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List:       mina-dev
Subject:    [jira] [Created] (SSHD-1292) Connection problem with Rebex Buru SFTP Server
From:       "Roberto Deandrea (Jira)" <jira () apache ! org>
Date:       2022-08-26 14:47:00
Message-ID: JIRA.13478836.1661525167000.206467.1661525220004 () Atlassian ! JIRA
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Roberto Deandrea created SSHD-1292:
--------------------------------------

             Summary: 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


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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