This is about Application > Incoming Security > Client Restrictions > Only allow publishing from the following IP addresses.
Every time you add/remove an IP address to/from this list, you must restart the application. It would be good if this list could be edited without having to restart application, because it means all streams get a short breach. And in case of .stream files, one must restart the streams manually (since only restarting the entire Server calls StartupStreams.xml)
Actually, the more we can avoid restarting an application, the better; that counts for other settings too. Maybe some changes won't apply to existing connections until restarted, but at least they'll be applied to new connections.