,206 --> 00:17:56,046But then when he looks further, because theseguys are layer 3 devices, network layer,

31900:17:56,286 --> 00:17:58,396he goes, "Ooh, this isn't for me.

32000:17:58,726 --> 00:18:02,906

This is for Bank of Arizona and I justhappen to know how to get you there.

32100:18:02,956 --> 00:18:06,086I'm going to send you outto the ISP as the next hop."

32200:18:06,576 --> 00:18:12,376That is, oh ok, rewind thosesix minutes and watch it again.

32300:18:12,376 --> 00:18:18,216Then rewind it again, show your friends, rewindit, like if I could just solidify that concept

32400:18:18,216 --> 00:18:22,086in your mind, you've gotnetworking fundamentals.

32500:18:22,186 --> 00:18:25,966Like that is such a big concept.

32600:18:26,116 --> 00:18:30,256Okay. I don't know, like this isrelated but not really at this point.

32700:18:30,256 --> 00:18:31,206I just kind of threw it in there.


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32800:18:31,206 --> 00:18:34,086This is like okay so you're studyingfor the exam, you got to know this,

32900:18:34,086 --> 00:18:35,656but we'll just throw it in there for now.

33000:18:35,976 --> 00:18:38,146There are three core class, okay, so right.

33100:18:38,656 --> 00:18:39,116Take this.

33200:18:39,116 --> 00:18:40,046Put it into a bucket, right?

33300:18:40,046 --> 00:18:43,896Set it aside and say, "That is my mastery of

information, this is something I just need

33400:18:43,896 --> 00:18:46,276to know if I have a question that asks me that."

33500:18:46,316 --> 00:18:51,346For now, three core classes of IP addresses,A, B, and C that we use in our networks today.

33600:18:51,346 --> 00:18:54,196

There are more, but those arethe three core that are in use.

33700:18:54,266 --> 00:18:58,576I know, the address is a certain, you know what?

33800:18:58,576 --> 00:19:02,356I'm not even going to go there.

33900:19:02,626 --> 00:19:07,446

When I put together that slide, youcould tell I was like, "Oh good.

34000:19:07,616 --> 00:19:08,476Oh good. Oh good."

34100:19:08,476 --> 00:19:11,126And then it popped in my head I'm like, "Oh


26/48

yeah, you'll need to know this for the exam."

34200:19:11,406 --> 00:19:13,726And we will, I know a lotof you are exam focused.

34300:19:13,726 --> 00:19:17,356And we will get back to the classes ofaddress, believe me, that is important.

34400:19:17,356 --> 00:19:19,286It's just right now this is so good.

34500:19:19,286 --> 00:19:24,416I don't want to, I don't want to have you putthat concept we just talked about in a bucket,

34600:19:24,416 --> 00:19:27,726and then, you know, almost get derailed and be

like, "Oh yeah, I have to study for the exam.

34700:19:27,726 --> 00:19:30,856It's like I want to just take it and runwith it, which is what I'm doing right here.

34800:19:30,946 --> 00:19:32,276I want to take that concept.

34900:19:32,276 --> 00:19:33,736

Let's open the bucket back up, right?

35000:19:34,286 --> 00:19:38,346And I want to put it togetherin network scenario as a whole.

35100:19:38,996 --> 00:19:43,686This, this, right here is how you explainto your friends and your spouse and your dog

352

00:19:43,686 --> 00:19:46,866and everybody else who will listento you, how you get to Google.

35300:19:47,656 --> 00:19:50,576You are sitting right here on the network.

35400:19:50,806 --> 00:19:53,926


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You have the IP address 172.30.100.50.

35500:19:53,926 --> 00:19:55,076Notice the subnet masks.

35600:19:55,076 --> 00:19:59,906So I immediately identify, that is my network,because I line up those first three octets

35700:19:59,906 --> 00:20:02,966and I have the default gatewayright here going to my router.

35800:20:02,966 --> 00:20:04,916Now I tried to color codethese just because, you know,

35900:20:04,916 --> 00:20:07,196when you're putting these things

together, you can't really fit it all.

36000:20:07,566 --> 00:20:10,626So the blue represents one network.

36100:20:10,626 --> 00:20:13,136So if, let's put the scenario in here.

36200:20:13,406 --> 00:20:21,186I Ping, [pause] let's give

the example 172.30.50.250.

