This question already has an answer here:
Lets say I own 126.96.36.199/24. If I subnet to create 188.8.131.52/25 and 184.108.40.206/25, have I effectively given up all those /24 addresses?
What happens to the /24 designation in terms of routing? What would be the result of pinging one such address previously assigned to a host (ex: 220.127.116.11/24)?
From a theoretical standpoint, a number like 18.104.22.168/24 and 22.214.171.124/25 are distinguishable--the first network has an address 24 bits long and the second, 25 bits. Therefore, it appears that a router should be able to distinguish between these two subnets and I should be able to use my old /24 addresses alongside my new /25 addresses. In the /24 subnet, I would have 256 addresses at my disposal, while in the two /25 subnets, I would have 128 addresses each.
I realize this is silly, but I don't know why. (One implication would be a single number 126.96.36.199 being used in many subnets /24, /25, /26, /27, ...)
So what is wrong with the above reasoning? How does the subnetting designation work?