There are 32 bits available, under IP4, If you want to use 25 bits to define the network address,
32 - 25 means 7 bits are left for hosts and other stuff and 7 bits can represent 127 hosts, (64 +
32+16+8+4+2+1= 127.) but since you can't use the top and the bottom ones as they are used for other purposes, that leaves 125 free IP address numbers for hosts. There is usually a Gateway address in there somewhere as well as the network address so (125-2 =123) 123VM can be connect to /25 subnet.