Rebecca,

The answer to your question is simple if you try and break the problem.

1) you need 16 subnets

2) your subnetmask is 255.255.255.0 so I'm guessing your dealing with a Class C network

Now, if we want to answer the above question, by following the rules correctly, then this is the formula that to defines how many bits are required to give us the amount of subnets we need (16):

2^x-2. That is, 2 to the power of X, minus 2.

IF your wondering why the -2, well in theory, we shouldn't use the first or last subnet, but in practice we always do

Check the subnetting pages for more info on that.

So, after a few calculations, we find that:

2^4=16-2=14 subnets.... not good enough

2^5=32-2=30 subnets. This is the closest we can get to 16 or more subnets.

So, we need to reserve 5 subnet bits in order to produce the 30 subnets. Our new subnet mask will be as follows:

255.255.255.248

We need to translate it into binary in order to show the 5 bits we have reserved for the subnets:

255.255.255.1111 1000

__________

___

Network~~~Subnet~host

Each subnet range, assuming 192.168.0.0 network:

---Network ID----Broadcast ID

1: 192.168.0.0 - 192.168.0.7, valid host range: .1 to .6

2: 192.168.0.8 - 192.168.0.15, valid host range: .9 to .14

3: 192.168.0.16 - 192.168.0.23, valid host range: .17 to .22

4: 192.168.0. 24 - 192.168.0.31, valid host range: .25 to .30

...

...

32: 192.168.0.248 - 192.168.0.255, valid host range: .249 to .254

You must remember that the 1st and last subnets, that is 192.168.0.0 and 192.168.0.248 should not be used.

As noted, this answer is considered correct for a totally theoretical question, e.g if you got this question in your ccna exam, they would expect you to answer it as I showed you.

If on the other hand you just wanted to split your office or home network, then you could use the 2^4=16 subnets and apply them to your network since it would also work.

Both answers will work in practice, but when you look at it from a pure theoretical point, only the 1st answer is considered correct, regardless if the 2nd one would work aswell in a real environment.

I hope I haven't confused you

Cheers,