Need some advice on learning networking

[dickierock]

Re: Need some advice on learning networking

I did CCNA a couple of years ago, and probably have the most of it forgotten .
Subnetting is handy to know in terms of installing copiers, but really if your installing in locations with large networks and subnets, then the i.p. addressing should be provided for you by the I.T. dept.

Anyways, I found this guy on Jermey's I.T. Labs on Youtube very helpful, just for the sheer simplicity of the way he explains his labs.
Jeremy's IT Lab - YouTube

Best of luck with it.

[BillyCarpenter]

Re: Need some advice on learning networking

I did CCNA a couple of years ago, and probably have the most of it forgotten .
Subnetting is handy to know in terms of installing copiers, but really if your installing in locations with large networks and subnets, then the i.p. addressing should be provided for you by the I.T. dept.

Anyways, I found this guy on Jermey's I.T. Labs on Youtube very helpful, just for the sheer simplicity of the way he explains his labs.
Jeremy's IT Lab - YouTube

Best of luck with it.

Congrats on getting your CCNA. I hope to get there with a little luck. Take care.

[BillyCarpenter]

Re: Need some advice on learning networking

This has gotten really deep BUT I'm starting to grasp the concept of frames and packets and how they traverse the network.


It was easy for me to understand frames and packets as they relate to a switch. Much more difficult when dealing with a router.


Here was my breakthrough moment and when it started to make sense.


What I failed to understand is that every port on a router represents a different network. So, if a router has Port fa 0/0, fa 0/1 and gig 0/0...that's 3 separate networks. Also, each one of those ports have their on MAC address that is burned in from the manufacturer. And each port has it's own IP address that I assigned to it.

There's much more to it that I could explain but it's complicated and we'll leave it at that.

[BillyCarpenter]

Re: Need some advice on learning networking

I like to explain what I learned on here because explaining it to someone helps me to know that I have it down and it helps me to retain the information.

I'm studying the OSI model. Let's see if I can explain it. By the way, I encourage folks to point out any mistakes that I make in this thread. That would be doing me a favor.


Before I get into the OSI model, it should be noted that Layers 5, 6 and 7 are application layers and not much of a concern for a networker. But you do need to know a little something about them. At least for the test.


Layer 7 - This is the actual data that we see on our screen from a website, for example.

Layer 6 - The data is formatted at this layer.

Layer 5 - Establishes a connection with website or server. Also responsible for ending the connection.


Here's where the fun happens:

Layer 4 - Provides transfer of data between end users. The application layer will dictate what protocol will be used. 99% of the time it will be TCP or UDP. TCP cares about reliability, UDP does not...for the most part. I'll throw in one bit of interesting information:
HTTPS is a TCP based application that uses SSL and has a well known port number: 443. Key fact: port numbers 1024 and lower are considered "well known" and are not to be used by end users. In fact, those ports are registered by the powers that be. Our PC's uses any port above 1024. Those ports are dynamically selected by Windows on my computer.

To sum it up, when you go to a website that uses HTTPS and go to a website like Amazon.com, Amazon's servers will be listening on port 443 for any requests. Our windows PC will pick a random port number on our PC that must be above 1024 to establish a connection with port 443 on Amazon's server.

Layer 3 - Adds the source and destination IP addresses.

Layer 2 - Fills in the source and destination MAC Addresses.

Layer 1 - The is anything that is physical on the network: cables, NIC, switches, ect.

[BillyCarpenter]

Re: Need some advice on learning networking

See all that stuff that I posted about the OSI Model? It's all true. And it's all a bunch of horseshit.

Allow me to explain. My explanation was all a bunch of stuff that I memorized and repeated. In the real world, it doesn't mean a damn thing because I didn't understand it. I've heard it repeated over and over so many times I just took it as the gospel. It's not. What I posted was only a guideline and nothing more.

In order for the OSI Model to do you any good in the real world of networking, we must go much deeper and actually understand it. I think I've done that and will attempt to explain it once again.

I'm gonna combine Layers 7, 6, and 5. They are all application layers and there's nothing we can do about them. This is a purely logical layer that was written by programmers. Here's the ONLY thing you need to know: Before the data gets passed down to the Transport Layer, it must be converted into binary format. At layer 7 is was in binary form but it was followed by .exe, jpeg, ect. Those must be stripped away before going to the Transport Layers.

Now the data is dropped down to Layer 4. It's at this layer that a segment will get added to the data. This segment contains the source and destination ports. The ports are predetermined by by the application from Layer 7. Example: If Layer 7 contained data that was HTTP, the port address would be 80. HTTP with SSL would be 443. You get the picture. At this point we're dealing with a segment at Layer 4.

Once the segment is dropped down to Layer 3, it will form a packet. We'll still have all the data from Layer 4 but a source and destination IP address will be added here at Layer 3.

Now the data is dropped down to Layer 2 - Data Link Layer. We still have all the data from Layer 3 and now a source and destination Mac address will be added.

And finally the data is transmitted across wires or fiber and that forms Layer 1.


The segments, packets, and frame are what make communication across a network possible and I think understanding the OSI model helps. At least in my mind.

[rthonpm]

Re: Need some advice on learning networking

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.

Sent from my BlackBerry using Tapatalk

[BillyCarpenter]

Re: Need some advice on learning networking

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.

[BillyCarpenter]

Re: Need some advice on learning networking

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.

[BillyCarpenter]

Re: Need some advice on learning networking

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.

[BillyCarpenter]

Re: Need some advice on learning networking

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.

[BillyCarpenter]

Re: Need some advice on learning networking

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.

[bsm2]

Re: Need some advice on learning networking

What a surprise

[BillyCarpenter]

Re: Need some advice on learning networking

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:

[bsm2]

Re: Need some advice on learning networking

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[KenB]

Re: Need some advice on learning networking

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.

You have come far, Grasshopper.