36300:20:21,856 --> 00:20:22,816Which is this guy over here.

36400:20:23,306 --> 00:20:25,576Right? So I type that message into my computer.

36500:20:25,576 --> 00:20:26,356What happens?

36600:20:27,466 --> 00:20:29,406This computer looks at it and goes, "Okay.

36700:20:29,406 --> 00:20:31,526172. I like that, that's my network.

368


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00:20:31,636 --> 00:20:33,75630. Ooh, I like that too that's my network.

36900:20:34,066 --> 00:20:35,566Ooh, failure.

37000:20:35,706 --> 00:20:38,51650. No, no, no no, I'm on the 100 network."

37100:20:38,516 --> 00:20:41,006I immediately recognize it is a PC.

37200:20:41,106 --> 00:20:42,306That is not on my network.

37300:20:42,526 --> 00:20:47,656That, in my mind, says I cannot send anARP message for this address and expect it

37400:20:47,656 --> 00:20:52,316to get there because I know there's a brick wallof a router that's gonna receive that broadcast

37500:20:52,316 --> 00:20:55,456and drop it because, you know,it's going to say, "Well,

37600:20:55,456 --> 00:20:57,216you know, broadcasts are not allowed.

37700:20:57,216 --> 00:20:57,996I'm a router.

37800:20:57,996 --> 00:20:59,516I stop broadcasts."

37900:20:59,516 --> 00:21:03,976So this computer is smart enough to say,"Well, I need to get to this address,

38000:21:03,976 --> 00:21:06,776but I have to use my gateway to get there.

38100:21:07,276 --> 00:21:11,636So, he will send an ARP message, butit will be for this gateway right here.


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38200:21:12,096 --> 00:21:18,186It will say, "I am looking for 172.30.100.1.

38300:21:18,186 --> 00:21:19,576I know some of you are looking at this.

38400:21:19,576 --> 00:21:20,186Follow the lines.

38500:21:20,186 --> 00:21:21,216That's for the next network.

38600:21:21,216 --> 00:21:25,296So, "I am looking for 172.30.100.1.,"says the ARP message.

38700:21:25,296 --> 00:21:25,676Right here.

38800:21:25,676 --> 00:21:26,776He goes, "Oh, okay great!

38900:21:26,776 --> 00:21:27,336Here's my MAC address."

39000:21:27,336 --> 00:21:28,176My MAC address.

39100:21:28,176 --> 00:21:33,546My MAC address, let me fill inthe example, is 1111:1111:1111.

39200:21:33,676 --> 00:21:35,666Again, one of the formats of the MAC address.

39300:21:35,666 --> 00:21:36,776This guys goes, "Great.

39400:21:36,776 --> 00:21:37,716That's fantastic.

39500:21:37,716 --> 00:21:44,926I happen to be 111, oops, :1111:1111:1122.

39600:21:44,926 --> 00:21:45,986


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That's my MAC address.

39700:21:45,986 --> 00:21:47,656Just because Jeremy can write that really fast.

39800:21:47,866 --> 00:21:49,596So, I'm going to create a packet.

39900:21:49,596 --> 00:21:52,236I'm going to have that Pingbe the data that I'm sending.

40000:21:52,236 --> 00:21:53,016It's the alphabet.

40100:21:53,416 --> 00:21:57,626Destination IP address, now you fill inthis box, what is the destination IP?

40200:21:58,596 --> 00:22:01,306[Pause] 172.30.50.250.

40300:22:01,646 --> 00:22:02,476That's where I'm going.

40400:22:02,476 --> 00:22:04,046That's my end destination.

405

00:22:04,296 --> 00:22:05,276That will not change.

40600:22:05,726 --> 00:22:08,346I have the source IP address of who?

40700:22:09,136 --> 00:22:12,356Me. 50. That's where I came from.

40800:22:12,356 --> 00:22:14,876

172.30.100.50.

40900:22:14,876 --> 00:22:17,556And know that I'm just writing this in herebecause I can't squeeze that whole address

41000:22:17,556 --> 00:22:19,176in there, but it is the full


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IP address in there.

41100:22:19,276 --> 00:22:27,126So then I'm also going to add indestination MAC address of 1111:1111:1111.

41200:22:27,286 --> 00:22:27,756Who is that?

