Content caching when using VPN
We have two iMacs. One of my iMacs accesses the internet through an external VPN. How do I include that computer in content caching for my home network — the public address is different while it's connected through the VPN.
What setup will work if I want both iMacs to cache for each other and for all the iOS devices in the home?
We have one AirPort Extreme and one public IP (except for when the iMac is on the VPN)
iMac 27", macOS 10.14