Need some advice on learning networking

[BillyCarpenter]

Re: Need some advice on learning networking

Here's a fun little fact:


Ever wonder what happens when you sit down at your PC and try to contact a file server on your network or maybe you're trying to contact google.com? Where does the routing process first begin? How does it all get started?


Answer: The first place it starts is at your PC. More specifially, it starts by your PC looking at it's ARP TABLE to determine if you're trying to access something within your broadcast domain or something outside of your broadcast domain. If you're trying to access something on your network, a router isn't needed and the switch is all you need to contact your local file server. However, if you're trying to access google.com, your PC will need to connect to the gateway of your router. But it all starts with your PC's ARP TABLE.


Edit: To break it down further, your PC looks at it's own subnet. if you're trying to connect to something outside your network (subnet), you PC knows it must contact your router. If you're only trying to connect to a device that's within your subnet, the switch can do that by itself. You can take your router and throw it away and you'll still be able to connect with any device on your local network.

[BillyCarpenter]

Re: Need some advice on learning networking

Here's a question if anyone wants to take a crack at it. Let me preface the question first:

It is often said that switches don't care about IP addresses, they only care about MAC addresses. And it's often said that routers only care about IP addresses, they don't care about MAC addresses. With me so far?

Question: If a router doesn't care about a MAC address, then why do routers have a MAC address for each one of their ports?


Think about that hard and give me your answer.

[tsbservice]

Re: Need some advice on learning networking

After getting a look at the practice exam for the CCNA exam, it was clear that I needed to redouble my efforts on learning the OSI model. In fact, I knew I had to master the OSI model and there could be no gray area.


I read more. I watched more videos. I consumed any information that I could find.

I ran across an interesting case study of a real world problem and how using the OSI model helped find the solution.

A company had recently purchased some new software but it wasn't working across the entire network. The problem stumped the IT department and as a last resort, they decided to use a data analyzer (WireShark) to help identify the problem. We need to keep this in mind about "software." Software resides on Layer 7 of the OSI model. But that's only part of the story. Ultimately this software is what determines what ports are to be used. It's gonna determine what protocol is used at layer 4 - UPD or TCP? So, if there's a bug in the software, the data could end up being sent to the wrong port. There's only one way that I know of to troubleshoot this problem and that is to capture the data using a program like WireShark. But you're not gonna understand Wireshark unless you thoroughly have mastered the OSI Model.

Personally, I didn't pay enough attention to the application layer and that was a mistake.

I think any kind of reliable software should came with some manuals and what ports need to be opened to work.

[BillyCarpenter]

Re: Need some advice on learning networking

I think any kind of reliable software should came with some manuals and what ports need to be opened to work.

The problem wasn't that the manual didn't list the ports that needed to be opened. They did. The problem was that they made a mistake writing the software, thus it didn't matter what port you opened...it still wouldn't work.

[BillyCarpenter]

Re: Need some advice on learning networking

The problem wasn't that the manual didn't list the ports that needed to be opened. They did. The problem was that they made a mistake writing the software, thus it didn't matter what port you opened...it still wouldn't work.

Just to go a little deeper on this subject....

Software resides on layer 7 of the OSI model. When I say software, I'm not talking about google.com, or YouTube or anything like that. Software is gonna fall into one or more of several categories: HTTP, HTTPS, POP. SMTP, ect. Depending on what category the "software" falls into is gonna determine what port needs to be opened. In conclusion, if the software has a bug, you can open the correct port but it's not gonna work. Make sense?

[BillyCarpenter]

Re: Need some advice on learning networking

Here's a question if anyone wants to take a crack at it. Let me preface the question first:

It is often said that switches don't care about IP addresses, they only care about MAC addresses. And it's often said that routers only care about IP addresses, they don't care about MAC addresses. With me so far?

Question: If a router doesn't care about a MAC address, then why do routers have a MAC address for each one of their ports?


Think about that hard and give me your answer.

Here's the answer to the question: It's true that a router doesn't care about a MAC address nor does a switch care about an IP address.

So why do routers have MAC addresses? Because switches need to communicate with a router and switches only understand a MAC address.

Say a PC needs to send a packet to google.com. First the PC is gonna check it's arp table to see if google is on it's local network. When it discovers that it's not, the switch needs to connect to the router and that can only be done by using the MAC address of the router.

[tsbservice]

Re: Need some advice on learning networking

Just to go a little deeper on this subject....

Software resides on layer 7 of the OSI model. When I say software, I'm not talking about google.com, or YouTube or anything like that. Software is gonna fall into one or more of several categories: HTTP, HTTPS, POP. SMTP, ect. Depending on what category the "software" falls into is gonna determine what port needs to be opened. In conclusion, if the software has a bug, you can open the correct port but it's not gonna work. Make sense?

Absolutely. But in reality it isn't customer responsible to troubleshoot those kind of problems.

[BillyCarpenter]

Re: Need some advice on learning networking

Absolutely. But in reality it isn't customer responsible to troubleshoot those kind of problems.

That has been the reality in some cases. I've read about several times when this has been the case. The software guys would blame the network guys and the network guys would blame the software guys. Who's right? Who's wrong? That can be a devil to uncover.

For full clarity, we're talking about high level corporations that need special software in many cases.

