What URL/IP + Port do I need open (at the firewall) in order to synch the Greenbone Community Feeds with my OpenVAS scan server?

I am using Greenbone Community (not the paid version). Thank you!

The greenbone-feed-sync GitHub README.md page shows the default URL for the community edition feed is rsync://feed.community.greenbone.net/community. So, that requires IP and port 873.