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 —- ————-
001 210.20.30.33 to 210.20.30.62
010 210.20.30.65 to 210.20.30.94
011 210.20.30.97 to 210.20.30.126
100 210.20.30.129 to 210.20.30.158
101 210.20.30.161 to 210.20.30.190
110 210.20.30.193 to 210.20.30.222
These do not include the network and broadcast addresses.
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