Private IP Address ranges and Subnet masks - please explain

[switch_abx]

There are three Classes of IP Ranges:
Class A: 0.0.0.0 - 127.255.255.255 with subnet mask 255.0.0.0
Class B: 128.0.0.0 - 191.255.255.255 with subnet mask 255.255.0.0
Class C: 192.0.0.0 - 123.255.255.255 with subnet mask 255.255.255.0

Within Class A the private IP range is:
10.0.0.0 - 10.255.255.255 with subnet mask 255.0.0.0

Within Class B the private IP range is:
172.16.0.0 - 172.16.255.255 with subnet mask 255.255.0.0

Within Class C the private IP range is:
192.168.0.0 - 192.168.255.255 with subnet mask 25.255.255.0

Question: Can I combine a LAN Private IP range of Class A e.g. 10.15.0.0 (10 10.15.0.1 - 10.15.0.255) with a Class C subnet mask 255.255.255.0?

Could this cause problems? What are the pros and cons? If this is unusual, please explain. Am I supposed to follow the rules set by the Internet "authorities" i.e. the body who oversees the internet? Am I free to do so?

I haven't found any plausible explanation as to why all those IP ranges have their own associated subnet masks.

[CrowdAds]

[switch_abx]

sorry I made some typos:

Originally Posted by switch_abx

Class C: 192.0.0.0 - 123.255.255.255 with subnet mask 255.255.255.0
should read:
Class C: 192.0.0.0 - 223.255.255.255 with subnet mask 255.255.255.0

192.168.0.0 - 192.168.255.255 with subnet mask 25.255.255.0
should read:
192.168.0.0 - 192.168.255.255 with subnet mask 255.255.255.0

[SKI]

That is a completely legitimate addressing scheme, Switch. You are simply creating a subnet within the 10.0.0.0/255.0.0.0 range. No issues at all doing this. Advantage: allows you to grow your network in the future by several methods. Only disadvantage I can think of is that if you want to grow into a larger SINGLE subnet, you'd need to change subnet masks for all addresses of the original subnet.

[switch_abx]

SKI, thanks for your feedback!

Originally Posted by SKI

That is a completely legitimate addressing scheme, Switch. You are simply creating a subnet within the 10.0.0.0/255.0.0.0 range. No issues at all doing this. Advantage: allows you to grow your network in the future by several methods. Only disadvantage I can think of is that if you want to grow into a larger SINGLE subnet, you'd need to change subnet masks for all addresses of the original subnet.