EPTI've never made a blog before, so I decided that while waiting for my friend to get home, I'd depart some knowledge up in here. This is my first blog, so of course, be extremely critical of content and style, please!
Introduction;
What is networking?
Simply put, a computer network is a connection between two end devices (PCs, laptops, VoIP phones, etc.) that can be as simple as one cable and as complicated as the Internet. For the purposes of learning, the Internet (contrary to expectations) is rarely studied. We'll focus on smaller networks where we have full control over everything in our network - no troublesome ISPs, no addressing requirements, etc. This might all sound like a foreign language now, but don't worry. By the end of this post, you'll have designed and built a working network capable of data transfer between end hosts!
To begin, download Packet Tracer 5 from here.
Packet Tracer is a networking simulator that allows for electronic simulation of network design and programming. It's super spiffy, and this the is most up-to-date version!
![[image loading]](http://b.vimeocdn.com/ts/676/985/6769850_640.jpg)
The OSI Model and Why It's Important;
The Open Systems Interconnection Model is a theoretical model of how networks function.
![[image loading]](http://baluinfo.com/wp-content/uploads/2010/06/osi-model-.gif)
It consists of seven layers; Application - Presentation - Session - Transport - Network - Data Link - Physical. Or rather, All People Seem To Need Data Processing!
Within the context of networking, it's important to understand the life cycle of a 'data' sent from one end device (host) to another host. As you can see, as a 'data' (referred to as a PDU from here on out) moves from one layer to another, more data is added to it. This data is a form of overhead - data separate from the PDU but necessary for travel through a network. The process of wrapping PDUs inside overhead is called encapsulation, and the process of taking overhead off of PDUs is called decapsulation.
What is added at each layer?
Well, for learning purposes, we'll study the second, third, and fourth layers - from the bottom, that's Data Link, Network, and Transport. The Transport Layer effectively records the source and destination port of the PDU. On Layer 4, a port refers to a software-based gateway for application or service specific traffic. Think of unblocking ports to play BW!
The Network Layer records the source and destination IP address. This is exactly what is sounds like! The IP address of your machine is responsible for most of it's networking hoopla!
The Data Link Layer records the source and destination MAC address. The MAC address is the unique address of your computer's physical network card and is like a fingerprint. It's used for communication where switching (decisions based on MAC) is used instead of routing (decisions based on IP).
Getting Used to Packet Tracer
![[image loading]](http://i.imgur.com/wG9lB.png)
Really quick!
The red box is where you can switch between what shows up in the blue box! It has different networking device archetypes and connections for cabling between devices.
The blue box obviously is where the different types of networking devices are.
The green box is your workspace!
The purple box contains the ribbon - it's fairly intuitive!
The orange box contains cursor options in order; Select, Move Layout, Add Text, Delete, Inspect, Resize Shape, Add Simple PDU, Add Complex PDU.
The pink box switches between simulation and realtime mode. We will eventually switch to simulation mode!
BUILDING YOUR FIRST NETWORK
Our first network consists of three PCs, two switches, and one router.
Switches are layer two devices that make decisions based on MAC addresses.
Routers are layer three devices that make decisions based on IP addresses.
Place devices as shown. Use 1841 routers and 2960-24TT switches. The model of switch determines the available interfaces.
Cabling in networking is simple.
Use straight-through cable when connecting devices on different layers.
Use crossover cable when connecting devices on the same layers, or when directly connecting PC to Router.
Use the same interfaces as shown. An interface is the physical port on a machine. Think of the "ethernet port" behind your machine! That's exactly what the "Fast Ethernet" ports are!
But why is the connection between the switch and the router red?
Because router interfaces are shut down by default. Click on the router to open it, and open the config tab. Click into interface FastEthernet0/0. Click on, and type in this IP address:
192.168.1.1
And this subnet mask:
255.255.255.0
![[image loading]](http://i.imgur.com/LYfe7.png)
Go ahead and exit the Router.
Now open the PCs by clicking on them. Navigate to the Desktop, then IP Configuration, then add the following information for PC0.
IP: 192.168.1.2
SM: 255.255.255.0
DG: 192.168.1.1
And then for PC1.
IP: 192.168.1.3
SM: 255.255.255.0
DG: 192.168.1.1
And finally, for PC2.
IP: 192.168.1.4
SM: 255.255.255.0
DG: 192.168.1.1
Recall that switches do not work with IP, but MAC, so they do not get addressing information.
Once your configuration is finished, CLICK ON THE STOPWATCH IN THE BOTTOM RIGHT TO ENTER SIMULATION MODE.
Zoom out so you can see your network.
Click on "Add PDU" (the envelope on the right), click PC0, then click PC2.
Click on Capture/Forward to view the PDU's journey through the network!
If the PDU moves from PC0 to Switch0 to Switch1 to PC2 to Switch1 to Switch0 to PC0, CONGRATULATIONS!
You have just made your first network!
The configuration steps should have gone over your head, at this point. In a follow-up, we will later explore why what we did did what it did!
Commentary on Part One and Discussion About Part Two:
+ Show Spoiler +
First, thanks for reading. I hope you really got something out of this. Secondly, if this is appreciated, there's the eventual part two, where I plan to go into more detail about IP addressing and why the network we made works!
5/5 from me
