FTP error 426 ( active mode or Passive mode )

Question

I have a user report FTP error 426. Can anyone tell me ahwt situation would lead to that error ?

I habe 'googled' for som advice on it, but the only area where there is come relevamnt discussion relates to passive vs active mode ? Could that be an issue ? and in a more general sense when should active vs passive mode be used ?

Thanks,

Martin

Answer 1

Usually, error 426 occurs when a data connection is broken or closed improperly. The reasons for this can vary - for example, some versions of ActiveSync were observed to cause this problem quite often and some users reported that to be a common problem (we believe this discussion is also related), although the majority of our customers don't seem to suffer from it. What version of Rebex FTP do you use? A full 426 error message might also provide additional information, and a communication log produced using Ftp object's LogWriter property might help as well.

In case this error occurs when uploading a file even though the file has been fully uploaded, a EnableImproperDataCloseWorkaround workaround (available in the latest release of Rebex FTP) can be enabled to get rid of it:

C#:

ftp.Options |= FtpOptions.EnableImproperDataCloseWorkaround;

VB.NET:

ftp.Options = ftp.Options Or FtpOptions.EnableImproperDataCloseWorkaround

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Regarding active and passive mode: Active mode requires the FTP server to establish a connection to the FTP client. This was perfectly acceptable in the 1980s when there was no need for any firewalls and all FTP servers were connected directly to the Internet. But now this approach is outdated and requires complicated FTP-aware firewalls to be able to function. Many firewall and NAT devices don't even support it at all. ActiveSync doesn't support it either. Many cell phone providers don't support it.

Generally, it only makes sense to use active mode when the network policy at the client is very permissive (=security is weak) and the network policy at the FTP server makes passive mode FTP impossible (which is very rare).

Comments

Lukas, Thanks for your answer. The error is after an aparently good transfer. ActiveSync is involved, but may not be when the solution is fully rolled out. If the error persists, I shall add logging etc to get more information. What version is required for the EnableImproperDataCloseWorkaround option. I have FTP for .Net CF 2.0 ( v2.0.2567 ). Where can I found out if I am eligable for an upgrade, or where the upgrade costs are please ? many thanks Martin

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Martin, the EnableImproperDataCloseWorkaround option is included in version 3.0.3793.0 released at 2010-05-20 http://www.rebex.net/ftp-ssl.net/history.aspx#3793 . You'll see a status of your support contract and will be able to renew it at http://www.rebex.net/protected/ . I've also sent upgrade details to your email.

Answer 2

This method seems to be missing from the latest version

ftp.Options = ftp.Options Or FtpOptions.EnableImproperDataCloseWorkaround

Comments

Please note that the FtpOptions.EnableImproperDataCloseWorkaround is present only in .NET CF version.