ftp can build data connection - masquerading problem?

[Guilherme Soares Zahn <gzahn@cnen.gov.br>]

Hi there,

    Lately I've been facing a strange and very annoying problem... When
I try to do FTP from a site, it will almost surely drop my connection
out when I try to build a data connection (either through a 'get',
'retr' or just a harmless 'dir') with a message like:

ftp> dir
200 PORT command successful.
425 Can't build data connection: Connection refused

On other systems I've had a 'address already in use' or something, so I
felt it could have to do with the IP Masquerading... I can't say for
sure if it started just after we set our Linux router to do IP
Masquerading or not, but I feel it was 'almost at the same time', so
maybe I've just overlooked something when I did that... HTTP connections
AND apt-get run just fine, though...

Any ideas??

[]'s

Guilherme Zahn