Subnetting Tricky Questions

From Odom Cisco Press Book:

Subnetting design requires 200 subnets and 120 hosts/subnet.
Single mask be used.
20 percent growth taken into account.

1. 10.0.0.0/25
2. 192.168.7.0/24
3. 172.16.0.0/23
4. 10.0.0.0/22

Answer is 10.0.0.0/22

200 subnets and 120 hosts

240 subnets after twenty percent growth
144 hosts per subnet after twenty percent growth

10.0.0.0/25  does not supply the requisite amount of hosts
as now /25 hosts are 2^7 =128 with 20% growth we need 144
which is not possible.


192.168.7.0/24     No as only one subnet is possible,class C and mask /24

172.16.0.0/23   No as subnets are 2^7 = 128  class B


10.0.0.0/22  Subnets = 2^14 or 16384 subnets and
                    Hosts  = 2^9 =512-2 = 510
                    This works meets both requirements of 240 Subnets
                    and 144 Hosts per subnet , that is with 20% growth.