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00:00:00 - Well hello everyone. 00:00:01 - Anthony Sequeira here, and it is
my great privilege to walk 00:00:06 - you through CCNA data center here
at CBT Nuggets. 00:00:11 - We're going to get started with
this series on 640-911, 00:00:15 - that's the introduction to Cisco
Data 00:00:17 - Center Networking exam.
00:00:19 - We're going to have you completely prepared for that
00:00:22 - exam, but most importantly, we're going to make sure you
00:00:26 - understand fundamentally data center networking
00:00:29 - technologies. 00:00:30 - In this first Nugget, we're going
to get started with the 00:00:33 - important OSI model.
00:00:35 - Now typically when an instructor mentions the OSI
00:00:38 - model, students get up and leave, or if they're watching
00:00:43 - a computer presentation, they open their
00:00:45 - email or surf the web. 00:00:47 - Stay with me people.
00:00:49 - This is actually going to be enjoyable. 00:00:51 - And we're going to do something
that a lot of 00:00:53 - instructors forget to do and that's
clearly show you why a 00:00:58 - mastery of the OSI model is really
going to help you with 00:01:02 - data center networking.
00:01:04 - I'm not kidding. 00:01:05 - It's really going to help.
00:01:06 - We'll also, obviously, review exactly what this model is.
00:01:10 - And we've got a bonus in this Nugget, we're going to take a
00:01:12 - look at a model that actually predates the OSI model and
00:01:16 - we'll analyze the important TCP/IP model as well.
00:01:21 - You know, one hero that I've always had in
00:01:23 - my life is my dad. 00:01:25 - When I was a little kid I would
watch my dad do 00:01:27 - something amazing.
00:01:29 - I would watch him build a house from the ground up.
00:01:32 - And it was much later in life, like now, that I realized
00:01:36 - building a house isn't all that incredibly difficult
00:01:40 - because he did it in modules. 00:01:44 - He would first build a foundation.
00:01:47 - Then after building a foundation, he would go in and
00:01:50 - he would frame the house. 00:01:52 - Then after framing the house, he
would go in and he would 00:01:55 - install the electric and the plumbing
inside the house. 00:01:59 - And then he would go ahead and
he would do some finish work 00:02:02 - inside those walls that he had
constructed. 00:02:05 - And notice my house looks really
weird, but anyways, 00:02:09 - building that complex house in
a modular fashion actually 00:02:16 - makes it much simpler than you
might think. 00:02:19 - This is one of the reasons why
we need an OSI model. 00:02:24 - We need to take something really,
really complex, like 00:02:27 - networking, and we need to break
it down 00:02:30 - into simplified chunks.
00:02:33 - And that's one of the things the OSI model brings.
00:02:37 - Now another important reason the OSI model was invented was
00:02:40 - because we would have equipment manufacturers, like
00:02:43 - for instance, how about Digital Equipment Corporation,
00:02:47 - they would be creating networking stuff and they
00:02:51 - would be using their own techniques and standards.
00:02:54 - And then you would have IBM over here and they're creating
00:02:57 - cool network gadgets, but they're using their own set of
00:03:00 - standards and design techniques. 00:03:03 - And sure enough, the devices would
not be able to, what we 00:03:07 - call, inter-operate.
00:03:09 - So a nice model that could be used as a guide for networking
00:03:14 - equipment manufacturers was needed so that this stuff
00:03:17 - could play together nicely. 00:03:20 - Now another reason we might need
the OSI model is so that 00:03:22 - we can accurately teach someone
about data center 00:03:26 - networking.
00:03:28 - Yeah, if I'm going to teach you a complex subject, I
00:03:32 - really need to break it down into layers so that we don't
00:03:36 - get overwhelmed with the subject as a whole.
00:03:40 - But I know, I know, I know what you're thinking.
00:03:42 - You're thinking, Anthony, look, I'm not going to be
00:03:45 - making networking equipment in my backyard.
00:03:48 - I'm not going to be teaching this to anyone.
00:03:51 - Please give me some compelling reason about why I should go
00:03:57 - through the pain of this theoretical model mastery.
00:04:02 - Well let me tell you why-- 00:04:04 - two big important letters in our
world-- 00:04:09 - TS.
00:04:10 - What does this stand for? 00:04:12 - Troubleshooting.