41300:22:28,856 --> 00:22:30,116Gateway. Default gateway.

41400:22:30,116 --> 00:22:32,406Router. That is able to getme out of my neighborhood.

41500:22:32,736 --> 00:22:34,046Source MAC address.

41600:22:34,806 --> 00:22:38,6261111:1111:1122.

41700:22:39,666 --> 00:22:43,026Right? SO that is now a craftedpacket that will work.

41800:22:43,196 --> 00:22:44,276Comes into the switch.

41900:22:44,276 --> 00:22:45,596Switch. What does it read?

42000:22:45,786 --> 00:22:47,146MAC address info, that's it.

42100:22:47,146 --> 00:22:50,386It goes, "okay, I know because I'mlooking at my MAC address table

42200:22:50,386 --> 00:22:53,396that the destination MACaddress of this is out port 9."

42300:22:53,396 --> 00:22:54,446Again, I'll go there.

424


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00:22:54,446 --> 00:22:57,316So, that now delivers thePing message to this router.

42500:22:57,656 --> 00:23:02,226Router gets it he's like, "Ooh, ooh, mail forme, because I see my destination MAC address."

42600:23:02,466 --> 00:23:05,426He then looks further andsays, "Oooh, that's not for me.

42700:23:05,976 --> 00:23:09,146That's going to 172.30.50.250."

42800:23:09,146 --> 00:23:10,826Looks at his routing table.

42900:23:12,036 --> 00:23:12,756

Comes over here.

43000:23:13,496 --> 00:23:21,856Routing table has all the places he knows how toreach and one of them happens to be 172.30.50.0.

43100:23:22,586 --> 00:23:26,006Oh man I just, it's likemy hand moved without me

432

00:23:26,006 --> 00:23:28,396and it introduced a wholelot of concepts right there.

43300:23:29,296 --> 00:23:33,296/24 is a shorthand notationfor that subnet mask.

43400:23:33,686 --> 00:23:35,566And that's all I'm goingto say about it right now.

43500:23:35,566 --> 00:23:38,166We'll get there, it really hasto do with binary behind it.

43600:23:38,626 --> 00:23:42,366The 0 address represents the network.


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43700:23:42,846 --> 00:23:52,436Meaning I am not allowed to use 172.30.50.0and assign that to any computer on that network

43800:23:52,436 --> 00:23:54,646because this represents the network as a whole.

43900:23:54,826 --> 00:23:59,326The only place I'm going to see that address,that .0 address, is in a routing table

44000:23:59,326 --> 00:24:03,466because that router says this is howI know how to reach that network.

44100:24:03,466 --> 00:24:05,366That identifies the whole network to me.

442

00:24:05,366 --> 00:24:06,286The 0 address.

44300:24:06,526 --> 00:24:11,716While we're on the topic, the last address canbe used to send a broadcast message to everybody

44400:24:11,716 --> 00:24:13,256on that network, but that's later.

445

00:24:13,256 --> 00:24:15,056That's like the classes of addresses, right?

44600:24:15,176 --> 00:24:17,446Key information you'll needto know, but not yet.

44700:24:17,446 --> 00:24:20,826So this router looks at its routing tableand says, "Oh, I know how to get there.

44800:24:20,996 --> 00:24:27,376Ooh, ooh. And my routing table tells me thatto get there, I need to send it to 10.5.1.2."

44900:24:29,006 --> 00:24:31,356[Pause] How did it know that?

450


34/48

00:24:31,856 --> 00:24:34,466Well that's where you gotinvolved as a Cisco admin.

45100:24:34,466 --> 00:24:35,966We have to get paid for something, right?

45200:24:36,156 --> 00:24:38,456You went onto that router and educated it.

45300:24:38,716 --> 00:24:42,116You could either educate itstatically and say, "Hey router,

45400:24:42,116 --> 00:24:44,546to get to that network go to that IP address."

45500:24:44,546 --> 00:24:49,176That's considered your next hop IP address or

you can let the routers do the work for you

45600:24:49,176 --> 00:24:51,536and use something known asa dynamic routing protocol.

45700:24:51,746 --> 00:24:53,126But, again, more on that later.

45800:24:53,126 --> 00:24:54,946

For now, we'll just say the router knows.

45900:24:54,946 --> 00:24:57,116The router knows how to getthere, so what does it do?

