Hello @dolanduck. ,
in modern classless routing you can also perform supernetting that actually means going above the classful network limit creating a prefix like 192.168.0.0/16.
However, with some routing protocols like RIPv2 this is possible but with great limitations. There are no issues with OSPF or EIGRP.
To answer you question you need to note the following:
300 hosts > 254 --> requires 9 bits /23 subnets that can host up to 510 hosts.
To be able to have 200 of /23 you need a /15 prefix so even 192.168.0.0/16 is not enough as it is able to accomodate only 128 /23 subnets.
You would need 192.168.0.0/15 to accomodate 200 /23 subnets.
>>
My second question is do you need a sub-net mask to find sub-nets and host bits in a network.?
like if i only have 172.0.0.0 or 192.168.0.0 but no mask is it possible ?
Generally speaking yes you need additional information that can be a subnet mask or a number of end user hosts that must be supported to be able to find the right subnet size like in the exercise above.
The rule is that N host bits allow to accomodate 2^N -2 hosts ( one is the subnet and the last is the subnet broadcast address).
P+ N = 32
where P is the prefix length
and N needs to be able to satisfy the disequation 2^N-2 > MAx hosts per subnet
Where N is the smaller one that satisfy the above condition.
Hope to help
Giuseppe
