Now to put our knowledge to use… You are working for TechMen and your boss told you that you need to create a subnet to create 3 networks with one given address. The address he gave you was… 192.168.46.0. First thing you notice is that the first octet starts with 198 and this puts you in a Class C address. That only gives you a subnet mask of 255.255.255.0 to work with. That means you cannot touch the first 3 octets (198.130.10) because they are given to you. Now to work with this, you only have 8 bits to work with all in the last octet. Remember how I said you c198.130.10an steal host bits to make network bits? This is what we have to do here…

Now here we need to find out on how to make 3 networks out of the last octet of all 0s. To find out what bits we need to define the network we must use the following equation:

2^{# of bits} – 2 = # of networks

So we need 3 networks so we try to plug in 2 bits.

2² – 2 = 2 networks

So lets try 3 bits….

2³ – 2 = 4 networks

You may wonder why you subtract 2, but that will be covered when we assign the address space. Even though we overshot with 4 networks and only needed 3, which is okay. It is better then having 30 possible networks and only needing 3. By doing the closest amount and reaching our goal, we are conserving address space, which in the long run helps when you are in the need of expansion.

So by using 3 bits, that only leaves us with 5 host bits to play with.

This now makes our network address 192.168.46.1110000 which is equivalent to… 192.168.46.224, and our subnet mask is 255.255.255.224. Remember we took 3 bits from the host bits in the last octet.

Wow now we have 5 host bits, how do we use them and what do they mean? Well they are there to be assigned to nodes on the network like mentioned before. With these bits, we can find out how many hosts we can have connected to each network. We do this by the same equation as finding the networks.

2^{# of bits} – 2 = # of hosts

In this case, we have 5 host bits so…

2⁵ – 2 = 30

You may wonder why you subtract 2, but that will be covered when we assign the address space. This means we can have 30 nodes connected to each subnet that we created.

Now we must put all of this to work, everything we know comes down in the assigning of address spaces. Here I will explain why we subtract 2 from both the network and host bit equations, show you how to properly conserve address space for your network, and how to properly assign addresses.

First we will talk about the Subnets that we have created. We came up with 11100000 to be our subnet mask and network address. We cannot stop there though; we now have to put the subnet's to work by finding out what we can use. With 11100000, we can only use the 111 to define the network and leave the 00000 to be used to define the hosts. So what numbers can we use? With the equation it did say we were going to have 6 networks, so here they are. We subtract 2 within the equation because of the 2 illegal networks that are possibilities.

In blue is the given IP and subnet, and below shows each network and subnet that we got from stealing 3 of the 8 bits in the last octet. We can easily choose the first 3 networks which is normally the best to keep organized on what networks are used on a certain subnet.