If you wish to restrict access to your eFront system so that your users may be able to access it from specific IPs only, log in to your system as an administrator and from your Administration dashboard navigate to 'System Settings', then visit the 'Security' section (1).

Through the General tab (2) you will be able to view the Allowed IPs text field (3).

In this field you may insert a comma-separated list of IPs (you may use the * asterisk wildcard for a whole set of IPs) to register the allowed IPs for your system, meaning that only users logged in from that IPs will have access to your system.