All possible
combinations of 0s and 1s that could occur in the remaining 14 bits produce a total number
of possible hosts that could be assigned in each subnet. Thus, the number of hosts assigned
to each subnet is now 16,382.
In the same Class B network, if 3 bits are borrowed, making the mask 3 bits longer, the size
of the host ?¬?eld decreases from 16 bits to 13 bits, because you borrowed 3 bits to make
subnets, and now the total number of host addresses for each subnet decreases to 8192
(213). The number of usable host numbers decreases to 8190 (8192 ??“ 2). In this Class B
network, for example, the usable subnets created are 6 (23 = 8 ??“ 2), each having 8190
(8192 ??“ 2) usable host addresses. Figure 4-13 shows the number of subnets and hosts that
can be computed in a Class B address space by borrowing host bits.
Figure 4-13 Borrowing Bits in a Class B Network Address Space
Computing Hosts for a Class A Subnetwork
Finally, consider a Class A network address, in which by default 8 bits are used for the
network ID and 24 bits are used for the host ID. Therefore, there are 16,777,216 (224)
possible addresses available to assign to hosts (16,777,214 usable addresses, after
subtracting the 2 addresses, the broadcast and the subnet addresses, that cannot be used).
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