When uploading new website media assets, you can choose between the http & https protocols. The URL field has validation checks and does not accept internal URLS that don't have a domain extension.
IP address is a workaround but not suitable in circumstances where servers are load balanced and could be offline for maintenance. Our companies internal application will also not function if using the IP address.
There should be a "Custom" protocol that will allow us to bypass the validation checks.
Currently the only way we can add our internal sites is via the legacy UI