Learning beginners networking in a college course, have some questions!

[Oldgamer]

So I am in some college courses and learning the very basics of computer technical support and have a class which is basically to prepare us for the CCNA certs. My math is rusty as hell, and at my age my memory gets a bit foggy, but it seems that we must learn to convert decimals to binary, binary to hexadecimals, and back. I have gotten the basic conversion down for simply converting the 8 bits of binary to decimal and vice versa. I have been told that we cannot use a calculator for any of this. In addition I was told that Cisco's exams also will not allow you to use a calculator. So I assume they want to see that you at least know the concepts of conversions. But to my real question, in a regular job for networking, and even computer tech support or both, how much of this do you calculate on your own manually? Or do companies expect that you will be using calculators for conversions if needed, for speed? I would like to know what to expect should I get through this and pass the CCNA exams. I hear from my instructor it is pretty rough, and that as a newbie, you really need to study and know your stuff.

Anyway, would like some input. Thanks folks!

 

[Mushkins]

The CCNA (when I got mine years ago) is no joke of a test. No calculators allowed, and all of the virtual command line stuff has no help menu, it *strictly* accepts the commands needed to complete that question. I believe I was allowed a pencil and a single piece of scrap paper. If you can, take the test that's actually two separate tests, each covering half the curriculum. I don't know if they offer the all-in-one test since they added all the VoIP crap to it, but I spent an entire summer straight self-studying nearly full time for the test and if I didn't brush up on that last chapter about WAN tech five minutes before walking out the door I wouldn't have passed. A single college level class is not enough prep to pass it, but it's a good foundation.

There might have been two or three questions on converting binary to decimal or hex to decimal. Is it something useful to be able to do in your head? Yeah, especially with IPv6 slowly coming and having those obnoxious Hex IP addresses. Will your employer ever genuinely care if you do it in your head vs using some sort of calculator? Highly unlikely, they care more about you doing it right than doing it in your head, though you might get an interview question or two asking you to do it as part of a skill assessment.

Learn it for the test, but don't stress it. Knowing how to configure a static route or set firewall rules is about 100000x more important in both real world and the test than converting decimal to hex in your head.

 

[Oldgamer]

The CCNA (when I got mine years ago) is no joke of a test. No calculators allowed, and all of the virtual command line stuff has no help menu, it *strictly* accepts the commands needed to complete that question. I believe I was allowed a pencil and a single piece of scrap paper. If you can, take the test that's actually two separate tests, each covering half the curriculum. I don't know if they offer the all-in-one test since they added all the VoIP crap to it, but I spent an entire summer straight self-studying nearly full time for the test and if I didn't brush up on that last chapter about WAN tech five minutes before walking out the door I wouldn't have passed. A single college level class is not enough prep to pass it, but it's a good foundation.

There might have been two or three questions on converting binary to decimal or hex to decimal. Is it something useful to be able to do in your head? Yeah, especially with IPv6 slowly coming and having those obnoxious Hex IP addresses. Will your employer ever genuinely care if you do it in your head vs using some sort of calculator? Highly unlikely, they care more about you doing it right than doing it in your head, though you might get an interview question or two asking you to do it as part of a skill assessment.

Learn it for the test, but don't stress it. Knowing how to configure a static route or set firewall rules is about 100000x more important in both real world and the test than converting decimal to hex in your head.

OK, thanks for the input. Yea, apparently this is to prep us for the first part of the CCNA. The instructor said just about what you did, that we will get a pencil and peice of paper, and not much else..lol

They gave us a pretest to see what we know right now, to gauge what needs to be covered and who needs catching up. I got only 51 % roughly, because I still no very little about routing, and networking. We have been given access to the netcad site, and they had us download a Cisco Packet Tracer program. The program is for practicing and making sure we have connections done right I am assuming, just by looking at it. Looks like you just click and drag the icons of your routers, modems, switches, etc. then pick the types of cable that should be appropriately applied.

Well I may ask further questions as I go along in this course. Thanks again!

 

[ScottMac]

IMO, you need to know it because it's the root of everything you will be doing in networking. It is how you will address, divide networks into subnetworks, filter stuff in, filter stuff out, filter who gets to do what and where.

It's just not that hard, 0's & 1's. x^0, x^1,x^3 ...

For the test, they'll give you a handful of subnets, and you have to determine if they belong to the target address they provide. Trust me; most of the answers are composed of the most frequent student errors and nearly all will look correct to a brief glance.

