Need some advice on learning networking

[BillyCarpenter]

Re: Need some advice on learning networking

Taking this CCNA course is a lot like being out in the ocean without a rudder. What I mean is that the amount of information is overwhelming and I don't know what's going to be on the test and what isn't that important. With that in mind, even though I'm only 50% done with the CCNA class, I decided to take a pretest to see how I'm doing. I didn't expect to pass because, like I said, I'm only half way done.


Well, the practice test was a humbling experience. I don't know anything about the CompTIA test but this CCNA is no joke. They want you know know the "theory" of all the protocols and some of it is mind blowing. So, the moral of the story is that I'm doubling back and studying the THEORY of well...anything that has to do with routing and switching.


PS - When you study something like this you realize that there are people in the world that are super smart that make us look like retards.

[BillyCarpenter]

Re: Need some advice on learning networking

I probably need to have my head examined for taking this CCNA class. The best way I can describe it is that its like climbing a mountain over and over again.

Mastering subnetting was climbing a mountain. The mountain that I'm climbing at the moment is the OSPF Routing Protocol. In order to pass the CCNA test, you must learn the theory of how it works. I went to bed last night feeling very frustrated. I woke up at 4 a.m. this morning and the first thing I thought about was OSPF. This is a very complicated process but I am making progress, finally!


Here's a brief overview:


When we run OSPF on 2 routers, the end goal is for the routers to share routes with each other until their routing tables look identical and then an algorithm is used to determine the Shortest Path.

Before any of that can be accomplished some things have to happen first.

I could explain it but it's very complicated and no one would understand what I'm talking about. If I ventured to guess, I would say I'll be on this for another 20-30 hours before I'm able to move on to the next mountain.

[BillyCarpenter]

Re: Need some advice on learning networking

I've heard a few people on here talk about a production network but I don't even know if they understand the true scope of a production network. The amount of expertise required to work on a production network is next level. The tiniest of mistakes could take down the entire network. Moreover, building a production network or troubleshooting it would require not only getting your CCNA but several years of experience.

As I sit here and go thru the theory of OSPF, I had one of those moments where the lightbulb comes on.


Question: What happens in OSPF if we take 5 routers with at least one interface in the same subnet and plug all those interfaces into a switch? Something amazing happens and it's genius. More on that later....


PS - I may have misspoke about taking years of experience to troubleshoot a prodution network but you better know your stuff.

[BillyCarpenter]

Re: Need some advice on learning networking

I think most of us that work on copiers were probably curious at a very early age at what made our toys work. I know that I was always asking my dad a lot of questions and driving him crazy. I remember it like it was yesterday. That's why I'm fascinated by routing and switching. It isn't enough for me to know how to configure it and get it to working. That can get boring. I need to understand the theory of how it works.


Some material in the CCNA class is a waste of time. I really don't need to know about the ISO (International Standards Organization). However, learning about theory is never a waste of time because it's instrumental when it comes to troubleshooting a problem.

While I will never fully understand the OSPF protocol, I have learned enough theory to glimpse into the genius of it.

I was so taken by the genius of the OSPF protocol that I began to wonder who was responsible for it?

A guy by the name of Edsger Dijkstra is the one who came up with it and he truly was a genius. He was the 1972 recipient of the ACM Turning Award, often viewed as the Nobel Prize for computing.


The complexity of OSPF has forced me to spend hours pulling out my hair and I'm not done yet. There are designated routers and backup designated routers that are elected. Then there are DROTHER routers. All of this design is to ensure the best possible route is taken and it generates the least amount of traffic (broadcast traffic) between the routers. And that's only scratching the surface.


If you want to know more about Edsger Kijkstra, I found this video:

[BillyCarpenter]

Re: Need some advice on learning networking

One of the first things that I had to learn was the different classes of networks and the IP ranges.


The multicast addresses are in the range 224.0.0.0 through 239.255.255.255.


Does anyone know why a network might need a multicast address?




Here's one reason: To cut down on broadcast traffic. For example, when we first install OSPF on 20 routers, all the routers will flood the network with "hello" packets that go out to every router. That can get messy and use up bandwidth. Instead, every router can be programmed to listen to a specific broadcast address (224.0.0.5 for OSPF) thus eliminating all the hello packets that are flooding the network.

[BillyCarpenter]

Re: Need some advice on learning networking

I learned something about myself while taking the CCNA class. I thought that I was working my ass off to learn this stuff and I was feeling "sorta" good about myself for making progress.


