It is said that practically all-zeros and all-ones subnets are not used.
Let us consider an a network $220.127.116.11/25$
Here Network ID is represented by using $25$ bits and Host ID using $32-25=7$ bits.
Binary Representation : $11001000.11001000.00001101.00000000$
Last 7 bits which represent HID are $0000000$
Suppose we want to divide the network into $4$ subnets, so we will borrow $2$ bits from Host.
So the subnets will be
$11001000.11001000.00001101.00000000$ - $18.104.22.168/27$
$11001000.11001000.00001101.01000000$ - $22.214.171.124/27$
$11001000.11001000.00001101.10000000$ - $126.96.36.199/27$
$11001000.11001000.00001101.11000000$ - $188.8.131.52/27$
Now it is said that all-zeros and all-ones subnets are not used, then let us consider -
(i) the IP addresses ranging from $184.108.40.206 - 220.127.116.11$ which should belong to all-zeros subnet and
(ii) the IP addresses ranging from $18.104.22.168 - 22.214.171.124$ which should belong to all-ones subnet
Will belong to which subnet/network or will remain unallocated ?