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https://issues.apache.org/jira/browse/NET-363?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13004682#comment-13004682
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Damon Dan commented on NET-363:
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Yes, I confirm that your changes work. I tested it on the original situation
where the FTP server is behind a NAT firewall and provides a private address.
I also tested it on another FTP server that is on the same private address as
the FTP Client. I assume your patch has special code to handle this situation
because it works OK. The only other place that it might fail would be from one
private network to another - different network. Say, from 192.168.xxx.xxx to
10.xxx.xxx.xxx. I can imagine a scenario where it might cause a failure, but
it seems remote.
> Can't connect to a server behind firewall in passive mode
> ---------------------------------------------------------
>
> Key: NET-363
> URL: https://issues.apache.org/jira/browse/NET-363
> Project: Commons Net
> Issue Type: Bug
> Components: FTP
> Affects Versions: 2.2
> Environment: Windows Client with Zos mainframe server behind a
> firewall. However I think any client/server will demonstrate the issue as
> long as the server is behind a firewall.
> Reporter: daniel damon
> Priority: Blocker
> Fix For: 3.0
>
>
> When the FTP server is behind a firewall, FTPClient can connect, but it
> cannot transfer data. This is because the FTP server provides it's own
> address instead of the firewall address to make the connection. I have
> confirmed the problem by hacking a copy of FTPClient to set the __passiveHost
> to the appropriate internet address. With this hack, I can transfer data.
> Perhaps the FTP server could be configured differently to fix the issue.
> Unfortunately, I do not have access to the server configuration. I do know
> that the commercial product IpswitchFtp does deal with the issue as this
> extract from it's log shows:
> ------------
> PASV
> 227 Entering Passive Mode (192,168,13,11,195,129)
> connecting data channel to 192.168.13.11:195,129(50049)
> Substituting connection address 159.106.121.79 for private address
> 192.168.13.11 from PASV
> data channel connected to 159.106.121.79:195,129(50049)
> LIST
> 125 List started OK
> transferred 4157 bytes in 0.078 seconds, 425.688 kbps ( 53.211 kBps),
> transfer succeeded.
> 250 List completed successfully.
> QUIT
> ----------------------------
> I can take a shot at a fix if you want. I'll set some timeout, and if that
> fails, I'll use the original address
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