"425 Can't build data connection: Address already in use" with FTP

[Minoru Asano]

Hello,

When we communicate with same Tru64 UNIX by using FTP,
the following messages has appeared:
"425 Can't build data connection: Address already in use."

[ENVIRONMENT]
Tru64 UNIX V4.0G and V4.0F
There is firewall between two Tru64 UNIX.

[SITUATION]
We execute FTP between V4.0G and V4.0F, and there is firewall between two systems.
This trouble appeared ONLY two time from building this system.

The following are part of FTP log:
............................
---> TYPE A
200 Type set to A.
---> PORT xxx,xx,xxx,xxx,17,41
200 PORT command successful.
---> LIST XXXXXXXX*
425 Can't build data connection: Address already in use.
---> PORT XXX,XX,XXX,XXX,18,186
---> NLST XXXXXXXX*
XXXXXXXX*: No such file or directory.
can't find list of remote files, oops
..............................

[QUESTION]
- Why "Address already in use" message appear using FTP ?
- How can I avoid this trouble ? Is there any preventive measures ?

Thank you for advice.
Best Regards.
/Minoru.

[Rob Leadbeater]

Hi,

The first PORT command listed above is trying to set up the data connection on port 4393. (17*256 + 41).

Check you haven't already got something listening on that port (netstat -an).

Or maybe your firewall is blocking some of the ports required for Active FTP...

This site gives a good example of the ports you may need to have open:

http://slacksite.com/other/ftp.html

Hope this helps,

Regards,

Rob

[Minoru Asano]

Hello,

Thank you for reply and information.

May I ask a question ?

If this trouble happen due to port which is already use, what shall I do to prevent this trouble ?
Is it related to passive mode and active mode ?

Thank you for advice.
Best Regards.
/Minoru.

[Ivan Ferreira]

>>> Is it related to passive mode and active mode ?

Yes.

>> If this trouble happen due to port which is already use, what shall I do to prevent this trouble ?

Use passive mode for data transfers or open your firewall to allow incoming connections. See:

http://slacksite.com/other/ftp.html

[Minoru Asano]

Hello,

Thank you for quick reply and suggestion.

May I ask some question again ?

- How can I confirm whether passive or active mode ?

- How can I set passive mode ?

Thank you for advice.
Best Regards.
/Minoru