You are quite welcome. I often find that an actual real world example is a whole lot more useful than all of the theory you would need to create it but without a good example.
I don’t really bother thinking about them as A/B/C anymore because we have CIDR notation so you are not limited to those classes. Make sure you use the private address ranges for sure (unless you have public IP’s to play with) .
If you stick to subnet masks of only 255 or 0’s then it’s fairly straight forward.
You have the network part of the address (where the 255’s are) and the host part (where the 0’s are)
As long as all the devices you want on the same “network” all have the same network part and a unique host part then you are golden.
given an IP address a.b.c.d
255.255.255.0 makes a.b.c your network address and .d your host address’
255.255.0.0 makes a.b your netwok address and c.d your host address’
255.0.0.0 makes, you guessed it, a your network address and .b.c.d your host address’
(you can also have 255.255.255.255 and 0.0.0.0 but don’t think about that it’ll make your brain hurt)
255.255.255.0 can also be written as /24
255.255.0.0 is /16
255.0.0.0 is /8
Count the number of bits being used (hint, 0-255 is an 8 bit number), remember that each part of an IP address is called an Octet and remember that the subnet mask tells you which bits of the IP represent the subnet.
Then the class bit tells you which address you can use internally.
10.0.0.0/8 - 10.x.y.z are available
192.168.0.0/16 - 192.168.x.y are available
so you can say 10.7.1.0/16 (255.255.0.0) then anything that starts with 10.7 (the first 16 bits) are on the same network.
172.16. is a tiny bit more complicated because it uses part of the second octet but not all of it. That’s when you have to start looking at “proper” subnetting to take full advantage but you can use 172.16.0.0 /16 through 172.31.0.0/16 or, for example 172.21.5.0/24
I hope that kinda makes sense, I’m a techie not an educator!!!