Access to your CDN zone and respectively to your assets can be limited to an IP address or to an IP network. You can either define a list of disallowed IP addresses/IP networks, or a list of allowed ones.
To limit the access to your CDN zone by an IP address/IP network, follow the steps outlined below:
1. Log in to the Universal CDN Control Panel at my.ucdn.com.
2. Navigate to the My Zones tab located in the top left corner.
3. Click on the cogwheel icon 
next to the CDN Zone which access will be restricted.
4. Navigate to the Limit Access tab.
5. Scroll down to the Limit access by IP feature and check the box next to it.
6. From the drop-down menu select to allow or to prohibit access from specific IP addresses or IP networks.
The IP addresses or IP networks must explicitly list each IP address.
The maximum number of records you can have for either allowed or blocked IPs is 64.
After making any changes in the Universal CDN Control Panel do not forget to click on the Save Changes button.