You can ask NetSuite, but may not get the information. Years ago I tried to get a list of possible IP addresses from NetSuite so we could whitelist them in a public API's firewall rules. I was basically told that they would not release that information to me because it could change or become outdated at any moment. We had to design our public api differently to allow requests from any IP address to the specific URL's that my NetSuite scripts would be calling.