46000:24:57,116 --> 00:24:58,536Because we're talking foundations here.

46100:24:58,886 --> 00:25:01,816

It will tear off, I'm busting out a red marker,

46200:25:02,166 --> 00:25:05,886tear off the original sourceand destination MAC address.

46300:25:06,706 --> 00:25:08,046Because it doesn't need it anymore.


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46400:25:08,356 --> 00:25:13,016That was valid for this network to allowthese guys to talk, but now it will replace it

46500:25:13,136 --> 00:25:16,486with the source and destination, andfor now, we'll just say MAC address.

46600:25:16,486 --> 00:25:19,886It could be other things depending on the kindof network, but most of the time it will be.

46700:25:20,156 --> 00:25:25,196It will replace it with this MACaddress and that MAC address.

46800:25:25,376 --> 00:25:27,146A new source and a new destination.

46900:25:27,276 --> 00:25:29,776Which will be different from this one.

47000:25:29,776 --> 00:25:34,236Every network card in the worldhas its own unique MAC address.

47100:25:34,426 --> 00:25:37,406So, you'll never have a duplicate of

those unless you buy really cheap,

47200:25:37,406 --> 00:25:40,896knockoff network cards, atwhich point, buyer beware.

47300:25:41,316 --> 00:25:44,486So, he replaces and says, "Okay,I'm going to do the ARP here.

474

00:25:44,636 --> 00:25:45,586I've got a new source.

47500:25:45,586 --> 00:25:46,696A new destination."

47600:25:46,856 --> 00:25:49,786Put that on there and that


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gets the packet to right here.

47700:25:50,086 --> 00:25:55,546This guy looks at his routing table and he goes,again, this never changed, this never changed.

47800:25:55,546 --> 00:25:56,246He goes, "Ooh, ooh.

47900:25:56,396 --> 00:26:02,416I've got a message here from 172.30.50.250,"and I'm looking at my router and going matter

48000:26:02,416 --> 00:26:04,636of fact I am plugged right into that network.

48100:26:05,156 --> 00:26:07,286He'll actually see a route in his routing table.

48200:26:07,286 --> 00:26:13,096172.30.50.0 send it out yourEthernet interface right here.

48300:26:13,346 --> 00:26:16,396You know? It'll be right in there,he's like, "Oh, I'm plugged into it.

48400:26:16,396 --> 00:26:20,276Great." So what I will do is I

will send ARP message to find

48500:26:20,276 --> 00:26:22,766out what the MAC addressof this server really is.

48600:26:22,766 --> 00:26:24,426Because I know that's where I have to go.

48700:26:24,576 --> 00:26:30,696

So it resolves, via an ARP message, hisMAC address puts itself as the new source

48800:26:30,866 --> 00:26:33,236and now we have the Pingmessage that goes right here.

48900:26:34,376 --> 00:26:35,266


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Isn't that amazing?

49000:26:35,606 --> 00:26:39,266It's the same thing very similar to whatI was talking about in the last nugget,

49100:26:39,536 --> 00:26:44,096I just like covering this multiple times becauseit's a huge concept and I want it to go deep.

49200:26:44,386 --> 00:26:48,176It's got to go deep in you becausethis is the core of how networks work.

49300:26:48,176 --> 00:26:50,296This is also the core ofeverything troubleshooting

49400:26:50,486 --> 00:26:55,366

if your network is not working is this,this little layer 2/layer3 address game

49500:26:55,366 --> 00:26:57,126to help us move all around the network.

49600:26:57,506 --> 00:27:00,976An analogy, if you're an analogykind of a visual person like I am.

497

00:27:01,426 --> 00:27:06,396I think of this layer 3/layer2 as like a GPS system.

49800:27:06,576 --> 00:27:10,636Where I'm sitting here in Arizona andI want to drive my car up to Canada.

49900:27:10,856 --> 00:27:14,286You know. We'll say 1,500 miles away.

50000:27:14,596 --> 00:27:18,896Now, I know that I need to get thereand that's what I put in my GPS system,

50100:27:19,176 --> 00:27:23,286but I have to have all these waypoints,because I'm a man, I'm not a machine.


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50200:27:23,286 --> 00:27:27,316I have to get gas, I have to get coffee,I have to get food along the way.

