I tried to make that work, but it didn't seem to do anything. Repeat downloads took just as long as before.

you can verify if Content Cache is working in a couple ways... first, while installing the update, you should see a CPU usage spike in Activity Monitor for the process "AssetCache".

secondly, you can run this command on the machine you want to upgrade, to verify that it can see your Content Caching Server (it should report the local IP address of the machine you set up Content Caching on) "AssetCacheLocatorUtil"

great info, thanks.

Looks like if the machine is asleep it won't use it for a content cache, even if "wake for network access" is turned on. So a pretty useless feature if you have a machine that's allowed to sleep.

If you've just turned on Content Caching, or the machine running it has rebooted, client devices will not discover the server immediately. You need to wait a while, or reboot the client devices, which will force them to discover it.