Here's what I learned about myself.


a.) I was not working hard. At least not hard enough. Instead, at times, I was sitting around feeling sorry for myself when I looked at the mountain of information that I needed to learn.

b.) I was not studying smart. You can study all day long but if you're not being smart about it, you're just wasting a lot of time.

Taking a 2-month break was a wise decision because it cleared my mind and allowed me to come back fresh. I was able to develop a strategy.

For the first time since starting this class, I feel like I've mastered most of the concepts that I've covered. But I also learned that I must keep reviewing old material and putting in time on the virtual labs every day because you will forget if you don't.

[BillyCarpenter]

Re: Need some advice on learning networking

I think routers and switches are so cool that everyone should learn 'em.


Let's talk about designated (DR)and backup designated (BDR) routers. Let's also talk about one more type of router - DROTHER router.


Before we talk about these 3 type of routers, I first need to paint a picture of the topology. Let's say that we have 10 routers with OSPF configured on all of them. When using OSPF the routers will share their individual routing tables with each other. That could get messy because Router 1 would send out it's routing table the other 9 routers and Router 2 would do the same and so on and so forth. That's a lot of traffic going out over the network.


This is where the designated router comes in. Each router has an ID #. For example 9.9.9.9 would be the ID # for R1. The other routers would have an ID# lower than 9.9.9.9. (We program in the ID #'s ourselves)

Are you with me so far? Good.

When OSPF is first enabled it will look at all of the ID #'s and elect a designated router. The highest ID # wins. The next highest # is elected as the backup designated router.


Still with me? Good.

Once we have elected a Designated Router, it alone will send out the routing tables to the other 9 routers thus eliminating the need for the other 9 routers to advertise their routing table to the other routers.

And about the backup designated router? That's in case the designated router goes down. Kinda like the President and vice president relationship.


This completes today's lesson.


PS - Any router other than the DR and BDR is labeled as a DROTHER Router because they remain in a different state and don't send out in data except to the DR and BDR.

[BillyCarpenter]

Re: Need some advice on learning networking

I'm starting to get in to some of the more advanced routing features and it struck me that mathematics is used in many different ways. That's true whether we're designing a network or configuring a router. It's very important to understand the role that mathematics play in networking.

Since we're dealing with computing, of course we're dealing with a base 2 number system. But you have to be able to convert binary to decimal and vice-versa.


By using mathematics alone we're able to cut down on the amount of broadcast traffic on a network. I assume that this is the way it was done before VLANS.

But mathematics go much deeper than that in networking. It also plays a key role in setting up a routing protocol or an access list. Really, there's not much that doesn't involve mathematics when it comes to networking and it can get very complex.

[BillyCarpenter]

Re: Need some advice on learning networking

About that math that I was talking about? Here's a blurb out of my CCNA book that talks about Route Summarization (Supernetting) and why it is critical.

Route summarization, or supernetting, is needed to reduce the number of routes that a router advertises to its neighbor. Remember that for every route you advertise, the size of your update grows. It has been said that if there were no route summarization, the Internet backbone would have collapsed from the sheer size of its own routing tables back in 1997!


Routing updates, whether done with a distance-vector protocol or a link-state protocol, grow with the number of routes you need to advertise. In simple terms, a router that needs to advertise ten routes needs ten specific lines in its update packet. The more routes you have to advertise, the bigger the packet. The bigger the packet, the more bandwidth the update takes, reducing the bandwidth available to transfer data. But with route summarization, you can advertise many routes with only one line in an update packet. This reduces the size of the update, allowing you more bandwidth for data transfer.


Also, when a new data flow enters a router, the router must do a lookup in its routing table to determine which interface the traffic must be sent out. The larger the routing tables, the longer this takes, leading to more used router CPU cycles to perform the lookup. Therefore, a second reason for route summarization is that you want to minimize the amount of time and router CPU cycles that are used to route traffic.

[BillyCarpenter]

Re: Need some advice on learning networking

I continue to review material that I previously covered in the first half of the CCNA course. Some of this stuff seemed extremely difficult to wrap my mind around the first go round but now it seems simple.


One theme throughout routing and switching that you'll run into over and over again is broadcast traffic or protocols that flood the network with different kinds of packets. Routers block broadcast traffic and so do VLANS. It's something that you need to know inside & out.