50300:27:27,556 --> 00:27:32,986But in all of these little waypoints, Inever, you know, replace the end destination

50400:27:32,986 --> 00:27:34,726in my GPS system with a waypoint.

50500:27:35,026 --> 00:27:38,156You know, if I'm like, "Okay I want tostop at the Circle K here on the corner,

50600:27:38,386 --> 00:27:43,856that's waypoint number three," but I'mnever going to lose, I'm going to Canada.

50700:27:44,036 --> 00:27:49,266You know I'm going to 55 North Elm Street inCanada because if I do then I'll just stop

50800:27:49,266 --> 00:27:53,016in at Circle K and get stuck there forever andthat's where I'll live my life and then die.

50900:27:53,116 --> 00:27:54,536Which is what would happen to a packet.

51000:27:54,806 --> 00:27:57,576So all of these are the layer 2 addresses.

51100:27:57,786 --> 00:28:00,876We have to have these to get hopby hop by hop by hop, you know,

51200:28:00,876 --> 00:28:05,786to reach the different devices and, for

every single network needs its own set

51300:28:06,076 --> 00:28:11,646of layer 2 addresses, but all along we keepthis the same because otherwise we lose

51400:28:11,646 --> 00:28:14,716where we originally came from


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and where we're finally going.

51500:28:15,766 --> 00:28:17,576Poof! All my scribbles disappear.

51600:28:17,576 --> 00:28:19,436And there's one more thing I wanted to add.

51700:28:19,926 --> 00:28:22,246I added this internet cloud here for a reason.

51800:28:22,906 --> 00:28:28,376When my device sends data and it ends upreaching this router, that's again the goal

51900:28:28,376 --> 00:28:32,706of the router is to figure out where tosend that data based on its IP address.

52000:28:32,706 --> 00:28:36,296If I'm sending it to the server, it's goingto go, "Okay, I know how to get there.

52100:28:36,296 --> 00:28:38,416I go out this cable right here."

52200:28:39,256 --> 00:28:43,386If I'm sending to somethingthat's not this IP address,

52300:28:43,626 --> 00:28:46,606it's likely going to havesomething called a default route.

52400:28:47,456 --> 00:28:49,856A default route looks like all zeros.

52500:28:49,856 --> 00:28:51,846It's kind of like a default

gateway for a router.

52600:28:51,846 --> 00:28:55,066But routers don't have defaultgateways because they're routers,

52700:28:55,066 --> 00:28:57,656and they are the default


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gateway that things go to.

52800:28:57,656 --> 00:29:00,756So, it has what's called a defaultroute that says, "You know what?

52900:29:00,756 --> 00:29:02,866If you don't know where tosend it little router,

53000:29:03,216 --> 00:29:05,996why don't you send this off to the internet?"

53100:29:06,256 --> 00:29:09,826Now, I know in the picture, and you'll seeit in diagrams all the time, it looks like,

53200:29:09,826 --> 00:29:11,976okay, it's the "Finding Nemo" right?

53300:29:11,976 --> 00:29:13,146Its like, "Go fish.

53400:29:13,146 --> 00:29:14,116Find your home on the internet."

53500:29:14,116 --> 00:29:16,486But really it's far more technical than that.

53600:29:16,686 --> 00:29:19,236There's really a router right here at your ISP.

53700:29:19,236 --> 00:29:23,226You know? Whoever your ISP is, it says,"Here's the MAC address of that router,

53800:29:23,226 --> 00:29:27,266I will send it there," and this littlelayer 2/layer 3 game goes all the way

53900:29:27,556 --> 00:29:31,246until it finds whatever server you'retrying to reach out here on the internet.

54000:29:31,526 --> 00:29:33,296So the router is the decision point.


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54100:29:33,446 --> 00:29:36,546Most of them have a defaultroute for the internet.

54200:29:36,546 --> 00:29:37,596Now, how come?

54300:29:37,596 --> 00:29:42,106Is there a way that this guy could actuallyknow every single network in the internet?

54400:29:42,646 --> 00:29:44,066Actually there is.

54500:29:44,466 --> 00:29:49,246It's something called, BGP,which is the protocol

546

00:29:49,246 --> 00:29:52,656that holds all of the routes of the internet.

54700:29:52,656 --> 00:29:58,696But, 90 percent, if not more, of the routersjust don't have the capacity for that.

54800:29:58,956 --> 00:30:01,376You're Linksys or Netgear at home.

