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https://issues.apache.org/jira/browse/SSHD-1292?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17601969#comment-17601969
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Thomas Wolf commented on SSHD-1292:
-----------------------------------
It's not possible for me to deduce anything about possible underlying causes
from this.
* I don't know why SSH authentication would fail _sometimes_.
* "delaying write until window space is available" is a debug message, it
doesn't indicate any problem.
* I cannot speculate about reasons for the SFTP server sending ignore messages.
You probably have a local installation of the Rebex SFTP server, so you have
access to both the server's and client's debug logs. It should be possible to
figure from those logs on which side the problem might be., and perhaps even
what the problem is.
For the client I would suggest to try with the newest Apache MINA sshd 2.9.1.
There were [quite a
few|https://github.com/apache/mina-sshd/blob/master/docs/changes/2.9.0.md]
[changes|https://github.com/apache/mina-sshd/blob/master/docs/changes/2.9.1.md]
since 2.8.0, including some bug fixes that just might have something to do with
your problem.
> Connection problem with Rebex Buru SFTP Server
> ----------------------------------------------
>
> Key: SSHD-1292
> URL: https://issues.apache.org/jira/browse/SSHD-1292
> Project: MINA SSHD
> Issue Type: Question
> Affects Versions: 2.8.0
> Reporter: Roberto Deandrea
> Priority: Major
>
> Hi Thomas,
>
> I have connection problems with a Microsoft SFTP server called Rebex SFTP
> Server
> ([https://www.rebex.net/buru-sftp-server/).|https://www.rebex.net/buru-sftp-server/)]
> This is a NEW connection setup for our SFTP client/server product.
>
> I have SFTP client based on Apache SSHD 2.8.0. The client is configured for
> pushing files to the Rebex SFTP server.
>
> Description of the problem :
> Sometimes the SFTP client is unable to push files on this remote SFTP
> Server, the SSH handshake fails during SSH handshake for an authentication
> timeout set to 60 secs that expires.
> The exception is the following :
> {quote}Caused by: org.apache.sshd.common.SshException:
> DefaultAuthFuture[ssh-connection]: Failed to get operation result within
> specified timeout: 60000
> at
> org.apache.sshd.common.future.AbstractSshFuture$$Lambda$284/0000000000000000.apply(Unknown
> Source)
> at
> org.apache.sshd.common.future.AbstractSshFuture.formatExceptionMessage(AbstractSshFuture.java:185)
> at
> org.apache.sshd.common.future.AbstractSshFuture.verifyResult(AbstractSshFuture.java:111)
> at
> org.apache.sshd.client.future.DefaultAuthFuture.verify(DefaultAuthFuture.java:39)
> at
> org.apache.sshd.client.future.DefaultAuthFuture.verify(DefaultAuthFuture.java:32)
> at
> org.apache.sshd.common.future.VerifiableFuture.verify(VerifiableFuture.java:56)
> at com.primeur.sshd.client.SSHDClient.connect(SSHDClient.java:157)
> {quote}
>
> When the connection fails, looking through the verbose logs of the client I
> sometimes found :
> [8/23/22 6:35:52:064 EDT] 0000bfcb id=00000000
> org.apache.sshd.common.channel.ChannelAsyncOutputStream 1 doWriteIfPossible
> doWriteIfPossible([SftpChannelSubsystem[id=0,
> recipient=0]-ClientSessionImpl[StateStreet@/127.0.0.1:40787][sftp]]
> cmd=SSH_MSG_CHANNEL_DATA) *delaying write until space is available in the
> remote window*
> This trace seems to evidence some issues writing data on socket according to
> SSH protocol....
> I've managed to handle this warning "delaying write until space is available
> in the remote window{*}"{*} setting the system property
> *-Dorg.apache.sshd.config.sftp-chunk-if-window-less-than-packet=true*
> without any improvement.
>
> The authentication timeout expires because the SSH messages related to client
> authentication are not sent and received between client and server.
>
> +Q. What do you think about this log ?+
>
> [8/23/22 6:35:52:285 EDT] 0000bfcf id=00000000
> common.session.helpers.ReservedSessionMessagesHandlerAdapter 1
> handleIgnoreMessage
> handleIgnoreMessage(ClientSessionImpl[StateStreet@/127.0.0.1:40787])
> *SSH_MSG_IGNORE*
>
> The receiving of some *SSH_MSG_IGNORE* messages from SFTP remote server could
> mean that the socket connection is in idle state and no data flow on the
> socket.
> +Q. Can you confirm ?+
>
> Q. Do you think that this issue is caused by external factor (i.e network
> latency/load, firewalls, balancers etc..... or is caused by some tricky SSH
> implementation details or interoperability issues with this SFTP server (less
> likely...) ?
>
> Thank you in advance for your cooperation.
> Regards, Roberto.
>
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