ip adress and subnetting

[blackeagle]

sup guys i really need help to understand how this works got an exam on it  soon and i don't manage to understand it !!
ps:i don't need the solution i have it i need to understand how to do it thx in advance for ur help

your business owns IP network ( 123.64.0.0 )with the net  mask ( 255.254.0.0 ) , the Administrator Network Company

 desire to decompose the network into 8 sub networks containing respectively :

15000 machines.

2000 machines.

I 024 machines.

500 machines .

200 machines .

10000 machines.

30 machines.

17000 machines.

2.1 Provide for each sub network ( 16 points )
2.1.1 The network address.

2.1.2 The net mask.

2.1.3 The broadcast address (broadcast) .

[P!X3LTR0N]

I think you want this?
http://www.wikihow.com/Calculate-Network-and-Broadcast-Address

[blackeagle]

i did find this before posting here but couldn't understand it so if some1 could explain that exercise step-by-step that would be great

[RedBullAddicted]

Ok, I am not a mathgician. But I already did some subnetting in my life and thats how I do it:

Check if the task is possible:
255.254.0.0 = 11111111.11111110.00000000.00000000 = 2^17 (count of 0's) = 131072 addresses available
15000 + 2000 + 1024 + 500 + 200 + 10000 + 30 + 17000 = 45754
131072 > 45754 (means its possible)

First Subnet

1 .How many bits do you need for 15000 hosts:
11111111 111111 = 2^14 = 16384 (means we need 14 bits in our subnetmask for the host part -> the host parts are 0's in the netmask)
11111111 11111111 11000000 00000000 = 255.255.192.0

2 . Calculate first and last address:
first = (addr && netmask)
last = (addr && netmask) + !netmask

First:
123.64.0.0 = 01111011 01000000 00000000 00000000
255.255.192.0 = 11111111 11111111 11000000 00000000

     01111011 01000000 00000000 00000000
&& 11111111 11111111 11000000 00000000
     01111011 01000000 00000000 00000000 = 123.64.0.0

Last:
    01111011 01000000 00000000 00000000
 + 00000000 00000000 00111111 11111111
    01111011 01000000 00111111 11111111 = 123.64.63.255

The Answer for the first subnet:
2.1.1 = 123.64.0.0
2.1.2 = 255.255.192.0
2.1.3 = 123.64.63.255
CIDR = /18
Host = 123.64.0.1 - 123.64.63.254

Second subnet:

starting point: 123.64.64.0

1. How many bits do you need for 2000 Hosts:
11111111 111 = 2^11 = 2048
11111111 11111111 11111000 00000000 = 255.255.248.0

First:
123.64.64.0 = 01111011 01000000 01000000 00000000
255.255.248.0 = 11111111 11111111 11111000 00000000

     01111011 01000000 01000000 00000000
&& 11111111 11111111 11111000 00000000
     01111011 01000000 01000000 00000000 = 123.64.64.0

Last:
   01111011 01000000 01000000 00000000
+ 00000000 00000000 00000111 11111111
   01111011 01000000 01000111 11111111 = 123.64.71.255

The answer for the second subnet:
2.1.1 = 123.64.64.0
2.1.2 = 255.255.248.0
2.1.3 = 123.64.71.255
CIDR = /21
Host = 123.64.64.1 - 123.64.71.254

Now go on and build the next subnets

Hope that helps!

[Mordred]

RBA was way faster to post a solution, but I vouch for the correctness of his method.

To be of at least a bit of help, I recommend also checking out subnetting using the magic box method and subnetting using the square method.

Both of these give exactly the same results as if you computed it by hand, but they rely more on intuition and computing with decimal numbers rather than on computing with binary numbers.

[blackeagle]

does it make a difference if i make one subnet before another ? for example if i start with 17000 machines then do the subnet fr the 15000 machines will the network address broadcast address and netmask of the 15000 machine subnet change ?

[RedBullAddicted]

the netmask will stay the same. The network and broadcast address will change. Do you have an idea why this is the case? Try to build the subnet for the 17000 machines. Will 14 bits for the hosts still be enough or would you need more?

[blackeagle]

i did try to start with a subnet for 17000 machines and now i could understand everything just to make sure this i'll show you my result

17000 machines
ip 123.64.0.0
netmask 255.255.128.0
brodcast 123.64.127.255

15000 machines
now the starting ip would be 123.64.128.0
the subnetmask is 255.255.192.0
broadcast is 123.64.255.255

[RedBullAddicted]

Great Thats correct. If you really did that with pen and paper and not with a subnet calculator, I think subnetting shouldn't be a problem for you anymore.

[blackeagle]

yep i've done it with pen and paper and that's all because of you
thank you RedBull you just taught me something new

[turtleseal1]

Sorry to hop in on this thread and ask more questions, but after seeing this post, I thought now was the perfect time to learn sub-netting. Right now, I understand all of the work on the first subnet, or at least I think i do, but I do not understand how 123.64.64.0 is the starting point for the second subnet, any explanations or resources would be greatly appreciated!

[RedBullAddicted]

Hi turtleseal1,

not a bad question It does not necessarily have to be 123.64.64.0. I just took it casue it was the next free address.
Your complete range goes from 123.64.0.0 to 123.65.255.255. I already used the range from 123.64.0.0 - 123.64.63.255.
So the next possible address I could start from is 123.64.64.0. But you can start with something else. You just can't use the address space you already used.

Hope that helps

[turtleseal1]

Thanks for the answer. I built the second subnet before checking what you had to see if I had the right idea, and I was really confused about where you got that from, but oh cool, I think everything makes sense now! Thanks again