Topic on Project:Support desk

I have my own wiki farm, multiple wikis, and I would like to enable it so that when I search for something on a wiki on the Special:Search -special page, it shows similar results from other wikis. We have CentralAuth up and running and the wikis are connected.

What setting should be on for the search function to show results from other connected wikis?

The wikimedia version is part of extension:CirrusSearch but prob requires additional setup i dont know about.