Hello Deepa - thanks for your question, please check out this document in our on-line help:
This will show you the IP addresses / DNS names you can whitelist in your environment to prevent nu-authorized access to your data source from any other client.
There are few things to consider - remember Qlik access the data on load only - which is done on demand using a button in the data manager - or when scheduled. Once the data is loaded into the app - it becomes part of the app - and no longer has a live connection to the underlying source (unless reloaded)
So by whitelisting the IPs / DNS names you are preventing other outside access - and only allowing Qlik Sense Cloud to access that URL.
Let me know if you have any other questions.
When applicable please mark the appropriate replies as CORRECT. This will help community members and Qlik Employees know which discussions have already been addressed and have a possible known solution. Please mark threads as HELPFUL if the provided solution is helpful to the problem, but does not necessarily solve the indicated problem. You can mark multiple threads as HELPFUL if you feel additional info is useful to others.