pfSense

Using FTP through pfSense to a server that uses always the same port for passive data connections only works for the first data transfer.
After bypassing the pfSense the data transfer works as expected.

To reproduce it use vsftpd with pasv_max_port=40000 and pasv_min_port=40000.
After the first data transfer you'll get a timeout for the next attempt.

1. ftp 10.1.1.91
   Connected to 10.1.1.91.
   220 FTP service ready.
   Name (10.1.1.91:root): anonymous
   331 Please specify the password.
   Password:
   230 Login successful.
   Remote system type is UNIX.
   Using binary mode to transfer files.
   ftp> pass
   Passive mode on.
   ftp> ls -l
   227 Entering Passive Mode (10,1,1,91,156,64)
   150 Here comes the directory listing.
   226 Directory send OK.
   ftp> ls -l
   227 Entering Passive Mode (10,1,1,91,156,64)
   ftp: connect: Connection timed out
   ftp> bye
   421 Timeout.