what does 'per subnet' means then ?

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+13 votes

If a class $B$ network on the Internet has a subnet mask of $255.255.248.0$, what is the maximum number of hosts per subnet?

- $1022$
- $1023$
- $2046$
- $2047$

+25 votes

Best answer

a number of zeros are to be counted for calculating the total number of possible hosts per subnet.

$255$-$248$ = $7$ can be represented using $3$ $bits$

these $3$$bits$ + $8$$bits$ more = $11$ $bits$

So, possible subnets $= $2$^{11}$ out of these $2$ are reserved as subnet $ID$ and $DBA$

Therefore, we have maximum possible usable hosts = $2^{11}-$2$ = 2046$

$255$-$248$ = $7$ can be represented using $3$ $bits$

these $3$$bits$ + $8$$bits$ more = $11$ $bits$

So, possible subnets $= $2$^{11}$ out of these $2$ are reserved as subnet $ID$ and $DBA$

Therefore, we have maximum possible usable hosts = $2^{11}-$2$ = 2046$

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