subnetting

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ok been trying to get my head round this one, i understand that with addressing - i can say have the following :
192.168.101.45
255.255.255.240

i've got 4 bits of last octet as my hosts.
Now i've been using a caluclator which admitedly is a bit of cheating - but i'm trying to get to grips with doing it in my head, if i've got 4 bits left for host id - i'm looking at 2^4-2 for the number of networks available - i'm wondering how u go about breaking this down into ip ranges to apply to your differant networks, i may be missing somthing totally ovbious and i may have got some of my statements wrong here as well, just trying to get me head round it.....

 

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Hi there,

Here youll have 14 hosts and 14 subnets.....

your network id will be 192.168.101.32 for ip address 192.168.101.45

and subnets will be 192.168.101.0......32-48-64-80-96-112-128-----and so on, with the block size of 16.

to find the block size 256-240 = 16

each of these subnets will have 14 hosts...ie 192.168.101.32-33-34-35-36-----45-46...47= broadcast add


the easiest way is to determine the network id first of the given ip address... find out which network it belongs to then the task should be easy..

hope this helps

 

i feel like a donkey with a carrot in front of it - i can almost tuoch it i think..and then its away again...thanks though that does make it a bit cleaer - just gonna keep going over this till it settles in the old noggin

 

my head feels like its caving in...

 

Two things:

First, this link must be posted all over our site by now but it's just about the best place in the world (or at least on the net) to learn subnetting without frying your brain:

http://www.learntosubnet.com/

Second, the Network+ exam *does not* require that you know how to subnet, so unless you are learning for your own personal development, you can save a few brain cells and not stress out over learning subnetting for this exam.

 

i'm also just wondering why i cant have a subnet mask of 255.255.255.128 = or is this allowed? leaving me 7 bits for the hosts?

 

Looking at the network part of the address, a 128 mask only allows two alternatives, either the first bit is 0 or it is 1. In the past, these were not available as network addresses (called subnet zero and the 'all 1's ' networks). Most modern software and hardware will permit their use, but this is usually specified specifically. For example with cisco IOS it requires the command 'subnet zero' (which is on by default).

For exams, it varies: with N+ you will never be asked; for CCNA it is usually specified what is allowed; for CCNP it will usually be assumed that subnet zero is enabled; for Microsoft exams, it used to be disallowed - someone more knowledgeable than me will have to post to say if this is still the case or not.

 

Actually, it's ip subnet-zero, and it's enabled by default in IOS 12.0 and above.

Cisco's VERY good about either making it clear as to which situation you'll use, or by providing well-formed choices where only one choice could possibly be correct.

Haven't seen Network+ for a while, so I can't judge whether CompTIA does or not... with their "SME" program as it is, I'd not be too optimistic.

 

Try searching the forum for 'Kobem'.

You'll find loads of useful advice there that hasn't been used yet.

 

Hardy har, har har.

 

http://www.learntosubnet.com/

This is how I learnt; although I have completely forgotten how to do it now as I never use it

 

Hey Dude,

Thanks for the link. I am also learning or trying to learn subnetting and I find it an absolute nightmare since the book I am using to prepare for the exam has the wrong information. Because of that I ended up getting more confused. Any other links that you might know of?