Hello. The documentation says that Multi-User Editing only uses port 6666.In fact, it connects all the time on a random port such as 56725 or another. As and where can be ask concrete port for work Multi-User Editing to his point to in firewall and not leave huge hole in security opening all ports. Thanks.
Concrete port for work Multi-User Editing
I would guess the editor server uses 18.104.22.168:6666 to wait for incomming connections. then it opens random upper udp ports for the connections. I would suggest you to use a vpn and not do this on a normal internet line. then you can do your firewalling based on the communication interfaces.