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I have two machines on the same ethernet network segment:

  1. VM running Windows Server 2012R2 [sftp client]
  2. Physical server running Ubuntu 16.04.7 LTS [sftp server running openssh-server 1:7.2p2-4ubuntu2.10]

When I establish an SFTP connection from the windows VM to the ubuntu server, when I try to list the files in a directory that has a large number of them, the connection hangs. Folders with small numbers of files work fine.

If I try the same thing using a different Ubuntu 16.04.7 machine as the client, it works fine.

Also tried a max size ping using ping -l 1472 -f and that worked correctly.

Things I have tried that didn't change the outcome:

  1. multiple SFTP clients on windows: PuTTY 0.74, WinSCP 5.17.9, and FileZilla 3.52.0.5
  2. lowering the MTU on the windows VM [default 1500]
  3. lowering the MTU on the ubuntu server [default 1500]
  4. updating the vmxnet3 ethernet driver from 1.8.16.0 to 1.8.17.0
  5. using a different Windows Server 2012R2 VM as the client
  6. using a Windows Server 2016 VM as the client
  7. using a Windows Server 2016 physical machine as the client

I'm now stumped. Any ideas or suggestions for further troubleshooting?

JoeNahmias
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1 Answers1

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Well, I was in the middle of writing up a bug report for the PuTTY folks and was reviewing the /etc/ssh/sshd_config on the Ubuntu 16.04 server. It had the line:

Subsystem sftp internal-sftp

I changed it to:

Subsystem sftp /usr/lib/openssh/sftp-server

restarted sshd and now everything works properly!

JoeNahmias
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