549

00:30:01,376 --> 00:30:08,026No way. Most Cisco routers that you use[pause] in small office, home office,

55000:30:08,076 --> 00:30:13,646small mid-size networks, won't have the memorycapacity to hold the BGP and when you get

55100:30:13,646 --> 00:30:15,516into the realm it just becomes massive.

55200:30:15,516 --> 00:30:19,816So instead, what we do is say you know, "Okay,I know specifically how to get to that one.

55300:30:19,816 --> 00:30:22,966I know specifically how to get hereand there and to all my networks inside


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55400:30:22,966 --> 00:30:27,476of my organization, but when it comes to theinternet, I'm going to use that default route,"

55500:30:27,476 --> 00:30:30,026which says, "Here's how youreach everything else."

55600:30:30,836 --> 00:30:34,276So what did we see here and whatdo I want you to do with it?

55700:30:34,386 --> 00:30:37,826Well what we saw is the IPaddressing, the fundamentals of it,

55800:30:37,826 --> 00:30:43,606we saw how the devices are addressed, how theyfigure out what neighborhood they are based

55900:30:43,606 --> 00:30:46,076on their subnet mask and findingtheir friends using the ARP,

56000:30:46,076 --> 00:30:49,196and also finding their default gatewayif they want to be able to get off

56100:30:49,196 --> 00:30:51,366

of their network or get out their neighborhood.

56200:30:51,706 --> 00:30:55,416But I would say the most importantconcept of all was that culmination

56300:30:55,416 --> 00:31:00,126of how the layer 2/layer 3 addressingworks together, works with each other

564

00:31:00,126 --> 00:31:02,156to help deliver the messagewhere it needs to go.

56500:31:02,766 --> 00:31:05,696Now what I want you to dowith this is a few things.

566


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00:31:05,696 --> 00:31:09,126And again, some major conceptsthat we discussed here.

56700:31:09,486 --> 00:31:13,016I want you to go on your computer,whether it be at work or at home,

56800:31:13,016 --> 00:31:14,786and start proving it to yourself.

56900:31:14,816 --> 00:31:19,066First off, do an IP config and by theway, if you are studying for the exam,

57000:31:19,496 --> 00:31:23,746you will need to know basic command lineutilities like IP config, Ping, ARP,

571

00:31:23,746 --> 00:31:25,676you know the utilities thatI've been using so far,

57200:31:26,016 --> 00:31:30,026and you can see that I have a local areaconnection, this is my network card.

57300:31:30,406 --> 00:31:34,596And right here I have anIPv4 address 172.30.100.72.

57400:31:34,676 --> 00:31:37,556I want you to, you know, findout what your IP address is.

57500:31:37,556 --> 00:31:38,986Find out what your subnet mask is.

57600:31:38,986 --> 00:31:40,286What your default gateway is.

57700:31:40,286 --> 00:31:42,256I want you to Ping your default gateway.

57800:31:42,456 --> 00:31:47,626You know go in there and Ping it, [pause]to make sure that you're getting responses.


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57900:31:47,626 --> 00:31:49,736You should get replies backfrom your default gateway.

58000:31:49,996 --> 00:31:55,196Then do an ARP-A to find out what theMAC address of your default gateway is.

58100:31:55,496 --> 00:31:59,476If you're curious, thesethings last for five minutes.

58200:31:59,476 --> 00:32:03,416If you don't use them for five minutes, they'lldisappear out of, it's called your ARP cash.

58300:32:03,666 --> 00:32:06,256You can manually clear them doing an ARP-D.

58400:32:06,626 --> 00:32:07,836And I can say, "Okay.

58500:32:07,836 --> 00:32:08,456What's left?

58600:32:08,456 --> 00:32:09,486Nothing. It's all gone."

587

00:32:09,486 --> 00:32:14,756So now when I Ping it again,notice that I see it in there.

58800:32:15,296 --> 00:32:17,686Now, here's an interesting test.

58900:32:17,686 --> 00:32:20,746I'm like, "Do I want show this to youor do I want to leave this to you?"

59000:32:21,366 --> 00:32:22,946Try Pinging an internet address.

59100:32:22,946 --> 00:32:23,906Do an ARP-E.

59200:32:24,456 --> 00:32:26,486


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[Pause] I'll do it with you.