00:04:13 - We want to master the OSI model because when we're in
00:04:19 - the data center infrastructure and we must troubleshoot
00:04:24 - problems, this OSI model mastery can really enhance our
00:04:30 - troubleshooting skills. 00:04:32 - And throughout this CBT Nugget
series, I will 00:04:35 - prove this to you.
00:04:37 - For right now, you just need to trust me, but you will see
00:04:40 - how the OSI model can benefit us when troubleshooting.
00:04:45 - Now what is the OSI model really? 00:04:49 - Well it's a simple seven layer
model that we use for all the 00:04:53 - great advantages that we've mentioned.
00:04:56 - Now the first thing that you're going to want to do for
00:04:58 - mastery of the model is you're going to want to memorize the
00:05:01 - seven layers in their order. 00:05:03 - There's two common ways that you
can do this. 00:05:05 - You can memorize it utilizing a
mnemonic device starting 00:05:10 - from the top and going down to
the bottom. 00:05:12 - The most popular one in this direction
is All People Seem 00:05:18 - To Need Data Processing.
00:05:21 - But I don't know about you, I love food.
00:05:24 - So I like to memorize it from the bottom up with the popular
00:05:27 - mnemonic device Please Do Not Throw Sausage Pizza Away.
00:05:33 - Yeah, I really identify with that one.
00:05:35 - So no matter how you do it, first step, let's memorize
00:05:40 - those seven layers. 00:05:42 - Now let me let you in on a little
secret. 00:05:44 - As a data center networking engineer,
you're going to make 00:05:49 - your money at the lower four layers.
00:05:53 - Those are the ones that are going to be important to you.
00:05:55 - In fact, data center networking engineers typically
00:05:58 - just say this is L1, L2, L3, and L4.
00:06:03 - So you won't really hear them say the data link layer.
00:06:06 - You'll hear them simply say layer two.
00:06:09 - You might not hear them say the transport layer.
00:06:11 - You'll hear them say layer four. 00:06:14 - So let's keep that in mind, that
often the lower four 00:06:17 - layers, so important to us, are
just going to be Layer 1, 00:06:20 - Layer 2, Layer 3, Layer 4.
00:06:22 - Hey, I've got a Layer 1 problem. 00:06:23 - You would know immediately that
that person is talking 00:06:26 - about a physical layer issue.
00:06:30 - How does the engineer refer to these layers?
00:06:32 - Well they'll typically just say, hey, that's an upper
00:06:35 - layer problem, and oftentimes, this may be a problem in the
00:06:39 - application itself that is utilized in the data center.
00:06:43 - And that oftentimes might be someone else's problem.
00:06:47 - Now let's zero in on what each of these layers is defining.
00:06:52 - The physical layer is indeed defining the physical stuff,
00:06:56 - like a great example of this would be the cabling.
00:07:00 - Sure, we know we're going to be using technologies in the
00:07:03 - data center like gigabyte ethernet and fiber channel.
00:07:08 - And these technologies are going to be run over physical
00:07:11 - cables, and this is stuff of the physical layer.
00:07:15 - I hear some instructors say well, the physical layer is
00:07:18 - the stuff you can see and touch. 00:07:21 - Be careful of this, right?
00:07:22 - Because what about the case of wireless?
00:07:25 - Sure, there's going to be a physical layer for wireless,
00:07:29 - but it's not something that we can see with the human eye.
00:07:32 - Now what device would you have at the physical layer?
00:07:37 - We'll talk more in detail about these devices in a later
00:07:40 - Nugget, of course, but a device that is typical at the
00:07:45 - physical layer we no longer see in use today and it's a
00:07:48 - hub or a bit spitter or a repeater. 00:07:54 - That's right.
00:07:55 - In fact, I just thought of another one-- an extender.
00:07:59 - So hubs, often called repeaters or extenders, are
00:08:04 - going to be an example of something that works at the
00:08:06 - physical layer. 00:08:07 - They are not very sophisticated
at all. 00:08:10 - That's why I love the slang for
them of bit spitter. 00:08:13 - They're taking in bits, and they're
not doing anything 00:08:16 - sophisticated.
00:08:17 - They're just spitting those bits out.
