The filibuster appears nowhere in Robert’s Rules. It is a legislative concept peculiar to the US Senate. So, Robert’s has no rules on filibuster. That said, I believe that the speaker may “hand off” to another speaker who he/she recognizes. That may not be true. The purpose, of course, is to totally tie up/stop any further business as long as the speaker holds the floor.
that, i think, is the part i am not sure about- I thought anyone who has the floor can hand it off to anyone else