If the 0 subnet number cannot be used, the netmask will have to change to FFFFFFE0, or 255.255.255.224, to give 3 subnet bits. The subnet numbers in binary are then: 000 001 010 011 100 101 110 111. The numbers 000 and 111 are illegal, leaving 6 networks. The valid IP addresses would then be:

Net#    Address Range —- ————-

These do not include the network and broadcast addresses.