00:08:22 - Now what about the data link layer? 00:08:24 - What the data link layer is going
to be obsessed with 00:08:28 - getting stuff ready for the physical
layer, and taking 00:08:32 - stuff off the physical layer and
moving it up the stack. 00:08:35 - One of the other important jobs
of the data link layer is 00:08:38 - to go ahead and start to do some
error correction, some 00:08:43 - error discovery, and it will attempt
to correct any errors 00:08:47 - that are discovered when stuff
is going on to the physical or 00:08:50 - from the physical layer.
00:08:52 - Pretty cool. 00:08:53 - At the data link layer, the devices
that are so 00:08:57 - unbelievably important today are
switches. 00:09:02 - Yeah, switches we are going to
be studying in this course 00:09:05 - quite a bit, specifically, the
Nexus. 00:09:08 - Yeah, the next generation powerhouse
switches that are 00:09:13 - available from Cisco.com.
00:09:16 - At the data link layer we have another important technology
00:09:19 - that's used in ethernet networks and
00:09:22 - that is a Mac address. 00:09:24 - Sure, I bet you've heard of this.
00:09:26 - And in fact, let's jump on to my PC right now and see an
00:09:31 - example of a layer two or data link layer address in my
00:09:37 - ethernet network called a Mac address. 00:09:40 - So here's the command prompt on
my Windows 7 machine. 00:09:43 - And if I go to this command prompt
and say IP config/all, 00:09:49 - we'll get all these great details
about my TCP/IP 00:09:53 - configuration on the system.
00:09:55 - Here is my wireless LAN adapter that's
00:09:58 - built into my laptop. 00:10:00 - And look at this, here is the physical
address. 00:10:04 - Let me go ahead and actually show
you that. 00:10:06 - Let me highlight it.
00:10:08 - So here is the wireless LAN adapter that I'm using, and
00:10:13 - here is the physical Mac address of
00:10:16 - that particular system. 00:10:18 - This is an important Layer 2 or
data link layer address 00:10:23 - that uniquely identifies my system
on 00:10:27 - that Layer 2 network.
00:10:29 - How cool? 00:10:30 - Now let me just warn you that these
Layer 2 addresses-- 00:10:34 - they're 48 bits in length presented
in hexadecimal 00:10:39 - characters but there will be variation
in how different 00:10:44 - computer systems will represent
them. 00:10:46 - So a Windows 7 machine does two
hex characters and a dash, 00:10:51 - two hex characters and a dash.
00:10:53 - In a Cisco environment, you might see four hex characters
00:10:57 - and a period. 00:10:59 - So just be ready for some flexibility
here in how the 00:11:02 - different devices will portray
them. 00:11:05 - Now by the way, before we leave
this focus for now on 00:11:09 - the data link layer, I want to
tell you about another data 00:11:12 - link layer device.
00:11:14 - And it's kind of legacy now. 00:11:16 - We don't see a much anymore but
they were bridges. 00:11:19 - Bridges predated switches, and
they were Layer 2 devices. 00:11:25 - And they would deal with Layer
2 addresses, but they were 00:11:29 - just really to bridge or adapt
one section of 00:11:33 - your network to another.
00:11:35 - Oftentimes, we might have one type of technology in this
00:11:38 - part of the network and we needed to bridge it to another
00:11:41 - type of technology in another part of the network.
00:11:46 - Now when you tell your friends and family that you are a data
00:11:50 - center network engineer they are going really be thinking
00:11:53 - about you in terms of Layer 3. 00:11:55 - That's right, the network layer
of the OSI model. 00:11:59 - This is where we have IP living,
yeah, the internet 00:12:03 - protocol, for instance.
00:12:04 - And we have those Layer 3 IP addresses. 00:12:08 - This is where devices called routers
are operating, right? 00:12:14 - And these routers in a data center
environment they're 00:12:19 - going to be very large devices.
00:12:22 - In fact, let's take a look at one now.
00:12:25 - Here is a 7700 series 18 slot Nexus. 00:12:33 - It's actually a switch, by the
way, but we refer to it in a 00:12:38 - multi-layer switch terminology.
00:12:42 - So I would call this a multi-layer switch.
00:12:45 - What does this mean? 00:12:46 - Well we know that a switch is at
Layer 2 of the OSI model, 00:12:50 - but because we say multi-layer,
this has the 00:12:53 - ability to do Layer 3 routing as
well. 00:12:57 - Look at this thing.
00:12:59 - Look at all those slots that are modular that would give
00:13:02 - you the ability to configure this router just the way you
00:13:07 - need it to be configured for your data center environment.
