Identify Purpose of Subnetting?

Hello,

The Comptia updated Net+ Objectives ask for you to Identify Purpose of Subnetting.
What does this mean? All I know is what subnet goes with what IP. Is this enough or do I need to be able to do subnetting in my head?

Thx in advance.

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vex

Identify Purpose of Subnetting = Know when and why you would need to subnet.

Thats how it registers in my head.

You dont really have to be able to do it in your head. The test center usually gives you something to write on, so you should be able to do it on paper.

Cheers

geekgodes

So when and why would I subnet? To make more hosts on my network?

I think I've got the major part the binary to decimal piece.
I MISSED SOMETHING! I DON"T UNDERSTAND THE LAST STEP!

I've taken this from subnetonline.com:
Subnetting, or splitting the hosts part, is possible by defining a subnet mask. To start your way in determining the subnet mask that is most suitable for you, determine the number of required subnets. Possible number of subnets are none, 2, 6, 14, 30, 62, 126 or 254. Convert the number of required subnets to binary. For example:

30 subnets = 00011110 GOT THIS PART!

Now, count from right to left the numbers until you reach the last bit set to one. In this case that is five bits. GOT THIS PART!

WHAT"S GOING ON HERE???
***To form a subnet from this number, apply the number of bits on the subnet mask (?), from left to right. So, that would look like this:

WHERE DID THEY GET THIS?
5 bits from left to right = 11111000 binary = 248 in decimal.

??? PLZ HELP!

Judd

Ok, here's an easy way to subnet.

I'm assuming you understand the classes of subnets...A-B-C

Let's say you have IP 192.168.10.1 with a default subnet mask of 255.255.255.0. This is 1 network with 256 hosts. All the 255's in the subnet represent network bits, the 0 represents the host bits. This means that you can technically have 256 hosts...2 .3 .4.-.254 .255 .256

This isn't always practical if you wish to have more than one network so you can subdivide that IP address and get more networks with fewer hosts per network.

So let's say you want 5 networks from that one IP address of 192.168.10.1. The formula is 2^x -2 to figure this out. So, 2^3 = 8 - 2 = 6. You can have 6 useable networks by subnetting this address. So you are really "borrowing" 3 network bits from the 3rd octet. So by using these 3 bits to make more networks you have to turn them into 1's because they are network bits now. So, 128+64+32=224. Now 224 is your new subnet mask in the 4th octet. 5 bits remain, so 2^5 – 2 leaves you with 30 addressable hosts on each new network.

IP = 192.168.10.1
Subnet = 255.255.255.224

How do you know what your 6 new networks are? Easy, subtract 224 from 256 to get your first network address. 256-224=32 Then add 32 to each new number until you reach the subnet mask of 224. So, 32+32=64+32=96+32=128+32=160+32=192+32=224 the subnet mask.

So here are you new networks:
192.168.10. -
32-63
64-95
96-127
128-159
160-191
192-223

Of course, these numbers represent network and broadcast addresses, useable addresses are in between these.

A little over simplified but hope this helps!

Webmaster

@geekgodes: I don't mind the questions at all, but this is the second time you asked something to which you can find the answer in my Network+ TechNotes, so I suggest reading those first. In this case:

www.techexams.net/technotes/networkplus/tcpipsuite.shtml

I wrote:

Calculating the correct subnet masks for specific scenarios is not something you will be tested on for the Network+ exam but it is important to understand what subnetting is.

What it is is explained in that link above.

Regardless, subnetting is an important subject when it comes to networking. To get a better and more detailed understanding of what it is and how it is done, try www.learntosubnet.com

jlewis92683

here is an explination of subnetting and its purpose. subnetting is used to divide up your network mostly for the sole purpose of broadcast domains and controlling network traffic. standard subnetting does not give you more hosts, you actually loose hosts at a rate of two per subnet one for network and one for broadcast. You shouldn't have to worry much about breaking down subnets unless you are going for cisco certs. hope this helps

geekgodes

To Webmaster,

I actually did read the TechNotes, and many other explanations. None of them seemed to answer the 2.7 CompTia Objective of purpose of subnetting.
Also, there seemed to be an assumption on how you achieve the X portion of 2^x-2.

Besides, haven't you heard the saying, "The only stupid question is the one that isn't asked."? Also, I thought that is what forums were for... questions.

All I wanted was a simple and brief explanation, which seemed to be hard for me to find anywhere.

Thanks for everyone's help.

Webmaster

Really, don't start this negative defensive crap on me today... I clearly stated: "I don't mind the questions at all"

The purpose of subnetting is explicitely mentioned in those TechNotes:

This process is known as subnetting. The main reason to divide a Class A, B, or C network into smaller subnets is to use the available address space more efficiently. For example, your company is assigned a Class B network, which allows for 65534 different host addresses. It would be a waste of addresses to use the entire range for a single network with 200 nodes. Instead, the class B address can be subnetted by using Class C subnet mask, or a classless subnet mask.

geekgodes

So harsh!
I am not being negative or defensive. I also don't need to have my message be deemed crap.

I also read, your comment about not minding questions, so why bring up that I asked a similar question twice at all?

Simply, I did not understand a part of the TechNotes and other resources, and I only wanted clarification on what I was reading and how to apply it to the CompTia Objectives.

Besides, aren't we all hear to help each other?

eurotrash

a bed has two sides...

geekgodes

THX!

Webmaster

I also read, your comment about not minding questions, so why bring up that I asked a similar question twice at all?

