The Caching Service updates it's registration with Apple every 55 minutes, as registrations expire on Apple's side after 1 hour. This mechanism not only allows for a crashed Caching server to be removed from registry but also to track changes in the public IP.

Changing the Only cache content for local networks setting causes an immediately re-registration, removing the local network range from the registration payload when the setting is turned off.

On Stop
When the Caching Server stops it deregisters with lcdn-registration.apple.com allowing clients to download updates from Apple servers again.