00:13:12 - Now when information is coming down from the application
00:13:16 - layer, or when information is going up the stack, it's the
00:13:21 - job of the transport layer to decide how this particular
00:13:26 - information will be transported. 00:13:29 - Now there's going to be two options
here, right? 00:13:33 - There's going to be to do this
reliably or unreliably. 00:13:40 - And sure enough, there were two
protocols that we'll focus 00:13:44 - on in this course that are going
to decide whether the 00:13:48 - information is transported reliably
or unreliably. 00:13:51 - And these are TCP, the transmission
control protocol 00:13:56 - for reliable communications and
UDP, the user datagram 00:14:01 - protocol for unreliable communications.
00:14:05 - I'll have a Nugget where I elaborate on both of these
00:14:09 - because I'm sure one of your questions right now is why in
00:14:12 - the world would I ever want to send something unreliably in
00:14:16 - the network? 00:14:17 - That just doesn't sound smart at
all. 00:14:20 - We'll answer that question and
many more when we look at 00:14:23 - those in much detail later on in
the series. 00:14:27 - Now next up in our stack we have
the session layer. 00:14:31 - The session layer is responsible
for just that, 00:14:35 - creating and managing and tearing
down sessions between 00:14:40 - communicating systems.
00:14:42 - Just think about one of the web servers up at Amazon.com.
00:14:46 - Think of how many different sessions are being initiated
00:14:50 - with that particular web server. 00:14:53 - I mean, it's mind boggling.
00:14:55 - And there needs to be a layer of the OSI model that's going
00:14:59 - to make sure that these sessions are properly managed.
00:15:04 - That's the job of Layer 5. 00:15:07 - Notice we're now while getting
into a discussion of those 00:15:10 - upper layers which we as data center
engineers aren't going 00:15:15 - to have all that direct involvement
with. 00:15:19 - At Layer 6, the presentation layer,
the obsession is 00:15:24 - formatting of the information that
comes down from the 00:15:27 - application layer so that machines
can readily read it. 00:15:31 - What would be a great example of
a presentation layer 00:15:34 - technology?
00:15:35 - How about JPG? 00:15:36 - Yeah.
00:15:37 - The standard for photos, for images on computer systems.
00:15:44 - So the presentation layer-- 00:15:46 - all about presenting the application
layer information. 00:15:51 - Pretty cool.
00:15:52 - Then finally, we have the application layer itself.
00:15:55 - Good old Layer 7. 00:15:57 - And you will often hear that layer
referred to as Layer 7, 00:16:01 - by the way.
00:16:02 - Layer 7 is all about the particular protocols that make
00:16:07 - networking applications function. 00:16:09 - Let me give you a classic example,
HTTP, hypertext 00:16:14 - transfer protocol.
00:16:16 - We know this is the protocol that makes our world wide web
00:16:20 - functions possible. 00:16:21 - Another one would be file transfer
protocol. 00:16:24 - This is a network protocol up at
Layer 7 that allows file 00:16:30 - transfer applications to work their
magic. 00:16:35 - Now when an application up at layer
7 has some data that 00:16:40 - it's going to send down the stack,
as that data-- 00:16:44 - let's draw that data as a little
rectangle here-- 00:16:47 - as that particular data moves down
the OSI stack to be 00:16:54 - placed on the physical wire or
a radio wave, in the case of 00:16:58 - wireless, as that chunk of data
moves down, we have 00:17:02 - process called encapsulation.
00:17:06 - And what's happening with encapsulation is each layer is
00:17:10 - placing some additional header information
00:17:14 - onto that data packet. 00:17:16 - So each one is adding some additional
information. 00:17:21 - We call these headers.
00:17:24 - And they are going to have important information about
00:17:28 - functions at that particular layer. 00:17:31 - You know what this reminds me of?
00:17:32 - It reminds me of when the CEO of a company calls in his
00:17:38 - assistant and he says I need to get this to Bill Gates
00:17:42 - right away. 00:17:43 - And he scribbles something down
on a piece of paper and 00:17:46 - hands that piece of paper to his
assistant. 00:17:49 - She then puts some information
on an envelope on that 00:17:53 - original communication.
00:17:54 - And she runs it down to the mail room and she hands it to
00:17:57 - a mail clerk. 00:17:58 - He puts it in another envelope
and puts some addressing 00:18:01 - information on.
