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OSI is one of those things where you ask three different network engineers what layer something is in and you'll get six different answers.
In my years of experience it's always been another one of those need it for the test and forget it type of things, mainly because as you've shown, the layers kind of blend into each other.
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Here's why I think the OSI Model is useful.
If we can logically predict the behavior of a network as a packet goes from here to there, I'm better able to troubleshoot a problem.
In the online class that I'm taking, we're using a program that functions like WireShark and we have to send a ping across the network and list all the paths it's gonna take before we send the ping. Because I'm able to predict the exact path using the OSI model, I able to better find a problem should the network break down.
The OSI Model is all theory...until you view it on WireShark and then it becomes reality.
I just watched a 1.5 hour lecture on the OSI model. Before I comment on that let me preface what I'm about to say.
Before I understood subnetting, I HATED it. When I was in school for electronics many years go and was learning about AC being superimposed on DC, I HATED it. Likewise, when I was learning about the OSI model, I HATED it. It's human nature to hate something that we don't understand. Especially if it's really difficult to grasp.
As much as I HATED all of those things while I was trying to learn them, I love all of them now that I understand them. When it comes to the OSI Model, I love it so much that I have my own favorite layer - Layer 4. I think it's the most confusing layer and thus I spent more time learning it. So, I have more investment in Layer 4. I guess that's why I love it the most.
When I was learning subnetting, I was told that learning subnetting was a thing of the past and that there's calculators for that now. It's true that there are calculators for that. But does that mean that learning subnetting was a waste of my time? The answer is no. There were many valuable lessons that I learned. Things that I was completely in the dark about was brought into light. Because I learned subnetting, when I look at an IP address or a subnet, I know what they represent. That's a big deal.
The same holds true for the OSI Model. 3 days ago, I thought I understood the OSI model. The truth is that I didn't understand it at all. AT ALL. Now that I do understand it, things that I was completely in the dark on have been brought into the light.
You want to understand ports? Learn the OSI model. Want to know about IP addresses? Lean the OSI Model. Want to know about MAC addresses? Learn the OSI model. What to know how they all tie together? Learn the OSI Model. Want to learn how to use WireShark and actually understand it? Learn the OSI Model.
Last but not least, we've all heard about TCP/IP. Those are 2 totally different things that I won't get into. How do I know this? Because I learned the OSI Model.
Last edited by BillyCarpenter; 04-16-2021 at 02:07 PM.
Since I bought up TCP/IP, I guess I'll explain it.
TCP is a protocol that performs segmenting. It takes a large group of data and breaks it into smaller segments. A the beginning of each segment, there's a header that is applied in order for the data to be reassembled. Without the added header, the data couldn't be put back together on the other end. This all happens on Layer 4. But there are other protocols used at Layer 4. TCP and UDP are the most common.
IP is found at layer 3 and is nothing like TCP. IP does no segmenting. IP applies another header with the source and destination IP address that is used to route the data to the correct network.
Let's not stop there....
Layer 3 only gets the data to the correct network. We still need to get the data to the correct device. That's where layer 2 comes in at. Layer 2 is the Data Link Layer and deals with MAC addresses. That gets the data to the correct device.
Last edited by BillyCarpenter; 04-16-2021 at 01:43 PM.
I said that Layer 4 is may favorite layer. It's also the most difficult to learn, in my humble opinion.
One of the things that happens at layer 4 is the ports for the host PC and client PC are chosen. How does this work? Let's say that my PC (client PC) wants to access Amazon.com (host PC). My operating system (windows 10) is gonna randomly select a port between the range of 1024 to 49151. That's gonna be the port on my PC that connects to the server on Amazon.com. However, the destination port to Amazon.com will NOT be chosen randomly. All HTTP sites will connect on Port 80. How does my PC know to connect to port 80 on Amazon's server? That is all done by programmers that created Amazon's website. And If I click on "Pay Now" on their website, a new port connection will be made on their server at Port 443 - (HTTPS port).
PS - All of the different ports that are available are the reason we can open 10 different websites at one time. Think of it as multiplexing.
I decided to come up for air and give an update on my training.
It's crazy stuff. But first things first. When I signed up for CBT Nuggets online course, I had heard good things about them. Don't go there. Luckily I was able to cancel within the first 7 days. Too much bullshit that has nothing to do with learning about networking. Too much joking around. Too much personality. If I want jokes, I'll go to a comedy club.
I signed up for a different online course and it's fantastic. But I will say that this stuff is hard. Next level hard. There are times that I question my sanity.
At the moment I'm learning how to trace packets thru a network and watching as packets are encapsulated and decapsulated. Think WireShark. The best way that I can describe it is it's like trying to understand encryption...not that I know anything about that. It's just what I imagine. I'm getting better and better at it, though. It seems impossible at first.
Back to the grindstone.
What a surprise
There's a stark contrast between the training course I'm taking now and the one that I was taking before. An old saying comes to mind: “Tell me and I forget, teach me and I may remember, involve me and I learn.”- Ben Franklin.
You have come far, Grasshopper.Originally Posted by BillyCarpenter
“I think you should treat good friends like a fine wine. That’s why I keep mine locked up in the basement.” - Tim Hawkins
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