LIST fails on some locations

Questions dealing with specific FTP clients and Cerberus FTP Server.
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Jack Duijf

LIST fails on some locations

Post by Jack Duijf » Mon Nov 22, 2004 1:12 pm


I experience a strange behaviour when trying to connect to my Ftp-Server
With local connect (, and access via a dial-in Internet connection, there are no problems.
However, from my office using ADSL connection, i can login but the LIST reply does get no reply from the FTP server.

Any suggestions?

Jack Duijf

Posts: 656
Joined: Mon Aug 18, 2003 4:00 am
Location: Denmark

Post by mdj » Wed Nov 24, 2004 8:32 am

Sounds like there is a router/firewall in between on your ADSL line, that doesn't allow the data link to be created. The control link made to the ftp server is to the server's port 21, and that's fine, but the data link is either
A: (non-passive) going from the server's port 20 (usually) to a "random" port on the client - and that looks supicious to the client's router/firewall, or
B: (passive) going from the client to a "random" port on the server - and that looks suspicious to the server's router/firewall (see for further information).
So, if one of the routers/firewalls involved is not ftp-aware, or not explicitly set up to allow the data link, it is blocked. Have a look in the "Firewall Help" forum. I don't know how to set up your router/firewall, or which one is the problem, but perhaps someone else has already solved a similar problem.
Morten Due Jørgensen

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