Path in CC5: System Settings - Access Control - Whitelisting
By default, the system is configured with whitelisting disabled, which means that logins from all IP addresses will be accepted. Your public IP address is displayed under the Whitelisting tab. And the checkbox Allow all IP addresses is ticked.
Some business choose however to restrict access by whitelisting the IP addresses that shall have access. In this case, the checkbox Restrict valid IP addresses must be ticked. The whitelisted IPs are then listed in the table below. New IPs can be added via Add new IP range.
Read more here.