-: The TCP/IP model. 2 2
Now, if you remember all the way back out 3 3
when I started talking about the OSI model, 4 4
we mentioned that the OSI model was a reference model, 5 5
but it wasn't the only reference model out there. 6 6
And the other one that we're going to talk about 7 7
is known as the TCP/IP model. 8 8
This is also called the TCP/IP stack or the DoD model 9 9
named for the Department of Defense who created it. 10 10
Now, the TCP/IP model is an alternative to the OSI model. 11 11
And the nice thing is it's actually only four layers 12 12
instead of the seven layers of our OSI model. 13 13
This is going to make it a little bit easier 14 14
for most people to understand. 15 15
And it's also easier for us to learn this model. 16 16
Now, it's also going to be a little bit more relevant 17 17
than the OSI model today 18 18
because almost all computer networks these days 19 19
are TCP/IP-based 20 20
and the TCP/IP model refers specifically 21 21
to those four layers and how things work 22 22
in today's modern networks. 23 23
Whereas the OSI model is going to sometimes 24 24
be a little bit more blurry as you're trying to force things 25 25
into those seven individual layers. 26 26
So how does the OSI model compare to the TCP/IP model? 27 27
Well, I already mentioned that there's four layers in one 28 28
and seven and the other. 29 29
Let's take a look at that. 30 30
So how exactly does the OSI model compare 31 31
to the TCP/IP model? 32 32
Well, it's actually pretty simple. 33 33
If I take layers five, six, and seven from the OSI model, 34 34
those top three layers, and I smash them all together, 35 35
I get something known as the application layer 36 36
inside the TCP/IP model. 37 37
Now, the application layer here 38 38
is going to contain application, presentation and session, 39 39
all of those OSI model functions, 40 40
into a single layer called the application layer 41 41
under the TCP/IP model. 42 42
Next, we have the transport layer from the OSI model, 43 43
and this one is really easy 44 44
because we're just going to take it and move it right in 45 45
to the TCP/IP model. 46 46
Everything the way that it was in the OSI model 47 47
still applies here. 48 48
Next, we get down to the network layer of the OSI model. 49 49
Here, we're going to take this layer 50 50
and move it straight over to the TCP/IP model as well. 51 51
But when we do that, we're going to change its name. 52 52
Instead of calling it the network layer under the OSI model, 53 53
we're going to call it the internet layer 54 54
inside the TCP/IP model, 55 55
because it really is all about routing things externally, 56 56
either to or from the internet, from within our networks. 57 57
Then we have our final two layers 58 58
at the bottom of the OSI model. 59 59
This is our data link and our physical layers. 60 60
These two layers are going to be combined 61 61
under the TCP/IP model 62 62
and called the network interface layer 63 63
because this is how our users are going to interface 64 64
with our networks and connect to them. 65 65
So as you can see, this is pretty simple 66 66
when you start looking at the OSI model 67 67
versus the TCP/IP model in this way. 68 68
You basically take the top three layers 69 69
and you squish them all together. 70 70
And this gives you the application layer. 71 71
You take those bottom two layers 72 72
and you squish those together 73 73
and you move them over into the TCP/IP model. 74 74
And that's how you go from seven layers of the OSI model, 75 75
into the four layers of the TCP/IP model, 76 76
by making sure you squish those top three 77 77
and squish those bottom two layers together. 78 78
Now, for the exam, you need to understand the TCP/IP model 79 79
and it's layers. 80 80
So if you can draw this diagram, you're going to be covered 81 81
because you already know 82 82
everything else you're going to need for test. 83 83
See, what we're dealing with here 84 84
is knowing what those seven layers are of the OSI model 85 85
and how they represent themselves inside the four layers 86 86
of the TCP/IP model. 87 87
We already learned all about those seven layers individually 88 88
in the OSI model. 89 89
So that knowledge is going to carry over too. 90 90
Now, let's take a quick look at these four layers 91 91
in the TCP/IP model as a review from our days 92 92
using the OSI model. 93 93
First, starting at the bottom, 94 94
we have the network interface layer. 95 95
This is layer one. 96 96
And it's all about physical and electrical characteristics, 97 97
just like in the OSI model. 98 98
Now here, we're going to describe 99 99
how we're going to transmit bits across our networks, 100 100
