which subnet would I use?

[mattburles]

Which subnet would I use to supernet the networks 192.168.100.0 and 192.168.101.0?


Is it 255.255.255.224, 255.255.248.0, 255.255.254.0, or 255.255.0.0?

Thanks for the help!

 

[mikesgroovin]

Before I start, I just would to note for the record, I'm a lousy teacher...


Well, lets try to make your brain work a little... subnetting and supernetting are tough for anyone unless you can get it explained to you the right way. So, I'll try a simple way:
Think of supernetting networks as the opposite of subnetting networks. Why do you subnet networks? To divide the larger network into smaller ones right?
Supernetting is the opposite, instead of "borrowing" bits to increase your number of sub-networks within a larger network, you are "borrowing" bits from the other side of your sub-networks.

Sooooo, you have a "Subnetwork" mask of 255.255.255.0 and you need to increse or "super" your mask in order to allow more of your sub-networks to talk to each other.

255.255.255.0 is
11111111.11111111.11111111.00000000 in binary where all of the 1s are your network bits and the zeros are your node bits. You need to go left and borrow network bits and
turn them into node bits until your AND statements for "subnet masking 101" works out.

11000000.10101000.01100100.00000000 = 192.168.100.0
11111111.11111111.11111111.00000000 = 255.255.255.0
---------------------------------------
11000000.10101000.01100100.00000000

11000000.10101000.01100101.00000000 = 192.168.101.0
11111111.11111111.11111111.00000000 = 255.255.255.0
---------------------------------------
11000000.10101000.01100101.00000000

Using the 255.255.255.0 is this case would not allow the 100.x and 101.x networks to talk to each other.

However.....

11000000.10101000.01100100.00000000 = 192.168.100.0
11111111.11111111.11111110.00000000
---------------------------------------
11000000.10101000.01100100.00000000

11000000.10101000.01100101.00000000 = 192.168.101.0
11111111.11111111.11111110.00000000
---------------------------------------
11000000.10101000.01100100.00000000

Using the second subnet mask allows them to talk to each other.
There are 3 answers that would work, but 2 of them would be like grinding coffee beans in a blender when you had a coffee grinder.
There is one answer that when put into a subnet mask, the range for that particular network would be from 192.168.100.0 to 192.168.101.255 which is exactly what you want.

So, I hope that makes sense...

 

[mattburles]

Thanks that helped out a lot!

I have one other question..

Can someone explain to me Why hosts in 192.168.12.0 cannot communicate with hosts in 192.168.10.0?

 

[S0ULphIRE]

How big do you need this subnet to be? e.g. do you also have hosts in 192.168.13.0 which need to communicate with the .12 and .10 networks?
And to quickly answer your question, it'd most likely be your subnet is wrong.
Just post up...
1. the networks you want to network
2. the ip addressing scheme you've got in place

 

[mikesgroovin]

Well, I think that the OP is just referring to defaults here. In which case the subnets are 255.255.255.0. The networks the the OP has in place are the ones in the post 10.0 and 12.0.

Short answer to the question is just as S0ULphIRE mentioned... your subnets are incorrect. Refer to the above post of mine to perform AND statements to get them to communicate.

Current Setup:
11000000.10101000.00001010.00000000 = 192.168.10.0
11111111.11111111.11111111.00000000 = 255.255.255.0
---------------------------------------
[B]11000000.10101000.00001010.00000000[/B]

11000000.10101000.00001100.00000000 = 192.168.12.0
11111111.11111111.11111111.00000000 = 255.255.255.0
---------------------------------------
[B]11000000.10101000.00001100.00000000[/B]

Since subnetting further (making more zeros into ones from left to right) wont work, we need to go left. Above, look at the 2 AND statements I made. The results were:
11000000.10101000.00001010.00000000 for the 10.0 network
and
11000000.10101000.00001100.00000000 for the 12.0 network

We aren't changing your IP scheme, that stays. So we need to change your subnetmask right?

