Use a site like http://whatismyipaddress.com/ or http://whatsmyip.org/from your mining machine to find out your public ip and try using this address. If your mining machine is a headless linux box you can use the following command: curl ifconfig.co . Also make sure that your are actively mining on the pool and your miner is submitting valid shares.
You must enter the IP address that ends with the digits given in the interface. For example if the system is asking for ip *.*.*.212 than you need to enter your ip address that ends with 212 (in case you mine from multiple different IP addresses).