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minimum number of bits

the minimum number of bits that can be borrowed to form a subnet
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Rick HobbsRETIREDCommented:
Depends on the network address class.
As rickhobbs notes, it depends on the address class.  Classful subnetting is used so infrequently I'll skip that possibility and assume you are using classless addressing.

Let's assume you have a CIDR-style address range assigned to you that you wish to subnet.

You cannot use the "last" or "all-ones" subnet as that is reserved for network broadcasts.

You typically should not use the "first" or "all-zeroes" subnet by tradition, but some devices do allow use of this subnet.  For Cisco devices, for example, you enable "ip subnet-zero".

So for practical purposes, the "minimum number of bits" is two, giving you four subnets. You can't use the last, so you get two workable subnets (or three if all devices on subnet zero allow for subnet zero addressing).
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