Subnetting

ally_uk

Ok guys I am in the process of learning how to subnet

So regarding subnetting I know the default classes of a subnet mask

Class A = 255.0.0.0 = Network. Host. Host. Host
Class B = 255.255.0.0 = Network. Network. Host. Host
Class C = 255.255.255.0 = Network. Network. Network. Host

And the logical AND process in which I obtain a network address from a ip address and subnet Mask

I am still having a few basic problems in understanding some concepts.


Can somebody give me a Clear explanation as to why we subnet I know it's to segment networks and to create more broadcast domains

Also what are the downfalls of the default subnet mask classes I know you can only create a certain amount of networks using them . But I am still having difficulty understanding

Also the Ip address which you use for your network where the hell does it come from? your ISP???

Thanks

Sie

Im no expert but i'll try and explain a bit.

Can somebody give me a Clear explanation as to why we subnet I know it's to segment networks and to create more broadcast domains

Subnetting is used to split up large networks into smaller subnets

The main benefits are:

Reduced network traffic

Optimized network performance

Simplified management

Helps to facilitate spanning of large geographical distances

Also what are the downfalls of the default subnet mask classes I know you can only create a certain amount of networks using them . But I am still having difficulty understanding

The subnet mask you use is dependant on the amount of networks and hosts you need for each subnet.

Also the Ip address which you use for your network where the hell does it come from? your ISP???

The IP address ranges people use within home business networks are made up from the private IP address range and are used as they are none routable.

These are made up from:

Class A
10.0.0.0 through 10.255.255.255

Class B
172.16.0.0 through 172.31.255.255

Class C
192.168.0.0 through 192.168.255.255

The ISP would provide the external IP address, and 9 time out of 10 the internal address is translated to the external using NAT.

As the result of another topic I have started looking through the CCNA book by Lammle and he explains subnetting very well. I would take a look if you get chance.

Or www.learntosubnet.com is also good.

telecomops101

Can somebody give me a Clear explanation as to why we subnet I know it's to segment networks and to create more broadcast domains ???

Subnetting is used to create sub-networks from a registered IP class or private IP address. Let's say you were given a registered class B address of 150.150.0.0. Your subnet mas would be 255.255.0.0. Without subnetting you would have 65,534 networks (2 to the power of 16 network bits -2), with 65,534 hosts (2 to the power of 16 hosts bits -2) on each network. Say you only needed each subnet to handle 200 hosts. From this you could see that having 65,534 avaible hosts is a waste, so with subnetting you can steal 8 of the host bits to create a maximum of 254 available hosts (2 to the power of 8 hosts bits -2) on each network. Your new subnet mask is now 255.255.255.0. You can see this meets your requirments and you still have room to grow regarding hosts.

Also what are the downfalls of the default subnet mask classes I know you can only create a certain amount of networks using them . But I am still having difficulty understanding

I believe my above example should shed light on this question. Your IP address and subnet mask go together. The subnet mask lets you differentiate between the network and host portion of the IP address. Also the Ip address which you use for your network where the hell does it come from? your ISP???



I hope this helps you.

jrmcent

Your subnet mas would be 255.255.0.0. Without subnetting you would have 65,534 networks (2 to the power of 16 network bits -2), with 65,534 hosts (2 to the power of 16 hosts bits -2) on each network.

Looking at this made me think. If you have a 255.255.0.0, which is the default for Class B, you wouldn't have any subnets at all. In order to have a subnet you have to borrow bits from the hosts, which would be third and fourth octet. So I think you would only have 1 network, with 65,534 hosts. Not positive, but I am pretty sure.

Darthn3ss

i believe you are correct, your valid hosts should be 150.150.0.1 - 150.150.254.254... with the default mask.

royal

Just an FYI, but when working with networks, it's 2^n. It's only 2^n-2 when working with host bits. Read here for more information.

telecomops101

Looking at this made me think. If you have a 255.255.0.0, which is the default for Class B, you wouldn't have any subnets at all. In order to have a subnet you have to borrow bits from the hosts, which would be third and fourth octet. So I think you would only have 1 network, with 65,534 hosts. Not positive, but I am pretty sure.