Earlier I set up 3 different labs for inter-vlans. The first time I used a regular router with 1 interface in each VLAN. The 2nd lab was a router on a stick. The 3rd lab I used a layer 3 switch. A layer 3 switch in the easies and it's also the preferred method.


I'm looking forward to moving on to something new. I think the next chapter is Network Security. I think.

[BillyCarpenter]

Re: Need some advice on learning networking

Let's talk about VLANs. Most of us know about a VLAN. They allow us to segment larger groups of PC's into smaller groups thus reducing broadcast traffic and they provide an extra layer of security.


But what if we have VLAN 10 that has 5 users on floor 2 and 9 users on floor 10. In other words the VLAN information must travel from Switch 1 to Switch 2. Is that gonna work? Nope. At least not out the box. Some configuring must be done.


A little background first. The PCs don't know that they are part of a VLAN. The switch knows but the PCs have no idea.

A little more information is necessary to understand how this is gonna work.

A switch has 2 kinds of ports: a.) access port and b.)trunk port. Keep that in your memory bank for a minute.


Here's the way VLAN's work. Data frames are spliced open and a VLAN tag is inserted at (Layer 2) Switch 1. It is then transported over the trunk interface to switch 2 where the VLAN tag is stripped away and the packet is forwarded to the correct device.

You need to be aware of the 802.1q protocol. This is turned off by default and must be turned on for all trunk ports.


That's it.

[BillyCarpenter]

Re: Need some advice on learning networking

I just read something that I didn't know and hadn't thought of. On a switch VLAN 1 is the default VLAN and it's a security risk.


The Vlan1 itself is not insecure, even many still occupy it. The insecure thing is that everyone knows that it is the Vlan by default. And as already mentioned, you can be a victim of attacks by this vulnerability. Therefore it is recommended not to use it to switching/routing end devices.

It is also recommended to leave disabled ports (shutdown) that are not occupying.

[BillyCarpenter]

Re: Need some advice on learning networking

I just read something that I didn't know and hadn't thought of. On a switch VLAN 1 is the default VLAN and it's a security risk.


The Vlan1 itself is not insecure, even many still occupy it. The insecure thing is that everyone knows that it is the Vlan by default. And as already mentioned, you can be a victim of attacks by this vulnerability. Therefore it is recommended not to use it to switching/routing end devices.

It is also recommended to leave disabled ports (shutdown) that are not occupying.

Hhhmmmm....this is wrong.

As it turns out, there is a default and a native VLAN. They are 2 totally different things. Both the default and native VLAN are VLAN 1 from the factory.

It should be noted that the default VLAN 1 cannot be changed or deleted.

The native VLAN, however, can and should be changed.

You may be asking yourself what is the purpose of a native VLAN and why do we need it. Here's the quick answer.....



.....A switch that uses vlans will necessarily add a VLAN tag to the data packet and forward it only to that VLAN. However, we may have a case where we have some devices that don't belong to a VLAN thus only the native VLAN supports untagged (NO VLAN) traffic. We simply need to change the native VLAN from VLAN 1 to some other number to avoid a hop attack at layer 2.


I probably did a poor job of explaining it.

Here's a better explanation:

[BillyCarpenter]

Re: Need some advice on learning networking

I managed to get in a few hours of study today. I'm still reviewing old material.

One last tip: Any unused port on a switch should be taken out of default VLAN 1 and assigned to some garbage VLAN and put in the shutdown mode.

[BillyCarpenter]

Re: Need some advice on learning networking

I am officially done with reviewing material. It was quite beneficial. I'm exactly at the 50% mark in terms of overall progress. It's amazing to me that I've put in this much time and effort and I'm only half way done.

Because CCNA is vendor specific, they can drill down to specifics unlike some other vendor neutral certificates.

Earlier today I previewed my next chapter which is: Hot Standby Router Protocol. What is this, you ask?

In a small to medium network, you have a single Internet Service Router and 1 edge router. But in a production network, you're gonna have 2 ISP routers and multiple edge routers. In other words, the network will be designed to have no single point of failure. The name of the game is: redundancy redundancy redundancy.


The game plan is to watch a few videos and get an idea of how it works and then to do a deep dive into the protocol. It's looks complicated.



EDIT: I've only been watching the first video for about 10 minutes and it's very interesting.

Pro Tip: Best practice is to have 2 Internet Service Provider Routers and make sure they are from 2 different providers. For example, one internet provider should be ATT and the other should be Verizon, for example.