BackLaying the keel, a Layered Approach
Saar here, resident engineer at Myriad Supply. Today I’ll be discussing the OSI Model and the 7 layers.
1) Firewalls:
a. Basic
b. Next Generation
c. Application Layer firewalls- Palo Alto/ Juniper
d. Web application Firewalls- Mykonos now rebranded to webapp secure firewall
Let’s review some basics about the OSI model and the 7 layers:
The first layer is physical. This is the cabling- either copper, fiber, or radio. The is very simple to grasp as it’s prett much the same as the telegraph. One device will send 0 or 1 or a BIT. 0 means no power, and 1 means power. To send, the device goes “11111111”, which tells the other side to be ready and start counting. Then, it will send. This the alphabet has 26 letters:
To send the word “Myriad” you would need to send: 13,25,18,9,1,4. Because we only have a 0 and a 1, we have to come up with a way to do this. For that, computers use BINARY. In binary, we set a value to each place.
So I will send you 5 bits: 11111111- bit 1 , bit 2 , bit 3 , bit 4 , bit 5 – 11111111. The 1111111 is used to start and finish or get ready to listen, for example.
If I want to send 13, I will send:
Bit 1 = electricity or 1
Bit 2 = no electricity or 0
Bit 3 = electricity or 1
Bit 4 = electricity or 1
Bit 5 = no electricity or 0.
You can now add them up- They will be 1 + 4 + 8 = 13.
A lot of work to send for 13 but for PCs today it’s barely a nano-second. That is pretty much it at layer 1. All the devices do is simply push bit.
a 3750 switch with a 1000 MBps port can push 1000 million bits per second. That would be like saying Myriad 2,000,000 times or so!
When I started with the internet, the devices could push 10 million bits per second (10 MBPS), then 100 MBPS. Today it’s 1000 Mbps. Myriad sells 10,000 Mbps or 10 Gbps, 40 Gbps, and even 100 Gbps. Notice how fast progress is.
Now a layer 1 device is simply a connection from point A to point B.
The bigger the Mbps or Gbps the more 1s and 0s you can push per second.
Layer 2:
Okay. I’m in New York, smoking my cigar, managing my train company.
I want to send a message to San Francisco asking them of the boat with my fine China set for my Mrs. has arrived. (Side note: In general when you send electricity on a wire, the copper has friction. With every mile, you get less and less signal and eventually it dissolves and you can not tell if there is a signal- similar to yelling).
So what they did was put a telegraph station at each location or intersection.
This is pretty much a SWITCh. The location would get a message, that would say “TO: San Francisco Message: How is my wife’s china doing? Is it here yet? -Boss”
So station 1 in Kentucky would get the message and imply repeat it towards Missouri. Missouri would repeat it to Colorado , and Colorado would send it to San Francisco. That’s pretty much what a switch does. It takes a message that comes in on port 1 (New York Cable), looks in its cable, and sends it to port 2 (Colorado). 
In the IT world, we do this using something called a MAC address. The MAC address for each device in the world is UNIQUE. If you click start, then run, then type command, you will see yours. Simply type ipconfig/all.
So let’s recap: ever network card manufactured in the world has a unique MAC address. Each vendor gets a unique code for the first part. The second part is the number of the card.
So that’s layer 2. Let’s say I want you to tell me your MAC addres so I can send you a message. The only problem is that there are 1,0000000000000000000000000000000000000000 users on the web, so my switch need to have a table with 1,0000000000000000000000000000000000000000 lines, which is unrealistic.
The solution: Layer 3:
It condenses that table and uses IP addresses. How does it work?
A company will apply for an IP address. Xerox, for example, is 13.0.0.0 to 13.255.255.255. IBM is 9.0.0.0 to 9.255.255.255 (check yours out at http://www.ipchicken.com/). What they did was assign Number 1-100 to the USA, 200-500 to Europe, and 200-250 to England (in Europe). The routers now have smaller tables. So if the number is between 200-500, send it to Europe. Once it arrives in Europe, the router has some more lines. So if 200-250, send to England. 250-300 send to France, etc. As you can see, this minimizes the size of the tables on the internet. Routers and layer 3 switches use IPs to know where to send the data.
In order to synchronize the tables and the changes around the world, they use ROUTING protocols. So now to send something to Myriad Supply, you simply look up their address. 
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Since Myriad’s server has multiple things running on it, and we only have one server, how can I tell the server which one I want to connect to? Enter, Layer 4:
Layer 4 uses ports. You simply say which port on the server you want to connect to.
25: 23.23.214.129 = Mail
Stay tuned on layers 5 and 6, which we will skip for now.
Layer 7: So after I connected- 25: 23.23.214.129 EMAIL, I can start talking in the APPLICATION called Email, or, in our case, Exchange. Once I locate the port for WEB, I can surf the Myriad web server, which is an application.
And, Voila!
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Saar Harel is a resident Engineer at Myriad Supply, and has been in the Networking Field for over 20 years. You can check out his Google+ and ask him questions!