Yes, I was incorrect. You are right there is only one network without subnetting. I appologize for any confusion. After I looked at it again I cant' beleive I made that logical mistake.

EdTheLad

The reason behind subnetting is to conserve address space.Instead of a service provider allocating an full class C address to a company, it can split the class C address space into multiple networks and assign these networks to different companies.
Without subnetting:
Company A asks the ISP for a public address space as it has 4 hosts
that need to connect to the internet.Company B also wants an address space for 10 of its hosts to connect.
ISP gives addresses 193.10.10.0/24 to company A and 193.10.11.0/24 to Comp B, A uses 4 addresses and B uses 10, each class C address supports 254 hosts.494 addresses have been wasted.
With subnetting :
Company A gets address 193.10.10.0/29 and B gets 193.10.10.16/28.
As you can see with subnetting alot of addresses get saved.

ally_uk

How is this relevant in a actual job?


To me it just seems like useless theory how would this provide you with any benefit?

Who cares if you waste that amount of IP addresses?

Something just seems strange about the whole process like it's more hardship than it's worth.

this guy seems to know what he is talking about

http://techrepublic.com.com/5208-6230-0.html?forumID=3&threadID=196947&messageID=2053670

royal

For most businesses, they won't care. It's more for the really large enterprises that want to segment their links into many different broadcast domains. That and ICANN needs to subnet and supernet the address spaces they hand out to preserve as many IPs as possible. You should still know how to subnet though. As a Windows and/or Cisco Admin/Engineer, you need to know why a subnet mask is even there, what it does, what subnet to put into Active Directory Sites and Services, etc...

EdTheLad

In the link you provided the guy is using private addressing, he will also need to use NAT to access the internet. Subnetting was developed before NAT.If you plan to keep a network private it doesnt really matter about subnetting too much but subnetting gives you the ability to provide better summarization techniques, which means smaller routing tables, faster lookups and as a result faster data forwarding.
As for service providers they need to subnet as the public address space is finite so it provides a mechanism for them to spread the addresses allocated to more customers which means more money.
At the end of the day everyone is using subnetting in one way or another, its extremely easy to do once you understand the idea.

ally_uk

So what your basically saying is that Subnetting is pretty useless

The majority of places Use NAT

Is subnetting even worth knowing? my collegue always laughs at me when I'm saying i'm about to undertake my CCNA he says subnetting especially is useless knowledge and is mainly used by geeks who over think things.

EdTheLad

I'm not saying its useless!!, the fact is if you cant subnet you wont be able to understand complex wildcard masking, summarization , prefix-list etc. It is a basic skill needed. With private networks and NAT you can create a network without subnetting,but if you want to be a proper engineer you must understand how to subnet at a minimum.Most private networks i know use subnetting even if they only break a major network in two.
Don't worry about your fellow colleagues, they can try leading you astray in order for themselves to look better.If you want to continue Cisco studies and even pass the ccna you will need to know subnetting inside out.Once you get it you will wonder what all the fuss is about.

sprkymrk

ally_uk wrote:

So what your basically saying is that Subnetting is pretty useless

No. Subnetting is one of the very foundations of of networking and TCP/IP.

ally_uk wrote:

The majority of places Use NAT

Many places use NAT. Many don't. When IPv6 becomes standard there will hardly be a need for NAT anymore.

ally_uk wrote:

Is subnetting even worth knowing? my collegue always laughs at me when I'm saying i'm about to undertake my CCNA he says subnetting especially is useless knowledge and is mainly used by geeks who over think things.

He is clueless. Don't listen to him, and don't ever take his advice on picking lottery tickets. He won't be in the business long, or else you'll leave him in the dust as you advance far beyond his seemingly miniscule understanding of networking.