How do I determine how many bits I need to borrow from the host to create my subnet structure? How do I get my subnet mask?

You need subnets to seperate the groups of computers because you want them on different broadcast domains, or they are physically separate, or you need to do some kind of filtering between the subnets.

So you basically have to figure out how many computers you will have in each subnet and then you break up your address space in a way that makes sense.

Lets assume for a second that on 3 of subnets you will have between 0-62 computers and the other two 2 will have between 0-30 computers you might subnet things like this.

- 195.3.2.0/24 -> break into 4 subnets of 62 hosts - 1 - 195.3.2.0/26 (195.3.2.1-195.3.2.63, 62 usable addresses) - 2 - 195.3.2.64/26 (195.3.2.65-195.3.2.127, 62 usable addresses) - 3 - 195.3.2.128/26 (195.3.2.129-195.3.2.191, 62 usable addresses) - 195.3.2.192/26 -> break into 2 subnets of 30 hosts - 4 - 195.3.2.192/27 (195.3.2.193-195.3.2.223, 30 usable addresses) - 5 - 195.3.2.192/27 (195.3.2.225-195.3.2.255, 30 usable addresses) 

But on the other hand if one of your networks need to have about 120 hosts, 2 of them need about 60 hosts, and 2 need about 32 hosts you would have to break up your networks differently.

How do I determine how many bits I need to borrow from the host to create my subnet structure? How do I get my subnet mask?

You need subnets to seperate the groups of computers because you want them on different broadcast domains, or they are physically separate, or you need to do some kind of filtering between the subnets.

So you basically have to figure out how many computers you will have in each subnet and then you break up your address space in a way that makes sense.

Lets assume for a second that on 3 of subnets you will have between 0-62 computers and the other two 2 will have between 0-30 computers you might subnet things like this.

- 195.3.2.0/24 -> break into 4 subnets of 62 hosts - net 1 - 195.3.2.0/26 (195.3.2.1-195.3.2.63, 62 usable addresses) - net 2 - 195.3.2.64/26 (195.3.2.65-195.3.2.127, 62 usable addresses) - net 3 - 195.3.2.128/26 (195.3.2.129-195.3.2.191, 62 usable addresses) - 195.3.2.192/26 -> break into 2 subnets of 30 hosts - net 4 - 195.3.2.192/27 (195.3.2.193-195.3.2.223, 30 usable addresses) - net 5 - 195.3.2.224/27 (195.3.2.225-195.3.2.255, 30 usable addresses) 

If one of your networks need to have about 120 hosts, and the other 4 need about 30 hosts you would have to break up your networks differently.

- 195.3.2.0/24 -> break into 2 subnets of 126 hosts - net 1 - 195.3.2.0/25 (195.3.2.1-195.3.2.127, 126 usable addresses) - 195.3.2.128/25 -> break into 4 subnets of 30 hosts - net 2 - 195.3.2.128/27 (195.3.2.128-195.3.2.159, 30 usable addresses) - net 3 - 195.3.2.160/27 (195.3.2.161-195.3.2.191, 30 usable addresses) - net 4 - 195.3.2.192/27 (195.3.2.193-195.3.2.223, 30 usable addresses) - net 5 - 195.3.2.224/27 (195.3.2.225-195.3.2.255, 30 usable addresses)