Exam AZ-104 topic 5 question 139 discussion

A /25 CIDR notation means that 25 bits are used for the network portion of the address, and the remaining 7 bits are available for the host portion. An IPv4 address has 32 bits in total. With /25, the first 25 bits define the network. The remaining 7 bits are used to define individual hosts within that network. With 7 bits for the host, you can have 2^7 = 128 total addresses. However, 5 addresses are reserved (network address, broadcast address, and 3 by Azure), leaving you with 123 usable addresses for VMs and other resources.

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.

vote C