Learn binary, octal, hex (and decimal, of course) and you will be able to subnet in your head (or maybe on your hands ... you can count to 31 on one hand!). Calculators are never needed. People that need them don't know what they are doing, or why.

Depending on your role in whatever organization you end up in, you may need to do binary/octal/hex calculations a lot (many times daily) or you may only need it occasionally ... but on those occasions, Murphey says there will be no calculator available. Amaze your friends and co-workers!! Do grade-school math in your head like a champ!!

For the test, remember: if you understand the "why" and how to do the tasks, there's nothing they can throw at you that you can[t figure out. Studying to just pass a test leaves you wide open for embarrassment on your "technical interview," where you are likely to be asked "what's wrong with this," or "what do we have to change to make this scenario function?" The answer is not "C" ... you have to do some head scratching and explain your answer.

The folks here are usually helpful if there's a concept you don't understand, feel free to come back and ask. However, most won't do your homework for you; be prepared with specific questions.

Good luck!

 

[lif_andi]

In my experience, which is not alot but some, you rarely have to convert binary to anything in networking, but you must know how to subnet and to do it pretty fast and understand what the binary represents. So imo, they want you to understand what it is you are doing, and how you can do it, because it gives you something to build on for what you will be doing.

EDIT: The Packet Tracer program is extremely helpful. Do not underestimate its power. With it you will learn all basic routing and switching, how to set up routing protocols, spanning tree and so much more. It is very good.

 

[drebo]

Subnetting is extremely important, and it does require a good grasp of binary math. Knowing where subnet boundaries are (for instance, you can't have a subnet of 10.0.0.12/29) and being able to easily identify masks (both wildcard and subnet masks) is very important.

After a while, the easy ones will jump out at you...like knowing that a /29 is a 255.255.255.248 mask, etc, and recognizing the patterns will get easier.

But, yes, it is extremely important to know and I do use it every single day.

 

[alkemyst]

Trust the CiscoPress Library. Get the Network Simulator they offer.

Don't brain dump, you will pass the test but you will be totally clueless forever.

I just posted this in another thread:

http://1examamonth.com/ is excellent

http://hackingcisco.blogspot.com/ is excellent

http://www.cisco.com/web/learning/certifications/index.html is excellent

For CCNA there are tons of great freebies.

 

[alkemyst]

IMHO skip binary math if you don't know it and learn the patterns.

http://www.aelius.com/njh/subnet_sheet.html

Learn what a /24 is and learn to count up or down if you need too.

 

[lif_andi]

Totally forgot about the genius tool to learn binary to decimal: The Cisco Binary Game

 

[alkemyst]

cisco has good tools to learn esp at lower levels.

 

[Oldgamer]

Hey those are great links alkemyst, thanks! I am reading one of my text books now, and digesting all of this stuff. What I have gotten so far is /24 is the class C subnet mask? /8 is an A, and /16 is a B? the /24 indicates the numbers of 1's in the binary code for the actual subnet mask number? So I guess getting the classes down asap is important. Anyway, I will probably come back later is I get stumped on some concepts and ask questions. I am certainly not looking for anyone to do my homework..LOL

Really appreciate the links though!

 

[drebo]

Nope, classes are not at all important. Ignore the fact that they exist, because they're not used.

What's important is understanding CIDR notation. This is also referred to as "slash" notation. /24 means that the first 24 bits (this would be known as the "network" portion of the mask, and the remaining bits are the "host" portion) of the subnet mask are 1s. So, your subnet mask is 11111111.11111111.11111111.0. If you convert that to decimal, that's 255.255.255.0. That means that there are 2^24 possible "networks" with 2^8 possible hosts.

There used to be a rule where you weren't supposed to use the first or last network, and there still is a rule where you can't use the first or last host (network address and broadcast address, respectively) so you really get a -2 on the number of hosts.

Similarly, if you were to look at a /8, you'd have a subnet mask of 11111111.0.0.0 or 255.0.0.0. That's 2^8 networks and (2^24)-2 hosts per network.

The beauty of this is that you're not constrained by "classful" networking. We can have a /9 or a /29 or a /19, and the rules for calculation are the same.

 

[drebo]

Also, with respect to "subnetting," you can break larger networks into smaller subnets.

