Ports for Passive mode

I read in the docs that ports 50000-50009 are used and must be opened in the router for passive mode. But when I do that, connection fails, and in the log I see the line:

Opening passive mode data connection to 132.236.21.62, port 49247.

If I open 49000-50009, everything works, but I don't want to open more ports than necessary. Which ones are required? For the connection itself I use 23 (21 is not available).

Thanks for any tips!

Slava