Scalability and storage of cached content for Apple devices
By default, content caching is limited to a specific subnet, but you can set it to provide content caching for:
All combinations of subnets of the local network that share a common public IP address
Any combination of subnets of publicly accessible IP addresses (with additional DNS setting support)
If your network has multiple subnets that share the same public IP address, all the subnets can take advantage of a single content cache.
When your network has more than one content cache, the content caches automatically become peers and can consult and share cached software. When a requested item isn’t available on one content cache, it checks its peers for the item. If the item is available, it’s downloaded from the peer. If it’s not available, the content cache downloads the item from one of its parents, if any are configured, or from Apple through the internet. Clients automatically select the right content cache when more than one is available.
The default location for cached content is the boot volume. You can choose an alternate location and specify how much of the volume is used by content caching. When the storage space for the cached content reaches the maximum you specified, or when the available space on the volume runs low, the content cache deletes content that hasn’t been used recently to make space for the next request.