00:18:02 - And then he goes to Federal Express and they put an
00:18:05 - envelope with additional information on.
00:18:08 - So that original communication from the CEO is at each layer
00:18:13 - of the communications getting additional addressing
00:18:16 - information so it can successfully reach its
00:18:20 - destination. 00:18:21 - This is the encapsulation process,
folks. 00:18:25 - And you know what, if we have information
at the destination 00:18:30 - moving up the stack, sure enough,
this additional 00:18:34 - information is going to be stripped
off as it moves up 00:18:38 - each layer.
00:18:39 - And this process is called de-encapsulation. 00:18:43 - So we have encapsulation and de-encapsulation
which are 00:18:47 - critical to network communications
taking place. 00:18:51 - Now when you are referring to the
information that the 00:18:54 - application layer sends down, we
have a chunk of stuff that 00:18:57 - we call data.
00:18:59 - Yeah, this is the data that we're interested in sending on
00:19:01 - the network. 00:19:02 - Now when we have some header information
and then the data, 00:19:06 - we call this a protocol data unit.
00:19:10 - That's right. 00:19:10 - This is how we refer to those headers
and the data itself. 00:19:15 - Now there are some names that we
give to the protocol data 00:19:19 - units at the lower four layers
of the OSI model. 00:19:23 - Remember, we said this is where
we're going to shine, 00:19:25 - this is where we're going to make
all our money? 00:19:33 - By the way, let's back up.
00:19:34 - Up here at the top, these top three layers, the data and the
00:19:41 - headers we tend to just kind of a lazily refer to all of
00:19:45 - that as just data. 00:19:46 - But then when we get to the transport
network data link in 00:19:51 - physical, these important lower
four layers that we're 00:19:54 - obsessed with, we give them nicknames.
00:19:57 - For instance at Layer 4, we call the headers
00:20:00 - and the data a segment. 00:20:02 - Yeah.
00:20:03 - At Layer 3, we call the headers and the data a packet.
00:20:09 - At Layer 2, we call the headers and the data a frame.
00:20:14 - And at Layer 1, we call all of that information bits.
00:20:19 - Now my friend Darren Dennis, years and years ago, back at a
00:20:23 - company called Knowledge Net where we worked together and
00:20:26 - trained online, he invented a great mnemonic for this.
00:20:30 - It's Some People Fear Birthdays. 00:20:37 - I don't.
00:20:38 - It's weird, but some people do. 00:20:40 - I don't know.
00:20:40 - Maybe they're afraid of the candles. 00:20:42 - So Some People Fear Birthdays is
an easy way we can remember 00:20:46 - segment, packet, frame, and bits.
00:20:49 - And boy oh boy, if you've been around my training for any
00:20:52 - amount of time, you'll know that I'm a big
00:20:54 - stickler about this. 00:20:56 - If you're talking to me about the
information that your 00:21:00 - Layer 3 is sending, you better
call it a packet. 00:21:03 - If you're talking to me about Layer
2 transport, you better 00:21:07 - call that information frames.
00:21:09 - Yeah, I'm really careful to use the correct terminology
00:21:13 - because after all, Layer 2 concerns are going to be quite
00:21:18 - different from Layer 3 concerns. 00:21:22 - Now there's another very important
point I want to make 00:21:24 - about this OSI model.
00:21:26 - And that is the fact that these layers are obviously
00:21:31 - helping each other, right? 00:21:32 - They're obviously going to be helping
each other. 00:21:35 - And what's interesting about this
is they are indeed 00:21:40 - unaware of each other though.
00:21:42 - For instance, the session layer on one machine thinks it
00:21:47 - is communicating directly with the session layer
00:21:51 - of the other machine. 00:21:52 - It's not really aware of or caring
about what's going on 00:21:56 - down here or up here.
00:21:59 - So the layers are communicating, in their
00:22:02 - opinion, with the opposite layer on the other machine.
00:22:07 - Pretty interesting and important fact.
00:22:10 - Now so many engineers out there think this all started
00:22:13 - with the OSI model but it actually didn't.
00:22:16 - There was a model invented by the Department of Defense in
00:22:20 - the United States in the '70s that predated the OSI model
00:22:25 - and it's called the TCP/IP model. 00:22:28 - Notice we need to master the four
simple layers of the 00:22:33 - TCP/IP model.
