Controlling SO_RCVBUF

[Darren Tucker]

On Thu, 12 Dec 2019 at 11:16, Robinson, Herbie <Herbie.Robinson at stratus.com>
wrote:

> I have a customer who is complaining about slow SFTP transfers over a long
> haul connection.


Sending, receiving or both?  What's the speed and RTT on the link?

  The current transfer rate is limited by the TCP window size and the RTT.

[...]

> I was thinking about coding a much more modest enhancement that just does
> SO_RCVBUF for specific subsystems.


I don't understand what you're getting at.  If your limiting factor is
really the TCP BDP that's between the ssh and sshd process, and that's
independent of subsystem.

  In the interest of adding something that the OpenSSH community would take
> back into the source base, what do people think is a better fit in the
> configuration file?
>
> A single keyword for specifying connection options:
> SubsystemOptions <subsystem-name> [command-line-option...]
> The subsystem name would be scp, sftp-server, etc.


There is no scp subsystem.


>   The command line options would be -r <n> or --rcvbuf <n> to allow one to
> specify the number passed to SO_RCVBUF.  This would allow one to easily add
> other options (like SO_SNDBUF support).
>

If you're talking about the client side you could implement whatever you
want in a ProxyCommand dialer then possibly pass the open fd back
via ProxyUseFdpass.

-- 
Darren Tucker (dtucker at dtucker.net)
GPG key 11EAA6FA / A86E 3E07 5B19 5880 E860  37F4 9357 ECEF 11EA A6FA (new)
    Good judgement comes with experience. Unfortunately, the experience
usually comes from bad judgement.