The Problem: You’re network is 10.1.1.1/24. Subnet: 255.255.255.0 You have 254 usable addresses and let’s say 100 of them are part of the DHCP pool. That leaves you with 154 assignable address. That’s plenty you say. That’s what you say today… Next year you need to expand the DHCP pool to support more users and your new virtual environment consumes 25 address not counting the VMs is runs. Now we are close to running out of address.
The Solution: Expand your subnet to open up more usable addresses. First you must decide how many more address you will need to maintain scalability within reason and avoid doing this again next year 
Use this chart to help determine the appropriate subnet.
The How: These are the steps I took to create minimal impact to the network and the end users.
1. In AD Sites & Services add the new subnet, let it replicate across domain controllers.
2. Update the subnet from 255.255.255.0 on all static network devices (switches, printers, servers, firewalls etc).
3. Update the DHCP settings to handout the new subnet to dynamically assigned devices.