59300:32:26,606 --> 00:32:28,166Just in case you don't have a computer nearby.

59400:32:28,526 --> 00:32:29,226[Laughing] Wait a sec.

59500:32:29,346 --> 00:32:30,826What are you watching me on?

59600:32:30,826 --> 00:32:34,426So ARP-D. And I see thereis no ARP entries found.

59700:32:34,606 --> 00:32:37,906Now I'm going to a Ping to an internet address.

598

00:32:37,906 --> 00:32:41,0064222. It's actually a DNSserver out in California.

59900:32:41,426 --> 00:32:42,266I just Pinged that.

60000:32:42,576 --> 00:32:45,706If I do an ARP-A, what do I expect to see there?

601

00:32:46,196 --> 00:32:50,156The MAC address of 4222 or something else?

60200:32:51,516 --> 00:32:51,956[Pause] Hmm.

60300:32:52,456 --> 00:32:53,486Something else.

60400:32:53,836 --> 00:32:58,326

Notice that I never figure out whatthe MAC address of that device is.

60500:32:58,326 --> 00:32:59,996How come? It's not on my network.

60600:32:59,996 --> 00:33:03,186My computer is smart enough


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to know, "Oh you have to,

60700:33:03,186 --> 00:33:05,286you have to default gateway to get there."

60800:33:05,486 --> 00:33:07,326So I know his MAC address,that's how I get there,

60900:33:07,326 --> 00:33:10,346but my computer will never, ever, ever know.

61000:33:10,346 --> 00:33:14,246And nor will I have a way of ever findingout unless I give them a phone call.

61100:33:14,246 --> 00:33:17,466What the MAC address is of that destinationserver I'm reaching because it's not

61200:33:17,466 --> 00:33:19,226on my network, it's in another world.

61300:33:19,576 --> 00:33:23,576So, do these kinds of things and I would say,you know, if you're not too sure what to Ping,

61400:33:23,576 --> 00:33:24,976you know, start trying to find other addresses.

61500:33:24,976 --> 00:33:29,116Just like I know there is there's25, that's my storage server

61600:33:29,116 --> 00:33:30,646at my house, and I can start saying, "Okay.

61700:33:30,646 --> 00:33:33,086Now that's starting to show up in the list."

61800:33:33,346 --> 00:33:37,036You might go on the internetand grab a fun utility called,

61900:33:38,186 --> 00:33:43,846[pause] if I can type it inhere, "Angry IP Scanner."


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62000:33:45,306 --> 00:33:47,076Just a fun little guy.

62100:33:47,316 --> 00:33:48,596Download the old version.

62200:33:48,596 --> 00:33:51,186It's actually much simpler,I think, than the new one.

62300:33:51,486 --> 00:33:54,896Go with the old Windows version.

62400:33:54,896 --> 00:33:56,046Stable and widely used.

62500:33:56,046 --> 00:33:56,866

Go for that.

62600:33:57,106 --> 00:34:01,806And do a scan of all the IP addresses inyour house and create a network diagram.

62700:34:01,976 --> 00:34:03,146You know? Draw it up.

62800:34:03,226 --> 00:34:04,546

Just like I've been doing all throughout.

62900:34:04,546 --> 00:34:06,256You know, draw, okay you've got the computer.

63000:34:06,456 --> 00:34:07,616Over here, here's his IP.

63100:34:07,616 --> 00:34:09,376Here's his MAC address.

63200:34:09,446 --> 00:34:12,526I've got, you know, the switch,which probably is invisible.

63300:34:12,526 --> 00:34:13,896I've got a router over here.


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63400:34:13,896 --> 00:34:15,046I've got some other devices.

63500:34:15,046 --> 00:34:16,256My Nintendo Wii.

63600:34:16,636 --> 00:34:18,606I've got, you know, my X-Box.

63700:34:18,606 --> 00:34:21,656You know. Whatever else youfind on that or diagram it out.

63800:34:21,656 --> 00:34:24,626Just to start really, you get the concept here.

63900:34:24,626 --> 00:34:27,686I need you to take this and start using it.

64000:34:27,936 --> 00:34:30,466Applying it to things thatyou do every single day.

64100:34:30,466 --> 00:34:33,936I hope this has been informative for youand I'd like to thank you for viewing.

04 - cisco foundations - basic ip addressing1.txt

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