That /8 above, for instance, could be broken down into multiple smaller networks. If, for instance, we wanted /24s from that /8, we could find out how many /24s we'd get by taking the number of bits in the larger network and subtracting it from the number of bits in the smaller networks. 24 - 8 = 16, so a /8 can have 2^16 total /24s. That's the basic premise behind subnetting.

Ultimately, everything is a subnet of 0.0.0.0/0.

 

[Mushkins]

Also, with respect to "subnetting," you can break larger networks into smaller subnets.

That /8 above, for instance, could be broken down into multiple smaller networks. If, for instance, we wanted /24s from that /8, we could find out how many /24s we'd get by taking the number of bits in the larger network and subtracting it from the number of bits in the smaller networks. 24 - 8 = 16, so a /8 can have 2^16 total /24s. That's the basic premise behind subnetting.

Ultimately, everything is a subnet of 0.0.0.0/0.

Subnetting is definitely a topic i've seen a lot of people struggle with. Ultimately the best advice to learn it is to just get a whole bunch of practice problems and soldier through them. It eventually just seems to "click" for people and then they go from super frustrated to "oh, that's really easy, I get it."

 

[drebo]

Oh, one other thing...don't ever use the term "supernet." It makes you look like a fool or a hipster...not sure which is worse.

 

[alkemyst]

Hey those are great links alkemyst, thanks! I am reading one of my text books now, and digesting all of this stuff. What I have gotten so far is /24 is the class C subnet mask? /8 is an A, and /16 is a B? the /24 indicates the numbers of 1's in the binary code for the actual subnet mask number? So I guess getting the classes down asap is important. Anyway, I will probably come back later is I get stumped on some concepts and ask questions. I am certainly not looking for anyone to do my homework..LOL

Really appreciate the links though!

As others said, everything is really though about in a class-less way now.

The important things is to remember the private address spaces and learn cidr notation.

 

[alkemyst]

Oh, one other thing...don't ever use the term "supernet." It makes you look like a fool or a hipster...not sure which is worse.

supernetting is still talked about. You could call it summarization as well.

 

[alkemyst]

Also, with respect to "subnetting," you can break larger networks into smaller subnets.

That /8 above, for instance, could be broken down into multiple smaller networks. If, for instance, we wanted /24s from that /8, we could find out how many /24s we'd get by taking the number of bits in the larger network and subtracting it from the number of bits in the smaller networks. 24 - 8 = 16, so a /8 can have 2^16 total /24s. That's the basic premise behind subnetting.

Ultimately, everything is a subnet of 0.0.0.0/0.

A typical 'exam question' is exactly something along these lines. Usually you are given a address pool to break out into 6 or more networks. Usually the math only works one way to complete the problem.

 

[Oldgamer]

Hey quick question! I am studying like a mad man right now. Finally wrapped my head around a pretty quick easy way to convert Hex numbers to binary, then to decimals. I looked up a youtube vid from the Networking Doctors, and it gave a pretty quick method for doing the conversion. Anyway, I am wondering how big of a Hex number they might throw at you on the CCNA test? I figure if the number is really large I will have to memorize my chart; 2048 - 1024 - 512 - 256 - 128- 64 - 32 - 16 - 8 - 4 - 2 - 1 as an example.

Are they just small numbers for conversion to see that you have the method down? Or do they throw large complex numbers for conversion?

Anyway, I haven't gotten to the CIDR notations yet, some of it looks like memorization is needed on it.

 

[alkemyst]

Hey quick question! I am studying like a mad man right now. Finally wrapped my head around a pretty quick easy way to convert Hex numbers to binary, then to decimals. I looked up a youtube vid from the Networking Doctors, and it gave a pretty quick method for doing the conversion. Anyway, I am wondering how big of a Hex number they might throw at you on the CCNA test? I figure if the number is really large I will have to memorize my chart; 2048 - 1024 - 512 - 256 - 128- 64 - 32 - 16 - 8 - 4 - 2 - 1 as an example.

Are they just small numbers for conversion to see that you have the method down? Or do they throw large complex numbers for conversion?

Anyway, I haven't gotten to the CIDR notations yet, some of it looks like memorization is needed on it.

Hex is really just used in computing which MAC address gets priority.

So as large as a MAC address and it's usually just the last 3-4 digits.

CIDR is binary. However; in reality I recommend learning the patterns. Start at /24 and 256 (254 usable) and then double going down in number and halve going up. You always lose 2 for the network and broadcast.

It's rare to see anything deeper than a /19-20. /24's are common, /30's for your point to points as well. Some /26,27,28's.