The Caching Server in OS X is a little bit of a black box. But, it’s not all that complicated, compared to some things in the IT world. I’d previously written about command line management of the service itself here. When you enable the caching service, the server registers itself as a valid Caching Server. Nearby devices then lookup the closest update server with Apple and register with that update server using a GUID: /Applications/Server.app/Contents/ServerRoot/usr/sbin/serveradmin settings caching:ServerGUID Then, each time the device looks for an update, it does so against http://mesu.apple.com/assets/com_apple_MobileAsset_SoftwareUpdate/com_apple_MobileAsset_SoftwareUpdate.xml using the device model. Noticed this with this line in my proxy logs: "GET http://mesu.apple.com/assets/com_apple_MobileAsset_SoftwareUpdate/com_apple_MobileAsset_SoftwareUpdate.xml HTTP/1.1" 200 - "-"…