Actually just like regular math, Subnetting also has a calculator. If you go out to
then their download page. All the way at the bottom is the subnet calculator. Download that and you can configure your subnet the way you'd like.
Subnetting is basically playing around with the subnet mask. for example.
My Dallas office quickly ran out of IP Addresses using a regular Class B address of 172.16.4.0/255.255.255.0. I was able to increase the network of 254 addresses to 510 by adjusting the subnet mask to 255.255.254.0. (I was able to do this because I was in the private address range) What this essentially does is place one bit back to the host by taking it away from the network address. This one bit gave me a range of
172.16.4.1 to 172.16.5.254
Now to reverse that.....
I have a full class B address of 172.16.4.0 and I need at least two different subnets. by borrowing one bit from the host address I could split my class c into two different subnets using a subnet mask of 255.255.255.128. This would give me the range of
172.16.4.1 to 172.16.4.126 = Network 1
172.16.4.128 to 172.16.4.254 = Network 2
This is a down and dirty way of explaining it using a subnet calculator. The real good thing about this particular subnet calculator is that it shows you which bit is the network address and which bit is the host address.
NOW if you want to know the manual way, let me know. I also know that but I don't use it that much. It's kind of like knowing how to do multiplication without a calculator first. If you know how to do it then understanding how it works is that much easier.
You are correct about it does not matter which address you choose if you don't plan to connect to the internet, but....keep in mind that things change. I would stick with the private address range and not venture outside of that. Even if there is a 1 in a million chance that your network will connect to the internet, it has been my experience that 1 chance will always come back to haunt you. Always look forward when designing networks, it will help you or whoever takes over for you in the future.
Also good to take note of Jimbo's advise on numbering. Make ranges for all your equipment. This is my current configuration for my Dallas office...
Routers/switches = 172.16.4.1 - 20
Production Servers = 172.16.4.21 - 40
Management Servers = 172.16.4.41 - 60
Test Range = 172.16.4.61 - 80
Manual DHCP = 172.16.4.81 - 100
Auto DHCP = 172.16.4.101 - 5.139
Not Assigned = 172.16.5.140 - 5.254
Note that I don't use the entire range of addresses, not assigned range is for growth. This plan also works well for my smaller offices. Every piece of equipment has their range on the network, that way I can keep track of them much better and plan for any future expansion.
david e
*end users are just like computers, some you can work with...others just need a simple reBOOTing to fix their problems.*