[BillyCarpenter]

Re: Need some advice on learning networking

That has been the reality in some cases. I've read about several times when this has been the case. The software guys would blame the network guys and the network guys would blame the software guys. Who's right? Who's wrong? That can be a devil to uncover.

For full clarity, we're talking about high level corporations that need special software in many cases.

By the way, I left out some details. When we think "software", most likely we think about programs that most companies use, like Quickbooks, for example. But, remember, there's a big world out there where corporations pay software companies to write a program specifically for them. And sometimes that new program has a bug and the network guys may be the ones tasked with proving it's a software problem.


Enough of this, that's way beyond where I'm at right now. I just thought that it was interesting.

[slimslob]

Re: Need some advice on learning networking

By the way, I left out some details. When we think "software", most likely we think about programs that most companies use, like Quickbooks, for example. But, remember, there's a big world out there where corporations pay software companies to write a program specifically for them. And sometimes that new program has a bug and the network guys may be the ones tasked with proving it's a software problem.


Enough of this, that's way beyond where I'm at right now. I just thought that it was interesting.

And often there are industry specific software which can get quite specific. For years I worked on the copier, computer and phones for a bankruptcy attorney. They used a software that allowed them to quickly generate the needed forms for preparing a bankruptcy filing. Many car and RV dealers use a software that allows them to pull credit reports and print sales/leasing contracts. Accountants use software that that allows them to do a lot more than online tax filing websites.

[tsbservice]

Re: Need some advice on learning networking

That has been the reality in some cases. I've read about several times when this has been the case. The software guys would blame the network guys and the network guys would blame the software guys. Who's right? Who's wrong? That can be a devil to uncover.

For full clarity, we're talking about high level corporations that need special software in many cases.

I think they will blame each other no matter what. You're right on this special cases though.

[BillyCarpenter]

Re: Need some advice on learning networking

Things are getting interesting with the labs that I have to configure. We're slowly working our way up to building and configuring a college campus network.

Here's what we just completed: I took (1) Layer 3 switch and connected (3) Layer 2 switches to it. I connected (10) PC's to each Layer 2 switch for a total of 30 PC's. Moreover, I connected (1) web server to the Layer 3 switch.

That was just a warm up.

I then had to configure 4 vlans on each layer 2 switch - vlan10, vlan20, vlan30 and vlan100. I then had to configure the same 4 vlans on the layer 3 switch.

Still only getting warmed up.

I then had to configure 4 virtual gateways on the layer 3 switch for vlan10, 20, 30 and 100.


I then had to assign all the connected ports on the layer 2 switches to the correct vlans.

I then had to trunk the ports that ran from the layer 2 switch to the layer 3 switch. There were a total of 8 trunk ports that had to be configured.

After that....I ended up with inter-vlan routing between all the vlans, PC's and servers.

That was quite a job.

Here's the encouraging thing. I was able to do this on my own without having to watch the video in which the instructor shows us how to do it.

[BillyCarpenter]

Re: Need some advice on learning networking

Quick comment on Layer 3 switches.

At first I wasn't a big fan of layer 3 switches (they make layer 4 switches by the way). I've changed my mind on that. If you're gonna do inter-vlan routing, they are the only way to go, NO DOUBT. Huge time saver. Intervlan routing can be done with a standalone router but it requires more programming and the less of that you have to do, the better!!!!!!!!!!!!!


Edit: Apparently on larger networks, PC's aren't plugged directly in a layer 3 switch. The way I understand it is that layer 2 switches are run off the layer 3 switch and the PC's are connected to the layer 2 switch. Those layer 2 switches are commonly referred to as the "Access Switch"...for obvious reasons.

[rthonpm]

Re: Need some advice on learning networking

Quick comment on Layer 3 switches.

At first I wasn't a big fan of layer 3 switches (they make layer 4 switches by the way). I've changed my mind on that. If you're gonna do inter-vlan routing, they are the only way to go, NO DOUBT. Huge time saver. Intervlan routing can be done with a standalone router but it requires more programming and the less of that you have to do, the better!!!!!!!!!!!!!


Edit: Apparently on larger networks, PC's aren't plugged directly in a layer 3 switch. The way I understand it is that layer 2 switches are run off the layer 3 switch and the PC's are connected to the layer 2 switch. Those layer 2 switches are commonly referred to as the "Access Switch"...for obvious reasons.

Access switches have been most of what I see in enterprise environments, though generally there's only one or two VLAN's per geographical area, unless you're dealing with very special environments. Mainly I'll just see a single building or department VLAN, and maybe one for phones or some kind of special device.

Makes it much easier than trying to string a bunch of routers everywhere, doesn't it?


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[BillyCarpenter]

Re: Need some advice on learning networking

Access switches have been most of what I see in enterprise environments, though generally there's only one or two VLAN's per geographical area, unless you're dealing with very special environments. Mainly I'll just see a single building or department VLAN, and maybe one for phones or some kind of special device.




Sent from my BlackBerry using Tapatalk

That makes sense to me. From what I can tell, the only reason for using access switches is to increase the number of ports that PC's can connect to. That would confirm your statement that it's mainly used in an enterprise environment.

Makes it much easier than trying to string a bunch of routers everywhere, doesn't it?

Yes, sir. I hate every new technology that I'm introduced to because I know my brain is about to get a workout. Once I learn it, i love it.

On a serious note, you dang right it beats using a router.