In order to protect your network from ransomware, you need to constantly monitor and verify who has access and who is in your network at all times. This can be achieved through network monitoring and security applications that send alerts whenever suspicious activity is detected. You also need to make sure all of your software, anti-virus, firewall and security applications are up-to-date.
Educating employees so that they know not to click on links in suspicious emails or download any questionable attachments is important as well. They should also not be able to add or download new applications to the server without the prior consent of IT. All applications utilized in an organization need to be whitelisted by IT in order to prevent ransomware attacks.