Maybe because I'm trying to help.

As I clearly stated, I don't mind an additional questions in the forums, that's what they are for. However, that doesn't mean I won't be doing my job and point you to posts or TechNotes that already cover the answers to your questions, to make sure you haven't missed those for any reason, to make sure you understand the topic, and hence help you pass.

Besides, aren't we all hear to help each other?

What do you think I'm doing here and have been doing for 3 years every day...? And while you're at it, why do you think I created these forums in the first place.

Besides, haven't you heard the saying, "The only stupid question is the one that isn't asked."? Also, I thought that is what forums were for... questions.

That's defensive and negative while I was not attacking, just trying to help.

geekgodes

To be honest...
that's all I ever wanted help and some additional clarification.

Thanks for your patience and help.

Webmaster

And that's exactly what you can expect, and includes suggestions to read certain sections of my TechNotes, other sources, previous topics, and advice to use the search option to see if a question has been posted before etc.etc. Which all in no way means I 'mind' the post/question itself. You would have received a PM with the subject 'removed post' if that were the case. And I should have picked a better word than 'crap', I guess it looks a lot more harsh when you read it than when I typed it. Don't hesitate to ask any other questions.

porengo

Johan, has anyone ever told you that you don't "crap" where you "forum?"

Webmaster

jsobrinog

Maybe the topic for this replay can answer the question.

Subnetting is an important part of a good network logical topology.
What do this means? , there are some net admins that use a complet 192.168.0 subnet for their networks, but through time, they figure that their nodes are reducing and they experience heavy traffic. Here is where subnetting comes, oferring a discret ip designation and creating diferente "lans" "segments" "subnetS" that interact only in their own borders.

:S hope this can explain.

P.D didnt read the answers for this post , i just reply it jejejeje sorry.

davidh

I didnt get this either when i first started learning about subnetting. You have to look at it from a bigger perspective, most of us are used to configuring small, single site lans with class c networks and/or not understanding how routers work.

**You will need to have an understanding of how subnetting works and how to do it. Understanding the binary conversion of an ip addresses is crucial to comprehending this**

The purpose of subnetting is to minimize wasting network addresses when splitting networks.

scenario:
You have been assigned a Class C range of IP addresses

You have 180 servers. These computers generate heavy traffic and you've decided to seperate the computers into 6 seperate network segments.

A router on a remote network receives a packet, and sees that it is destined for ip 192.168.0.66 and starts sending it across the network.

Once it reaches the router that controls network 192.168.0.x (the main incomming router for your entire class c network), the router looks at its routing table...

Network ID IP addresses within this network

192.168.0.32 ip's x.x.x.33 - x.x.x.62
192.168.0.64 ip's x.x.x.65 - x.x.x.94
192.168.0.96 ip's x.x.x.97 - x.x.x.126
192.168.0.128 ip's x.x.x.129 - x.x.x.158
192.168.0.160 ip's x.x.x.161 - x.x.x.190
192.168.0.192 ip's x.x.x.193 - x.x.x.222

because ip address 192.168.0.66 in binary is
11000000 10101000 00000000 01000001
and the router for 192.168.0.x knows that this ip address is on a network with a subnet of 255.255.255.224 (configured on the router)
11111111 11111111 11111111 11100000

it compares the ip and the subnet mask
11000000 10101000 00000000 01000001
11111111 11111111 11111111 11100000
the router can see that the network id ends after the first 3 bits in the ip address (see below)
11000000 10101000 00000000 010 00001
........................................................../\
and according to the first 3 bits in the last octet of the ip address, (010) which is 64 in binary, the router knows to send the packet to the router that controls network 192.168.0.64 (look at the above routing table)

questions?

igor_yuri

Hi~ you were asking where did X from "2^x-2" came from? It's actually a Base 2 binary. Lets say a Class C 192.168.67.200

N.N.N = Network ID - 192.168.67
H = Host = .200 = 8 bits

Now, remember each octet represents 8 bits. Since, its a Base 2 getting the number of bits from host part which is 8. Therefore, 2^8 - 2 = 254 Host ; now you might wanna know where did we get the -2 part. It's a default value for 1 and 0. Zero(0) for Network ID and One(1) for Broadcast ID.

Cass B 130.70.66.195

N.N = Netowrkd ID - 130.70
H.H - Host ID - 66.195 = 16 bits

Simple as 2^16 - 2 = 65,534 Host

Now, solve for Class A. You should have 16,777,214 Host

I hope this helps. Wish me luck tomorrow for my Network+ exam!

micro420

I haven't read through this whole post with replies, but to answer your question in respect to the Network+ exam, which I just took today and had this very same question, the answer was something to the effect of "consolidation of small networks from one big network."

The other responses, which were not correct were:
increase bandwidth
decrease congestion (maybe...)
????? this option was something ridiculous and off the wall

Hope this helps

TechJunky

Try this link...

Should help explain a little better.

http://www.akgaming.com/study/subnetting.html

I made this when I was having a hard time with subnetting.

elathrop

That was invigorating!

Here is the way I would answer the question “What is the purpose of subnetting?”

To break up your network into smaller segments and to be better able to organize collision domains.

IE, You could keep your subnets on separate switch ports and more easily manage or recognize them by their IP addresses. It certainly is only a matter of organizing things. A switch alone would seperate collision domains but you may want an easy way of knowing which one is which. You could seperate by departments or classes, etc.

I’m sure nothing like that will be on the test, but I had fun taking a crack at it.

Ciao and Bow Wow