Freenode and efnet are completely separate. But both freenode and efnet have lots of servers (typically spread out geographically) that are synchronized and it'

Freenode and efnet are completely separate. But both freenode and efnet have lots of servers (typically spread out geographically) that are synchronized and it's between those that a split can occur. People in channel #xyz on efnet doesn't have to be connected to the same server to talk to each other (during normal operation).