Your starting subnet mask is:
11111111.11111111.11111111.00000000 (255.255.255.0)

Supernetting will allow us to make the ones to zeros, moving from the right to the left. So, let's start with the next bit! We'll make your subnet mask:
11111111.11111111.11111110.00000000 (255.255.254.0)
ok, now to see if this mask makes your IP networks match up:

11000000.10101000.00001010.00000000 = 192.168.10.0
11111111.11111111.11111110.00000000 = 255.255.254.0
---------------------------------------
[COLOR="red"][B]11000000.10101000.00001010.00000000[/B][/COLOR]

11000000.10101000.00001100.00000000 = 192.168.12.0
11111111.11111111.11111110.00000000 = 255.255.254.0
---------------------------------------
[COLOR="red"][B]11000000.10101000.00001100.00000000[/B][/COLOR]

Now, wait??!?!? That didn't change a thing. The first time around, we knew that since, in the third octet, your results were:
x.x.00001010.x
and
x.x.00001100.x
The first, 0, doesn't need to be changed since they are already a match. (right most 0... always go from right to left in binary)

Ok, if you are in agreement that the first "supernetting" was pointless then you are well on your way to perform the next test. Let's make the node bit from a 1 to a 0 and then give it another try! We'll remove the next bit and make your subnet mask:
11111111.11111111.11111100.00000000 (255.255.252.0)

Let's give this subnetmask AND statement try!

11000000.10101000.00001010.00000000 = 192.168.10.0
11111111.11111111.11111100.00000000 = 255.255.252.0
---------------------------------------
[COLOR="red"][B]11000000.10101000.00001000.00000000[/B][/COLOR]

11000000.10101000.00001100.00000000 = 192.168.12.0
11111111.11111111.11111100.00000000 = 255.255.252.0
---------------------------------------
[COLOR="Red"][B]11000000.10101000.00001100.00000000[/B][/COLOR]

ok, we are getting closer, but we still got this as the third octets:
x.x.00001000.x
and
x.x.00001100.x

Getting rid of that next 1 will do the trick. (third bit from the right in the second result)

Let's make the node bit from a 1 to a 0 and then give it another try. We'll remove the next bit and make your subnet mask:
11111111.11111111.11111000.00000000 (255.255.248.0)

ok, one last time... let's give this AND statement a try!

11000000.10101000.00001010.00000000 = 192.168.10.0
11111111.11111111.11111000.00000000 = 255.255.248.0
---------------------------------------
[COLOR="SeaGreen"][B]11000000.10101000.00001000.00000000[/B][/COLOR]

11000000.10101000.00001100.00000000 = 192.168.12.0
11111111.11111111.11111000.00000000 = 255.255.248.0
---------------------------------------
[COLOR="SeaGreen"][B]11000000.10101000.00001000.00000000[/B][/COLOR]

Hey, we have a match now!
So, in order for those two network to "speak" without a static route (lol)
You need to give ALL of those nodes a 255.255.248.0 subnet mask. This would cover from 192.168.8.0 to 192.168.15.255
Here's why: One network node from 192.168.8.0 down would be 192.168.7.255. Let's do the AND to see if they would talk!

11000000.10101000.00000100.11111111 = 192.168.7.255
11111111.11111111.11111000.00000000 = 255.255.248.0
---------------------------------------
[COLOR="red"][B]11000000.10101000.00000000.00000000[/B][/COLOR]

11000000.10101000.00001000.00000000 = 192.168.8.0
11111111.11111111.11111000.00000000 = 255.255.248.0
---------------------------------------
[COLOR="red"][B]11000000.10101000.00001000.00000000[/B][/COLOR]

Results in the third octet were:
x.x.00000000.x
and
x.x.00001000.x
Nope, you would need to move one more over which would get rid of the 1 in the 00001000 making it a change from
11111111.11111111.11111000.00000000 (255.255.248.0)
to
11111111.11111111.11110000.00000000 (255.255.240.0)

Doing an AND statement with those subnets would make them match and encompass 192.168.0.0 all the way to 192.168.15.255


Just remember that in your AND statements:
0 AND 0 = 0
1 AND 0 = 0
1 AND 1 = 1
(going down from IP address to subnet mask of course)


I hope that helped you understand a bit better. It sounds like a couple of canned questions from a study guide or test of some sort though...
the original post had a multiple choice answer and if you look at your quote on the 2nd question...

Thanks that helped out a lot!

I have one other question..

Can someone explain to me Why hosts in 192.168.12.0 cannot communicate with hosts in 192.168.10.0?

The "W" in "Why hosts in 192.168.12.0" is capitalized... like you copied and pasted it or something.