problem with pasive MODE and NAT

["Francisco Castillo" <fcastillo@hostgreen.com>]

Hello,

I has a proftpd server on a linux debian woody with a NAT sheeme. So my
proftpd is listening on the 192.168.0.X private ip and my router has
mapping the ports from 40000 to 40010 from the public ip to the
192.168.0.X ip in order to allow pasive port transfers from internet. So
i has this config on my proftpd.conf

....................
# para el NAT
MasqueradeAddress       217.00.00.214
PassivePorts 40000 40010        # These ports should be safe


but i has this problem:

when i connect from a cuteftp client from a 192.168.0.Y ip the client get
the correct pasive port to get data (40000) from the proftpd server but
if i try to access from a public client ip (with cuteftp too) the server
said to get a aleatorious port and not in the range 40000-40010
COMANDO:>        PASV
        227 Entering Passive Mode (217,00,00,214,238,235)).


238,235 = 238*256 + 235 != 40000-40010

so i ask

what could be happening?
How could i solve my problem?

Thanks in advance.
Francisco.