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SCP file transfer from Windows 10 Command prompt to Mac Big Sur looks like it didn't transfer anything, but it is actually transferring exactly 16KB before the connection is lost (see image below). Files under 16KB work fine. Files over 16KB, like this one, always transfer exactly 16384 bytes and then the connection is lost. Any ideas?

Command prompt scp transferring only 16KB

I added -vvv to my scp client invocation. Below is that. (It doesn't look helpful to me -- Error:10054.) I've also captured sshd debug output from the Mac side. I put that here (link). I'm not sure what to make of that either.

scp -vvv
...
debug3: send packet: type 50
debug2: we sent a keyboard-interactive packet, wait for reply
debug3: receive packet: type 60
debug2: input_userauth_info_req
debug2: input_userauth_info_req: num_prompts 1
debug3: failed to open file:H:/dev/tty error:3
debug1: read_passphrase: can't open /dev/tty: No such file or directory
Password:
debug3: send packet: type 61
debug3: receive packet: type 60
debug2: input_userauth_info_req
debug2: input_userauth_info_req: num_prompts 0
debug3: send packet: type 61
debug3: receive packet: type 52
debug1: Authentication succeeded (keyboard-interactive).
Authenticated to 10.240.0.25 ([10.240.0.25]:22).
debug2: fd 4 setting O_NONBLOCK
debug2: fd 5 setting O_NONBLOCK
debug1: channel 0: new [client-session]
debug3: ssh_session2_open: channel_new: 0
debug2: channel 0: send open
debug3: send packet: type 90
debug1: Requesting [email protected]
debug3: send packet: type 80
debug1: Entering interactive session.
debug1: pledge: network
debug3: receive packet: type 80
debug1: client_input_global_request: rtype [email protected] want_reply 0
debug3: receive packet: type 91
debug2: channel_input_open_confirmation: channel 0: callback start
debug2: fd 3 setting TCP_NODELAY
debug2: client_session2_setup: id 0
debug1: Sending command: scp -v -t ~/BrokerTEST.zip
debug2: channel 0: request exec confirm 1
debug3: send packet: type 98
debug2: channel_input_open_confirmation: channel 0: callback done
debug2: channel 0: open confirm rwindow 0 rmax 32768
debug2: channel 0: rcvd adjust 2097152
debug3: receive packet: type 99
debug2: channel_input_status_confirm: type 99 id 0
debug2: exec request accepted on channel 0
Sending file modes: C0666 1599823 Broker.zip
debug2: channel 0: rcvd ext data 31
Sink: C0666 1599823 Broker.zip
debug2: channel 0: written 31 to efd 6
Broker.zip                             0%    0     0.0KB/s   --:-- ETA
debug3: ERROR:10054, io:0000023350337930
Connection reset by 10.240.0.25 port 22
lost connection

With some further testing, I was able to successfully transfer the same file using the same command to a different Mac. So, I started suspecting the Mac side, but...

With yet more testing, it is likely the routing between the Windows box and the Mac. The Mac giving me trouble is in the server room at my work. The other Mac and my Windows machine are behind a Meraki router at my home configured for me with a VPN in to the office. I was able to successfully transfer the file from a different Windows VM at work to the Mac at work. So, it doesn't appear to be the Mac, but the routing between my home and my work.

Interestingly, I'm able to reproduce the issue from a VM at our Ohio site, almost. The only difference is transferring from there (to the same Mac at my Wisconsin office) isn't always cut off at 16,384 bytes. It isn't consistent how many bytes it gets cut off at. As I said above, whenever I test from my Windows box at home to the Mac, the transfer always cuts out at 16,384 bytes exactly, every time, every file I test. From the Ohio VM, one transfer got cut off at 246KB, another was at 147KB, another at 115KB. Otherwise, I'm seeing all the same symptoms. I'm not sure how the VPN between the sites is set up, but it seems to have a similar issue.

Thanks for any help you may be able to provide!

-Matt

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    Can you add -vvv to your scp client invocation in Windows 10 and also to the way sshd is invoked on your Mac, the reproduce the problem and edit your Question to add the verbose scp/sshd logs? When troubleshooting ssh-related problems (including scp), the first step is often to crank up the verbosity of the logs on both the client and server process and see what you can learn from the verbose logs.
    – Spiff
    Dec 24, 2020 at 2:03
  • Thank you, @Spiff. I added -vvv output in Command Prompt in Windows and included that output. That was easy enough. I don't know how to do that on the Mac side, though. Any help there would be appreciated. Dec 24, 2020 at 3:32
  • Just for giggles, can you try it without the `~/
    – Spiff
    Dec 24, 2020 at 4:40
  • @Spiff, It won't let me write to the root. I changed it to "/users/developer/BrokerTEST.zip" instead of "~/BrokerTEST.zip" (the same location) and I get the same result. I also tried "/tmp/BrokerTEST.zip" and I get the same result there, also. Dec 24, 2020 at 6:04
  • @Spiff, I added output I captured on the Mac side to the question now, too. I don't know the best way to do that but I followed what was suggested in the following answer to another question. stackoverflow.com/a/54148031/604962 Dec 24, 2020 at 6:42

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