OS X Server allows you to configure a local Software Update server so that workstations on your network can download and install Apple software updates from your local server instead of Apple's public Software Update service.
Requirements for hosting a software update server
The Software Update service requires that the server is registered in DNS (Domain Naming Service) and resolves correctly. The DNS name of the server is used by the clients to download updates.
Servers and ports
The synchronization module accesses the following public Software Update servers on destination port 80:
The latter (http://swcdn.apple.com) currently redirects to the Akamai content distribution network that hosts the updates. Note that the redirected IP address of http://swcdn.apple.com may vary over time or by geographic region.
With OS X Mountain Lion v10.8 or later, the synchronization module also accesses the following public Software Update server on destination port 443:
Authenticated proxy servers are not supported by the synchronization module, which means updates will not be mirrored by the server. While the synchronization module may work with non-authenticated and transparent proxy servers, Apple recommends that the Software Update server have direct access to the public Software Update servers listed above.
Dedicated network connection to the Internet
Software Update Server requires that the server have a dedicated connection to the Internet (specifically, to the URLs listed above in the "Servers and ports" section). If Software Update Server is unable to reach Apple's content servers within the default HTTP connection timeout, it will try again during the next scheduled sync, 24 hours later.