Currently under Settings:Edit Extension:Advanced:IP Restriction you are only allowed to enter an IP address with a subnet mask.
CASE: A customer's extension on our S50 was compromised. The hacker proceeded to rack up several hundred dollars of calls before the breach was detected.
Turning on IP restriction would have prevented them from connecting as an extension with the compromised password as it would not have matched the IP criteria.
Most of our remote customers are using connections to the internet that are dynamic and subject to change at random.
In most cases we are able to set up DDNS on the customer site to keep track of the IP they are coming from. Unfortunately, we are unable to enter this DDNS information as a domain under the IP Restriction setting due to being limited to only IP addresses and a subnet mask.