those ones and zeros that we had in our physical layer. 101 101
It's also going to determine 102 102
which type of network medium we're going to use. 103 103
Are we going to be using twisted pair copper cabling, 104 104
coaxial cable, fiber optic cable? 105 105
What do we want to use here? 106 106
Maybe we're going to use wireless. 107 107
Are we going to run TCP over ethernet 108 108
or are we going to use token ring, serial, 109 109
or some other type of network? 110 110
All of this gets put together 111 111
inside our network interface layer. 112 112
The second layer we have is known as the internet layer 113 113
inside the TCP/IP model. 114 114
This is where we take data and package it 115 115
into those IP datagrams, 116 116
just like we did with layer three of the OSI model of four. 117 117
Now, it's going to contain your source 118 118
and your destination IPs, 119 119
and it's going to forward those datagrams 120 120
between different hosts across the networks. 121 121
These data grams 122 122
are going to be pushed around the networks through routing, 123 123
and we're going to use our routers to do this. 124 124
And this connectivity is usually going to occur 125 125
externally from your network to some remote network. 126 126
This is where your internet is going to get connected 127 127
to the intranet. 128 128
This is internal versus external. 129 129
Now, examples of the internet layer and TCP/IP 130 130
include things like IP, ICMP, ARP, and Reverse ARP. 131 131
And we're going to talk all about these things in more depth 132 132
as we go through switching and routing 133 133
later on in this course. 134 134
Now, I understand I just threw a bunch of acronyms at you, 135 135
but I promise I'm going to come back to them later 136 136
and I'm going to teach you all about them. 137 137
So don't worry about them yet. 138 138
Next, we have our third layer. 139 139
This is the transport layer, 140 140
and it's exactly the same as the transport layer 141 141
in the OSI model. 142 142
It's going to define the level of service 143 143
and the status of the connection being used by TCP, 144 144
UDP, or RTP. 145 145
TCP is our connection full protocol. 146 146
UDP is our connectionless protocol, 147 147
and RTP is our real-time protocol, 148 148
which is normally used for streaming voice and video. 149 149
The fourth and final layer of the TCP/IP model 150 150
is the application layer. 151 151
And this is going to combine the top three layers 152 152
of the OSI model into a single layer 153 153
to define the application protocol 154 154
that we're going to be using. 155 155
This is also going to dictate how the programs 156 156
are going to interface with the transport layer 157 157
by conducting session management. 158 158
And it's going to be the layer 159 159
where the user is going to interact with the network 160 160
through some sort of program. 161 161
Examples of this come from layers five, six, and seven 162 162
of the OSI model, 163 163
again, because we squished all three of those down 164 164
into this one application layer. 165 165
This would be things like the Hypertext Transfer Protocol 166 166
for web browsing, Telnet for remote control, 167 167
FTP for file transfer, SSH for remote shell, 168 168
SNMP for network management, 169 169
DNS for domain name resolution, SMTP for sending mail, 170 170
an SSL or TLS for secure web browsing and encryption. 171 171
All of these things are going to be found here 172 172
in the application layer of the TCP/IP model. 173 173
All right. 174 174
So what are we going to cover in this section of the course? 175 175
Well, we're going to be focused again 176 176
on domain one, networking fundamentals, 177 177
and we're going to cover objectives 1.1 and 1.5. 178 178
Objective 1.1 says that you must be able to compare 179 179
and contrast the OSI model layers 180 180
and encapsulation concepts. 181 181
Objective 1.5 states that you must be able to explain 182 182
common ports and protocols, 183 183
their applications and encrypted alternatives. 184 184
We're also going to briefly dive into domain five, 185 185
network troubleshooting, by returning to objective 5.3. 186 186
Objective 5.3 states that given a scenario, you need to use 187 187
the appropriate network software tools and commands. 188 188
So in this section, 189 189
we're specifically going to be doing some hands-on work 190 190
with Nmap, the network mapper tool, 191 191
to show you how this works. 192 192
All right, let's get started talking all about ports 193 193
and protocols using the TCP/IP model 194 194
in this section of the course.