9.2 Creating Subnets
9.2.3 Sample problems
Problem 1:
Network Address:
172.25.0.0
Requirement: Need 600 hosts per subnet

Solution:
Subnet Mask needed: 255.255.252.0
Reason: :252 in the third octet leaves 10 bits for the hosts or 1022 hosts per subnet. 255.255.248.0 would have been more hosts than we needed and 255.255.254.0 would not have been enough hosts.

Problem 2:
Network Address:
172.25.0.0
Requirement:
Need 8 subnets with the greatest number of hosts possible per subnet

Solution:
Subnet Mask needed:
255.255.240.0
Reason:
255.255.240.0 will give you 14 subnets. 255.255.224.0 will not be enough subnets and 255.255.248.0 will not provide the maximum number of hosts per subnet.