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Jarle Aasland
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 Posted: Thu Feb 19, 2004 6:06 pm Post subject: Delphi FTP/ZoneAlarm problem |
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Using NMFTP (Delphi 5) or Indy FTP (Delphi 7), I have serious problems when
trying to work from a system with ZoneAlarm running. I'm able to connect to
the remote server, but other commands (like list) fails.
Everything works just fine when I first close ZoneAlarm. And yes, the app is
on the ZoneAlarm OK list (Allow everything).
Any suggestions?
Jarle
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Remy Lebeau (TeamB)
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| Posted: Thu Feb 19, 2004 7:17 pm Post subject: Re: Delphi FTP/ZoneAlarm problem |
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"Jarle Aasland" <jaaslan.no.spam (AT) online (DOT) no> wrote
| Quote: | I'm able to connect to the remote server, but other commands (like list)
fails. |
FTP uses two socket connections - one for commands and one for data. LIST
uses the data channel to send the directory listing information. Your ZA is
probably blocking that second connection. This 2-connection design is why
FTP is not firewall-friendly in the first place. Try putting the FTP client
into PASV mode before retreiving the listing.
Gambit
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Jarle Aasland
Guest
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| Posted: Sat Feb 21, 2004 4:54 pm Post subject: Re: Delphi FTP/ZoneAlarm problem |
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"Remy Lebeau (TeamB)" <gambit47.no.spam (AT) no (DOT) spam.yahoo.com> wrote
| Quote: | Try putting the FTP client
into PASV mode before retreiving the listing.
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Unfortunately, this doesn't help. Any other suggestions?
Jarle
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Remy Lebeau (TeamB)
Guest
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| Posted: Sun Feb 22, 2004 5:03 am Post subject: Re: Delphi FTP/ZoneAlarm problem |
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"Jarle Aasland" <jaaslan.no.spam (AT) online (DOT) no> wrote
| Quote: | Unfortunately, this doesn't help. Any other suggestions?
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You need to make sure that the appropriate ports are open in the firewall.
When a client runs in PASV mode, the FTP server opens a second server socket
that the FTP client connects to when receiving data from the server. When
in non-PASV mode, the FTP client opens its own server socket instead that
the FTP server connects to when sending data to the client. Either way,
whichever port the client or server is listening on, that port needs to be
open in the firewall, which is not always easy to know ahead of time. As I
said earlier, the FTP protocol is not firewall friendly for exactly this
reason.
In the case of ZoneAlarm, if you have your client program configured to
allow all outgoing connections, then PASV mode should have worked fine since
the client is establishing a second outgoing connection to the same server,
and ZoneAlarm works on program permission policies, not specific port
numbers (although it can be set up for that as well). You need to check
ZomeAlarm's logs to find out whether it blocked the connection or not.
Gambit
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