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https://issues.apache.org/jira/browse/SSHD-903?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16779724#comment-16779724
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Goldstein Lyor commented on SSHD-903:
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Yes, it is possible to configure WinSCP selected version (see below) - please
note that the *client* is the one that decides on the version - so if it says
{{6}} (as WinSCP does) but the server does not support it, then they cannot
negotiate a version. Therefore, the server cannot "force" the client since
there is no real "negotation" - the client's 1st packet contains its preferred
version. The server can either play along or refuse - either way, there is
exchange of packets back and forth. [Draft
13|https://tools.ietf.org/id/draft-ietf-secsh-filexfer-13.txt] defines an
*extension* than can allow for re-negotiation (which we support). My
interpretation of it is as follows:
* The client asks for version 3 - which is the most supported version
* The server accepts and also returns the extensions it supports
* If the client detects the "versions" extension then it re-negotiates to
version 6 (or whatever other it wants).
!screenshot-winscp-sftp-version.png!
> SFTP version negotiation does not work
> ----------------------------------------
>
> Key: SSHD-903
> URL: https://issues.apache.org/jira/browse/SSHD-903
> Project: MINA SSHD
> Issue Type: Bug
> Affects Versions: 2.2.0
> Reporter: Mark Ebbers
> Priority: Major
> Attachments: screenshot-winscp-sftp-version.png, sftp-version-1.png,
> sftp-version-2.png
>
>
> I have some problems with uploading files to our MINA SSHD based SFTP server
> when using ,different version, of WinSCP as SFTP client. WinSCP is configured
> to use version 6 of the SFTP protocol if possible.
> Uploading a file of ~ 45KB sometimes result in a file of 32711 bytes where in
> the data is not appended (from the second SFTP packet) but overwritten. (But
> did not pin point the exact bug)
> As a temporary solution I found, in issue SSHD-874, a comment which suggest
> to force the server to use sftp-protocol version 3. If I do this I expect the
> server to negotiate with the client that version 3 should be used instead of
> version 6. But what happens is that the server sends a not supported message.
>
> I think that the AbstractSftpSubsystemHelper::checkVersionCompatibility() is
> the problem.
> See my screenshots. As you can see the version proposed by WinSCP is version
> 6. I forced the server on version 3.
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