00:22:34 - And an easy way to do this and really a necessary thing for
00:22:38 - you to do is to correlate it to the OSI layers.
00:22:42 - Notice the data link layer and the physical layer simply
00:22:46 - become one layer called network access.
00:22:49 - The network layer is termed the internet layer.
00:22:53 - The transport layer is just the same and it's in the same
00:22:58 - relative location in the stack. 00:23:00 - And then the application, presentation,
and session 00:23:04 - layers are simply the application
layer in the 00:23:08 - TCP/IP model.
00:23:09 - So understand and memorize these four simple layers, and
00:23:15 - please be able to coordinate them to the OSI.
00:23:18 - For instance, hey, I know there's a network access layer
00:23:22 - and it incorporates the data link player and
00:23:25 - the physical layer. 00:23:26 - This might be a great time where
you should start making 00:23:29 - some flash cards if you haven't
already, either 00:23:33 - traditional paper based flash cards--
00:23:35 - I like to have the muscle memory of writing down
00:23:38 - information-- 00:23:39 - or maybe you're fancier and you
like 00:23:41 - electronic flash cards.
00:23:43 - Whatever it is, now might be a good time to start because
00:23:46 - we're already seeing the massive amount of memorization
00:23:50 - we need to succeed as a CCNA data center.
00:23:55 - Now for time to time at the end our Nuggets, we'll have a
00:23:58 - little fun with Exam Time! 00:24:00 - Yeah, you remember MC Hammer and
Hammer Time? 00:24:04 - This is Exam Time!
00:24:05 - And our theme song is [SINGING], enough of that.
00:24:10 - So anyways, it's exam time. 00:24:12 - And we're going to take a quick
one here. 00:24:14 - What device operates at Layer 2
of the OSI? 00:24:18 - And notice in your exam in the
actual exam, Cisco will be 00:24:23 - real great about pointing out to
you how many correct 00:24:27 - answers there are.
00:24:28 - If they don't mention this choose whatever, it's just one
00:24:32 - correct answer, but if they mention it's choose two,
00:24:34 - choose three, then obviously, we have to select that many
00:24:37 - correct answers. 00:24:39 - So what is it, folks?
00:24:40 - What device operates at Layer 2 of the OSI model?
00:24:43 - Is it a hub? 00:24:44 - Is it a switch?
00:24:45 - Is it a bridge? 00:24:46 - Or is it a router?
00:24:48 - Well we indicated that switches are the Layer 2
00:24:53 - devices of our modern data center and we just love them
00:24:56 - so we'll elaborate on them in great detail on this series.
00:25:01 - And we said that bridges predate those switches so
00:25:05 - that's another Layer 2 technology. 00:25:07 - So our correct answers are b and
c in this particular Exam 00:25:12 - Time break.
00:25:15 - By the way, if you're interested in a full practice
00:25:19 - exam, we'll do a lot of questions together throughout
00:25:22 - the Nugget series to give you confidence and to discuss the
00:25:26 - types of questions you'll face. 00:25:28 - But if you're interested in a really
excellent full blown 00:25:31 - practice exam for this particular
test, just go up to 00:25:35 - Amazon.com and put in the test
number 640-911. 00:25:40 - And you will see on the first page,
you will see an awesome 00:25:45 - practice exam from my good friend
Kevin Wallace over at 00:25:49 - OneExamamonth.com.
00:25:52 - This is the practice exam that I used and I swear by it.
00:25:56 - It was superb. 00:25:57 - And I achieved first time attempt
success with this 00:26:02 - particular exam.
00:26:03 - Notice it's a nice ebook with a nice price tag.
00:26:08 - So check it out up at Amazon.com, and again, I found
00:26:11 - that by just doing 640-911 as a search.
00:26:16 - So congratulations. 00:26:18 - You've enjoyed the first Nugget
of our CCNA data center 00:26:22 - series in which we took a look
at the why and the what behind 00:26:27 - the OSI model.
00:26:29 - We also examined the TCP/IP model which predated this
00:26:34 - important model. 00:26:35 - And we know that we need to be
able to correlate the OSI 00:26:39 - model with the early TCP/IP model.
00:26:43 - Well I hope this has been informative for you.
00:26:45 - And I'd like to thank you for viewing.